Date   
Re: Another scope 7854

Cliff Carrie
 

I had a 7A26 with intermittent vertical instability in channel 2 only. I found that alongside the attenuator plug-in modules, there are discrete 1/8 watt resistors. They are also plugged in and one had developed high contact resistance. I replugged it about 4 times after using a q-tip to swab its leads with contact cleaner, being careful not to get it anywhere except on the ends of the leads. The problem never came back.


Cliff Carrie

________________________________
From: TekScopes@... <TekScopes@...> on behalf of David @DWH [TekScopes] <TekScopes@...>
Sent: Thursday, May 4, 2017 7:22:26 AM
To: TekScopes@...
Subject: Re: [TekScopes] Another scope 7854



On Thu, 4 May 2017 02:10:45 -0500, you wrote:

So by attenuators modules you mean the little plastic boxes under the aluminum shielding? Each box has two trim caps?? I just pull those up and re-seat them? Any trick or special tool required other than patience and care?
Those are them. They are mounted just like big 4 pin ICs.

I already cleaned and aligned the cam switches. They seem to be working better, but I still have an overall gain issue on ch2 (about 5X too much gain on all volts/div settings). I turned down the gain setting using the push in with a screwdriver method on the variable gain on the front of the unit. That did not go low enough. I checked the resistors around the gain pots and they check out in spec. That push in gain pot was going down to about 1 Ohm.

Perhaps this is caused one of those modules.
5 times too much gain at all volt/div settings? No, that is some
other problem and an odd one. The frequency response should be
screwed up also.

A shorted C375 shown on schematic 4 would cause about that much high
gain. A shorted C445 shown on schematic 3 could cause it if R445 is
adjusted to a low value.

Comparing the DC levels at different points between channel 1 and
channel 2 should help find the problem.

Interesting indeed. That 2465 family is a great bang for the buck. I was mainly trying to justify buying (albeit cheaply, locally, and with a real nice Tek cart included) the 7854. The GPIB might be interesting to mess with, and there are other features to justify it.
The averaging capability is very nice in some applications. Except
for that, the 7854 is a slightly slower 7904 to most users.




[Non-text portions of this message have been removed]

Re: Type 503 Oscilloscope Issues

Evan
 

The warping phenomena that I have been observing is that the waves periodically stretch and compress horizontally around the center of the scope after a certain amount of time running. This may be normal behavior, but it only occurred more frequently before the scope had died. When using the scope in X-Y mode, it results in non-symmetrical Lissajous circles.

As for the measurements, I will double check them later tonight with another DMM that I can borrow from a lab that has smaller alligator clip leads (and try to fit them better around the resistors for measurements).


All of the measurements I made had the probes attached before the scope is on, and I turn it off between each test point to avoid any shorts.


Evan

Re: Type 503 Oscilloscope Issues

ykochcal
 

I don't know if an earlier 1:18AM email got posted that I sent, I don't see
it.

In any case I would focus on the 85V and regulator circuit, as it should be
fairly independent of the 3000V issues if any.

Focus on R640 one side should be connected to the 85V wires, you should be
able to follow it there.

The resistance readings on R640, R641 R642 and R644 look reasonable for in
circuit measurements starters

Your voltage readings do not jive in any way.

If your readings are correct you have

8-9V on the 85V line and then

+11V on one side of R640 and +91.2V on the other

Then one side of R640 goes to R641 where you measure

+0.8V on the right and +5.1V on the left


But the 85V supply line should be the same as one side of R640

And one side of R641 should be the same as the other side of R640

Are the voltage readings jumping around?



Again I would carefully follow all the connections of the 85V line from R659
and V659 connection to R640 so you know there is not another connection
somewhere. ( I assume from looking at the schematic that it does not but
that is based on not finding anything that is labeled +85V but that's not a
sure method)

The follow that to R641 and back to R642 so you know what side of the
resistor is what.

I don't have a unit to be able to tell which side of a resistor is what on
the schematic. It would be much more illuminating if you trace the
connections and place the voltages on the schematic at the point they are
taken.

So to sum up the voltages look in the ball park except R640's and the +85V
supply.

John

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Thursday, May 04, 2017 9:52 AM
To: TekScopes@...
Subject: [TekScopes] Re: Type 503 Oscilloscope Issues

So in response to the previous points:

1. I did mean V692, regarding it not lighting up. Normally, the -3000 V
tube comes on after a minute, once the scope warms up. However, with the
probe clipped to +85V bus, the tube never turns on. But looking now at V659,
that also does not turn on if the probe is attached (when normally is it a
bright orange glow).
Re-measuring R692, the resistor comes to 4.4 ohm, which is in its normal
range. I am not sure why the previous reading was so high.


2. The resistance across Pin 1 to Pin 5 of V659 measures at 4.5 ohm with
the tube removed. With the tube installed, the resistance from Pin 1/5 to
ground is 100.2 kOhm. No visible short is present. The voltage on both pins
is the same, and the value has not changed since last I reported it (between
8-9 V).


3. Voltages measured from both sides of the resistors:
R640 -> +11 V from the left, +91.2 V from the right
R641 -> +0.8 V from the right pin (and trace appears, tubes normal), +5.1 V
from the left pin (dim trace appears, V692 not fully glowing, faint orange)
R642 -> -87.3 V from the left, +1.7 V from the right
R644 -> The left side measured at -0.3 V, while the right side gave no
reading (0 V). This may be due to probe position, since I could not put the
probe in the tight space very well while avoiding touching any of the other
wires (had to place on the middle pin of R641, which is soldered to R644).


>> Note that R641 was a bit hard to turn initially when I tested it a week
ago, but now it is fairly easy to adjust.


I have updated the schematic with the new resistor readings and voltages,
and can be found with the previous link:
https://goo.gl/photos/4vv9VNR68bkhTUdG9
https://goo.gl/photos/4vv9VNR68bkhTUdG9. Note that R624 corresponds to the
resistor that is directly across Pins 6 and 8 of the socket for V620, but it
is not shown on the schematic. Pin 6 appears to just lead to the grounding
bracket.


Also of note, using the scope in X-Y mode, the -Input of the Horizontal
adjust is very skewed/out of proportion, while the +/-Input of the Vertical
adjust and the +Input of the Horizontal adjust appear to work as normal,
minus the general warping of the trace image (not sure if this issue is
specifically related to the issues on the other parts of the scope).




- Evan







------------------------------------
Posted by: enchanter464@...
------------------------------------


------------------------------------

Yahoo Groups Links

Re: 7S14 with not working CH2

Eino Väänänen
 

There is still something wrong. There is much noise or something in both traces and the amplitudes are about 25 % low. The noise is also there in the earlier picture but it is stronger now. Picture is here:


https://www.flickr.com/photos/149607134@N07/33641113913/in/dateposted-public/ https://www.flickr.com/photos/149607134@N07/33641113913/in/dateposted-public/


Do the samplers need adjustment? Voltages of the batteries look fine. I have soldered the batteries (type 13 ZincAir) to the sampler board. Maybe the solder prevents the battery to get oxygen?


Eino

Re: Type 503 Oscilloscope Issues

Dave Casey
 

It certainly sounds like your meter is loading the +85V bus and killing it,
but your story is not consistent. You measured the +85V bus again when you
took voltage readings at R640 and saw it read 91.2V. What's different
between how you performed these two measurements? Was the scope switched on
after you attached the probe at V659 but already up and running when you
measured R640? Perhaps the minor loading of your DMM is not enough to kill
the supply but is enough to keep it from starting.
What warping of the trace are you talking about? It looks pretty good in
the photos/video you've posted.

Dave Casey

On Thu, May 4, 2017 at 11:52 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



So in response to the previous points:

1. I did mean V692, regarding it not lighting up. Normally, the -3000 V
tube comes on after a minute, once the scope warms up. However, with the
probe clipped to +85V bus, the tube never turns on. But looking now at
V659, that also does not turn on if the probe is attached (when normally is
it a bright orange glow).
Re-measuring R692, the resistor comes to 4.4 ohm, which is in its normal
range. I am not sure why the previous reading was so high.


2. The resistance across Pin 1 to Pin 5 of V659 measures at 4.5 ohm with
the tube removed. With the tube installed, the resistance from Pin 1/5 to
ground is 100.2 kOhm. No visible short is present. The voltage on both pins
is the same, and the value has not changed since last I reported it
(between 8-9 V).


3. Voltages measured from both sides of the resistors:
R640 -> +11 V from the left, +91.2 V from the right
R641 -> +0.8 V from the right pin (and trace appears, tubes normal), +5.1
V from the left pin (dim trace appears, V692 not fully glowing, faint
orange)
R642 -> -87.3 V from the left, +1.7 V from the right
R644 -> The left side measured at -0.3 V, while the right side gave no
reading (0 V). This may be due to probe position, since I could not put the
probe in the tight space very well while avoiding touching any of the other
wires (had to place on the middle pin of R641, which is soldered to R644).


Note that R641 was a bit hard to turn initially when I tested it a week
ago, but now it is fairly easy to adjust.


I have updated the schematic with the new resistor readings and voltages,
and can be found with the previous link: https://goo.gl/photos/
4vv9VNR68bkhTUdG9 https://goo.gl/photos/4vv9VNR68bkhTUdG9. Note that R624
corresponds to the resistor that is directly across Pins 6 and 8 of the
socket for V620, but it is not shown on the schematic. Pin 6 appears to
just lead to the grounding bracket.


Also of note, using the scope in X-Y mode, the -Input of the Horizontal
adjust is very skewed/out of proportion, while the +/-Input of the Vertical
adjust and the +Input of the Horizontal adjust appear to work as normal,
minus the general warping of the trace image (not sure if this issue is
specifically related to the issues on the other parts of the scope).




- Evan


[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]

Re: Type 503 Oscilloscope Issues

Evan
 

So in response to the previous points:

1. I did mean V692, regarding it not lighting up. Normally, the -3000 V tube comes on after a minute, once the scope warms up. However, with the probe clipped to +85V bus, the tube never turns on. But looking now at V659, that also does not turn on if the probe is attached (when normally is it a bright orange glow).
Re-measuring R692, the resistor comes to 4.4 ohm, which is in its normal range. I am not sure why the previous reading was so high.


2. The resistance across Pin 1 to Pin 5 of V659 measures at 4.5 ohm with the tube removed. With the tube installed, the resistance from Pin 1/5 to ground is 100.2 kOhm. No visible short is present. The voltage on both pins is the same, and the value has not changed since last I reported it (between 8-9 V).


3. Voltages measured from both sides of the resistors:
R640 -> +11 V from the left, +91.2 V from the right
R641 -> +0.8 V from the right pin (and trace appears, tubes normal), +5.1 V from the left pin (dim trace appears, V692 not fully glowing, faint orange)
R642 -> -87.3 V from the left, +1.7 V from the right
R644 -> The left side measured at -0.3 V, while the right side gave no reading (0 V). This may be due to probe position, since I could not put the probe in the tight space very well while avoiding touching any of the other wires (had to place on the middle pin of R641, which is soldered to R644).


>> Note that R641 was a bit hard to turn initially when I tested it a week ago, but now it is fairly easy to adjust.


I have updated the schematic with the new resistor readings and voltages, and can be found with the previous link: https://goo.gl/photos/4vv9VNR68bkhTUdG9 https://goo.gl/photos/4vv9VNR68bkhTUdG9. Note that R624 corresponds to the resistor that is directly across Pins 6 and 8 of the socket for V620, but it is not shown on the schematic. Pin 6 appears to just lead to the grounding bracket.


Also of note, using the scope in X-Y mode, the -Input of the Horizontal adjust is very skewed/out of proportion, while the +/-Input of the Vertical adjust and the +Input of the Horizontal adjust appear to work as normal, minus the general warping of the trace image (not sure if this issue is specifically related to the issues on the other parts of the scope).




- Evan

Re: 7S14 with not working CH2

 

Talking of 7S14 - anyone in the UK have a spare one of these - always rather
fancied having one, and never found one so far.

Dave

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 04 May 2017 14:47
To: TekScopes@...
Subject: RE: [TekScopes] Re: 7S14 with not working CH2

> Are there any sustitutes?


Eino
See my earlier mail :-)

It is a bit fiddly because the SM package is very much smaller than the Tek
original, but with care it is entirely possible. This (once I have done it
with the 7S14) will be the third sampler I've resurrected in this way.

Craig





Thanks Craig and all who have helped me!


I have now changed the diodes to substitutes which Craig proposed. 7S14
plugin works now fine on both channels! Look at the pcture from this link:



https://www.flickr.com/photos/149607134@N07/34406119396/in/dateposted-public
/
https://www.flickr.com/photos/149607134@N07/34406119396/in/dateposted-public
/


Eino











------------------------------------
Posted by: einovaan@...
------------------------------------


------------------------------------

Yahoo Groups Links

Re: 7S14 with not working CH2

Eino Väänänen
 

Are there any sustitutes?


Eino
See my earlier mail :-)

It is a bit fiddly because the SM package is very much smaller than the Tek original, but with care
it is entirely possible. This (once I have done it with the 7S14) will be the third sampler I've
resurrected in this way.

Craig





Thanks Craig and all who have helped me!


I have now changed the diodes to substitutes which Craig proposed. 7S14 plugin works now fine on both channels! Look at the pcture from this link:


https://www.flickr.com/photos/149607134@N07/34406119396/in/dateposted-public/ https://www.flickr.com/photos/149607134@N07/34406119396/in/dateposted-public/


Eino

Re: AF501 woes

 

On 04 May 2017 01:41:48 +0000, you wrote:

Thanks Dave.

I added two more photos.

- The one with two traces shows the trigger pulse (top) and the input signal (bottom).
- The one with three traces shows trigger (top), signal (middle), and output at pin 7 of the comparator (bottom).

The glitch is towards but slightly before the bottom of the cycle, so there is a phase advance happening as well as the frequency doubling.

The comparator output doesn't change, apart from size and frequency, when I vary the amplitude or frequency into/out of the problem zones that exhibit the trigger glitch.
So the glitch is produced on the falling edge of the comparator
output. I expected that but wanted to make sure.

However I finally measured the comparator supply voltages and they are +15V and -9V, which should be +15/-3V, so the zener VR272 is faulty, which I will fix ASAP, and I guess we now have to wonder whether that is a possible cause.
Oh, bingo. If the comparator's output voltage changes by too much on
the high to low transition, then the base-emitter junction of Q298
which only has a rating of like 5 volts will be reverse biased into
breakdown causing Q298 to behave strangely. In this case, it
momentarily turns on by charge pumped through C296.

U290 is only rated for +14 and -7 volt supply voltages maximum but I
do not think it has been damaged because R272 is limiting the negative
supply current.

So -9 volts applied to the comparator negative supply pin instead of
-3 volts completely explains what is happening.

Re: Tek 549 - HV transformer

Kevin Wood G7BCS
 

If my memory serves, and it's the same as my 546, there's a resistor in
series with the HT supply to the HV oscillator. You can watch the voltage
across this with a multimeter to monitor the current drawn by the HT
circuit. You will see this climbing as the transformer heats up, as
confirmation that the losses in the circuit are increasing.

The other thing you can do without getting involved in measuring kilovolts
is to look at the DC conditions around the smaller tube that regulates the
HV output.

The normal failure mode is for the trace to start to "bloom" when you
adjust the intensity as the HV loses regulation and it used to take a good
30 minutes running for mine to reach this state. It never got bad enough
to lose the trace completely. It sounds like yours is a more sudden
failure than this, but it is worth investigating the transformer when any
HV related failures occur.

Cheers,

Kevin
G7BCS

Good to know and thanks. Just a matter of checking the HV while it's in
fail mode, I think.




Garrett

S2A timebase for DM83 scope

James R. Bartlett
 

Hello to the group.
A regular reader and learner but not a frequent poster.
I wonder by any miricle would there be anyone in the group that would have
a S2A timebase for an old Telequipment D83 scope. I am in need of one also
looking for the Perspex ? knob as used on the Delayed timebase.
.
If not available does anyone know where I might purchase same.
Many thanks
Jim
Ei2BB

Re: Equivalent time-and-bit-depth sampling?

 

Aliasing if it exists in a dithered signal does not matter.
Characteristics like peak, average, and standard deviation are not
changed by aliasing.

Sweeping the signal level like that is a way to make a ramp type of
analog to digital converter.

On Thu, 04 May 2017 04:29:57 +0000, you wrote:

Hi David,
In dithering the signal still only makes the signal traverse roughly one
least significant bit of headroom - in my case it would traverse the whole
headroom between the captured voltage (+overshoot) and zero. That is the
property I thought would bring an advantage. In addition it does so
"slowly", i.e. nearly all of this traversal happens at very low slew rates
compared to the slew rate of the high frequency components of Gaussian
noise, which in turn means you are not limited by the performance of the
ADC near Nyquist, and don't need to worry about aliasing as much. I believe
this could be another advantage.

Re: Another scope 7854

 

On Thu, 4 May 2017 02:10:45 -0500, you wrote:

So by attenuators modules you mean the little plastic boxes under the aluminum shielding? Each box has two trim caps?? I just pull those up and re-seat them? Any trick or special tool required other than patience and care?
Those are them. They are mounted just like big 4 pin ICs.

I already cleaned and aligned the cam switches. They seem to be working better, but I still have an overall gain issue on ch2 (about 5X too much gain on all volts/div settings). I turned down the gain setting using the push in with a screwdriver method on the variable gain on the front of the unit. That did not go low enough. I checked the resistors around the gain pots and they check out in spec. That push in gain pot was going down to about 1 Ohm.

Perhaps this is caused one of those modules.
5 times too much gain at all volt/div settings? No, that is some
other problem and an odd one. The frequency response should be
screwed up also.

A shorted C375 shown on schematic 4 would cause about that much high
gain. A shorted C445 shown on schematic 3 could cause it if R445 is
adjusted to a low value.

Comparing the DC levels at different points between channel 1 and
channel 2 should help find the problem.

Interesting indeed. That 2465 family is a great bang for the buck. I was mainly trying to justify buying (albeit cheaply, locally, and with a real nice Tek cart included) the 7854. The GPIB might be interesting to mess with, and there are other features to justify it.
The averaging capability is very nice in some applications. Except
for that, the 7854 is a slightly slower 7904 to most users.

Re: Type 503 Oscilloscope Issues

ykochcal
 

Another thought. The regulator tubes like V659 often have two pins connected
inside (like 1 and 5 in this case) and the tube is actually wired so the
supply is connected with a resistor to one pin R659 that gets the gas
discharging at the needed voltage and then the other pin is where the
regulated voltage is taken from.

That way if the tube is pulled the "regulated" voltage drops down rather
then being pulled up towards the higher voltage supply value, with the tube
pulled the supply is designed to lower it's voltages.

Look closely as to how V659 pin 1 and 5 is connected to R659 and the +250V
and R640 of the regulator.

It's possible you have a socket connection issue on the output pin and
pulling it in and out a few times might clear it

Measure voltage on both pins 1 and 5 to be sure they are the same

I have forgot if you can see a discharge glow in V659 or not

John

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Wednesday, May 03, 2017 10:24 PM
To: TekScopes@...
Subject: [TekScopes] Re: Type 503 Oscilloscope Issues

Hello all,


So I just realized that I had two of the wires flipped from the diagram
that Dave had sent. I wired in sequential order, and did not realize that my
wiring to Pins 2 and 3 should be flipped. With that corrected, the trace
does appear, and the scope seems to be running normally (or at least as it
was before). However, running some sine waves through the scope, there
appears to be some distortion of the curves, with a warping of the image
towards the center of the display. This was present the last time the trace
had worked as well. The scope also seems to be running hot (although it may
have always done that).


I have pictures of the resistor readings and the wiring of the new 6.3 VAC
transformer here: https://goo.gl/photos/4vv9VNR68bkhTUdG9
https://goo.gl/photos/4vv9VNR68bkhTUdG9. Please disregard the tape wrapping
of the secondary wire going to the original Pin 6 wire. I only made it white
and orange to remind me that the wire is being elevated to -3000 V (same
color as the scope's HV wires).


From John, I had overlaid the schematic you sent with the resistor readings
from before. I do have the earlier model of the scope, as from previously
noting that I only have two tubes on the 12.6 V circuit (V334 and V434, both
6DJ8's). My serial number is 004418 if that helps (never did post it
before). From the Tektronix Service Scope issues I have from 1962, I know
that this model does not have some of the fixes that those >7000 had gotten
from the factory, but they were nothing that should prevent it from powering
correctly.

As for R659, it gave the same reading as before, at ~77.6 kOhm. The only
resistor that seems to have taken a beating from the arc was R626 (slight
black scorch mark on the top), but it still reads at 40.1 kOhm.


Since the transformer is now wired in correctly, and the resistors do not
seem to be damaged from yesterday's event, I re-did the voltage measurements
(being sure not to short anything this time).


I tried to adjust the -100 V bus via R641, but the largest value I could
get the voltage to was still just -85 V. The voltage using the original R641
setting gave -80 V when the transformer was correctly wired, so it does
influence the voltage.


With the -100 V bus adjusted, I measured the other buses (although I know
they will be skewed because the -100 V is still not correct).
+250V measured at 305 V
+100V measured at 110 V
+12.6V measured at ~18 V
+500V measured at 470 V
+85 gave the same issue as before (~8.5 V, and no V692 turning on).


As Dave inquired, I am not actually using the analog voltmeter for these
readings. I am currently using my only "good" DMM (the one I used to
calibrate the analog meter), due to misplacing one of the analog meter's
probes. Since it uses non-jacketed banana leads, I am not able to use the
probes from any of my other meters, so I just have to base everything on the
DMM for right now.


- Evan











------------------------------------
Posted by: enchanter464@...
------------------------------------


------------------------------------

Yahoo Groups Links

Re: Type 503 Oscilloscope Issues

ykochcal
 

Well it looks like good progress.

Looking at the schematic with resistor readings things generally look good.
I assume you mean R621 is 94.6 K ohm (missing the K on your sheet)
And I did not know what R624 was pointing to or referenced.

But given that The readings all seem to me to be about what one would expect
with resistors that have parallel resistor networks as shown.

R692 being the exception that looks too high, did you short your probes and
take a reading before so you can subtract the lead resistance? In any case I
It may work with that value, and you have other issues that are not HV
related.

As for the voltages I would say that the regulation is based on the -100V,
but in this system all the voltages are tied to the transformer winding
ratio (except the -85 which is at the gas tube discharge value)

All your voltages are high (in absolute value) except the -100V

So it would seem that you oscillator is running full throttle trying to get
the -100V where it should be and in that process is pushing all the other
supplies too high.

What is V659's resistance from pin 1,5 to ground? I would think it should be
in the 50K range, possible the tube is shorted?

If the 85V is low, you need to check to be sure it only goes to R640.
And look closely that it's not got a visual short to something.

And then take some voltage readings at all nodes at the each ends of R640,
R641, R642 and R644 mark up a schematic and report

That might help pinpoint the issue.

You have turned R641 how does it feel?

John

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Wednesday, May 03, 2017 10:24 PM
To: TekScopes@...
Subject: [TekScopes] Re: Type 503 Oscilloscope Issues

Hello all,


So I just realized that I had two of the wires flipped from the diagram
that Dave had sent. I wired in sequential order, and did not realize that my
wiring to Pins 2 and 3 should be flipped. With that corrected, the trace
does appear, and the scope seems to be running normally (or at least as it
was before). However, running some sine waves through the scope, there
appears to be some distortion of the curves, with a warping of the image
towards the center of the display. This was present the last time the trace
had worked as well. The scope also seems to be running hot (although it may
have always done that).


I have pictures of the resistor readings and the wiring of the new 6.3 VAC
transformer here: https://goo.gl/photos/4vv9VNR68bkhTUdG9
https://goo.gl/photos/4vv9VNR68bkhTUdG9. Please disregard the tape wrapping
of the secondary wire going to the original Pin 6 wire. I only made it white
and orange to remind me that the wire is being elevated to -3000 V (same
color as the scope's HV wires).


From John, I had overlaid the schematic you sent with the resistor readings
from before. I do have the earlier model of the scope, as from previously
noting that I only have two tubes on the 12.6 V circuit (V334 and V434, both
6DJ8's). My serial number is 004418 if that helps (never did post it
before). From the Tektronix Service Scope issues I have from 1962, I know
that this model does not have some of the fixes that those >7000 had gotten
from the factory, but they were nothing that should prevent it from powering
correctly.

As for R659, it gave the same reading as before, at ~77.6 kOhm. The only
resistor that seems to have taken a beating from the arc was R626 (slight
black scorch mark on the top), but it still reads at 40.1 kOhm.


Since the transformer is now wired in correctly, and the resistors do not
seem to be damaged from yesterday's event, I re-did the voltage measurements
(being sure not to short anything this time).


I tried to adjust the -100 V bus via R641, but the largest value I could
get the voltage to was still just -85 V. The voltage using the original R641
setting gave -80 V when the transformer was correctly wired, so it does
influence the voltage.


With the -100 V bus adjusted, I measured the other buses (although I know
they will be skewed because the -100 V is still not correct).
+250V measured at 305 V
+100V measured at 110 V
+12.6V measured at ~18 V
+500V measured at 470 V
+85 gave the same issue as before (~8.5 V, and no V692 turning on).


As Dave inquired, I am not actually using the analog voltmeter for these
readings. I am currently using my only "good" DMM (the one I used to
calibrate the analog meter), due to misplacing one of the analog meter's
probes. Since it uses non-jacketed banana leads, I am not able to use the
probes from any of my other meters, so I just have to base everything on the
DMM for right now.


- Evan











------------------------------------
Posted by: enchanter464@...
------------------------------------


------------------------------------

Yahoo Groups Links

Re: Another scope 7854

Joe Laffey
 

On May 3, 2017, at 10:43 PM, David @DWH [TekScopes] <TekScopes@...> wrote:

On Wed, 3 May 2017 19:50:55 -0500 (CDT), you wrote:

The 7A18 has some issues. Channel 1 seems fine, but Channel 2 has a lot of
noise on it (need to check the exact value, but the line is about 4 times
thicker than Channel 1). It also seem to have all of its attenuator values
off by around one click of the switch (not exactly). All waveforms
have much greater vertical amplitude then they should. The readout display
is correct based on the switch position.
Sounds like some of the cam switches are not making complete contact
but also check the attenuator modules. They are socketted and
sometimes need to be reseated. In some cases, the connections between
the exposed pins and the hybrid inside can go open; if this is the
case, they can be resoldered with silver solder after removing the
plastic top from the module which just pops off.
So by attenuators modules you mean the little plastic boxes under the aluminum shielding? Each box has two trim caps?? I just pull those up and re-seat them? Any trick or special tool required other than patience and care?

I already cleaned and aligned the cam switches. They seem to be working better, but I still have an overall gain issue on ch2 (about 5X too much gain on all volts/div settings). I turned down the gain setting using the push in with a screwdriver method on the variable gain on the front of the unit. That did not go low enough. I checked the resistors around the gain pots and they check out in spec. That push in gain pot was going down to about 1 Ohm.

Perhaps this is caused one of those modules.

I will reseat the ICs. I don't think I see any socketed transistors.

It is not quite that simple. The 200MHz 7A26 is only 180MHz in the
7854 and almost all of the faster high input impedance vertical
amplifiers are 50 ohms only. So in a practical sense, your 2465 is
usually 300MHz while the 7854 is limited to 180MHz when used with
common x10 high impedance passive probes.

On the other hand, high impedance passive probes are anything but high
impedance at high frequencies where low-z probes or FET probes should
be used. But the dual trace 7A24 is only 300MHz in the 7854 which is
no faster than your 2465.

Interesting indeed. That 2465 family is a great bang for the buck. I was mainly trying to justify buying (albeit cheaply, locally, and with a real nice Tek cart included) the 7854. The GPIB might be interesting to mess with, and there are other features to justify it.

Thanks for the compatibility info as well. This is all great data.

--
73
Joe Laffey

Re: Type 503 Oscilloscope Issues

Dave Casey
 

Evan -

Glad we've managed to at least get you back to where you started before the
scope died. To clarify, when you measure the +85V bus, you see the low
voltage of about 8,5V and V659 (you said V692, but I think you mean V659)
is dark. When you are not measuring this bus, is V659 still dark?

Dave Casey

On Thu, May 4, 2017 at 12:23 AM, enchanter464@... [TekScopes] <
TekScopes@...> wrote:



Hello all,


So I just realized that I had two of the wires flipped from the diagram
that Dave had sent. I wired in sequential order, and did not realize that
my wiring to Pins 2 and 3 should be flipped. With that corrected, the trace
does appear, and the scope seems to be running normally (or at least as it
was before). However, running some sine waves through the scope, there
appears to be some distortion of the curves, with a warping of the image
towards the center of the display. This was present the last time the trace
had worked as well. The scope also seems to be running hot (although it may
have always done that).


I have pictures of the resistor readings and the wiring of the new 6.3 VAC
transformer here: https://goo.gl/photos/4vv9VNR68bkhTUdG9
https://goo.gl/photos/4vv9VNR68bkhTUdG9. Please disregard the tape
wrapping of the secondary wire going to the original Pin 6 wire. I only
made it white and orange to remind me that the wire is being elevated to
-3000 V (same color as the scope's HV wires).


From John, I had overlaid the schematic you sent with the resistor
readings from before. I do have the earlier model of the scope, as from
previously noting that I only have two tubes on the 12.6 V circuit (V334
and V434, both 6DJ8's). My serial number is 004418 if that helps (never did
post it before). From the Tektronix Service Scope issues I have from 1962,
I know that this model does not have some of the fixes that those >7000 had
gotten from the factory, but they were nothing that should prevent it from
powering correctly.

As for R659, it gave the same reading as before, at ~77.6 kOhm. The only
resistor that seems to have taken a beating from the arc was R626 (slight
black scorch mark on the top), but it still reads at 40.1 kOhm.


Since the transformer is now wired in correctly, and the resistors do not
seem to be damaged from yesterday's event, I re-did the voltage
measurements (being sure not to short anything this time).


I tried to adjust the -100 V bus via R641, but the largest value I could
get the voltage to was still just -85 V. The voltage using the original
R641 setting gave -80 V when the transformer was correctly wired, so it
does influence the voltage.


With the -100 V bus adjusted, I measured the other buses (although I know
they will be skewed because the -100 V is still not correct).
+250V measured at 305 V
+100V measured at 110 V
+12.6V measured at ~18 V
+500V measured at 470 V
+85 gave the same issue as before (~8.5 V, and no V692 turning on).


As Dave inquired, I am not actually using the analog voltmeter for these
readings. I am currently using my only "good" DMM (the one I used to
calibrate the analog meter), due to misplacing one of the analog meter's
probes. Since it uses non-jacketed banana leads, I am not able to use the
probes from any of my other meters, so I just have to base everything on
the DMM for right now.


- Evan










[Non-text portions of this message have been removed]

Re: Type 503 Oscilloscope Issues

Evan
 

Hello all,


So I just realized that I had two of the wires flipped from the diagram that Dave had sent. I wired in sequential order, and did not realize that my wiring to Pins 2 and 3 should be flipped. With that corrected, the trace does appear, and the scope seems to be running normally (or at least as it was before). However, running some sine waves through the scope, there appears to be some distortion of the curves, with a warping of the image towards the center of the display. This was present the last time the trace had worked as well. The scope also seems to be running hot (although it may have always done that).


I have pictures of the resistor readings and the wiring of the new 6.3 VAC transformer here: https://goo.gl/photos/4vv9VNR68bkhTUdG9 https://goo.gl/photos/4vv9VNR68bkhTUdG9. Please disregard the tape wrapping of the secondary wire going to the original Pin 6 wire. I only made it white and orange to remind me that the wire is being elevated to -3000 V (same color as the scope's HV wires).


From John, I had overlaid the schematic you sent with the resistor readings from before. I do have the earlier model of the scope, as from previously noting that I only have two tubes on the 12.6 V circuit (V334 and V434, both 6DJ8's). My serial number is 004418 if that helps (never did post it before). From the Tektronix Service Scope issues I have from 1962, I know that this model does not have some of the fixes that those >7000 had gotten from the factory, but they were nothing that should prevent it from powering correctly.

As for R659, it gave the same reading as before, at ~77.6 kOhm. The only resistor that seems to have taken a beating from the arc was R626 (slight black scorch mark on the top), but it still reads at 40.1 kOhm.


Since the transformer is now wired in correctly, and the resistors do not seem to be damaged from yesterday's event, I re-did the voltage measurements (being sure not to short anything this time).


I tried to adjust the -100 V bus via R641, but the largest value I could get the voltage to was still just -85 V. The voltage using the original R641 setting gave -80 V when the transformer was correctly wired, so it does influence the voltage.


With the -100 V bus adjusted, I measured the other buses (although I know they will be skewed because the -100 V is still not correct).
+250V measured at 305 V
+100V measured at 110 V
+12.6V measured at ~18 V
+500V measured at 470 V
+85 gave the same issue as before (~8.5 V, and no V692 turning on).


As Dave inquired, I am not actually using the analog voltmeter for these readings. I am currently using my only "good" DMM (the one I used to calibrate the analog meter), due to misplacing one of the analog meter's probes. Since it uses non-jacketed banana leads, I am not able to use the probes from any of my other meters, so I just have to base everything on the DMM for right now.


- Evan

Re: Equivalent time-and-bit-depth sampling?

 

Hi David,
In dithering the signal still only makes the signal traverse roughly one
least significant bit of headroom - in my case it would traverse the whole
headroom between the captured voltage (+overshoot) and zero. That is the
property I thought would bring an advantage. In addition it does so
"slowly", i.e. nearly all of this traversal happens at very low slew rates
compared to the slew rate of the high frequency components of Gaussian
noise, which in turn means you are not limited by the performance of the
ADC near Nyquist, and don't need to worry about aliasing as much. I believe
this could be another advantage.

On Wed, 3 May 2017 18:56 David @DWH [TekScopes], <
TekScopes@...> wrote:

On Wed, 03 May 2017 15:07:43 +0000, you wrote:

I assumed that the device holding the charge would be non-linear? On the
other hand the filter can be linear.
Sample and holds can be pretty linear or at least linear enough that
they do not hold back the ADC.

It is my hunch the resolution of sampling just one constant voltage is
going to be less than the resolution obtained by sampling a dynamic,
changing, signal, which depends on the charge.
This is what I meant by there is no need for this sort of complexity.

Almost all ADCs and especially fast ADCs have enough inherent noise
that nothing needs to be done at the input to dither the signal
allowing productive oversampling. If the ADC is quiet enough, and
some are like the ones used in the Tektronix 2232, then adding a
little bit of gaussian noise is easy enough; for instance noise could
be added to the reference input.


------------------------------------
Posted by: David <@DWH>
------------------------------------


------------------------------------

Yahoo Groups Links



Re: Suggestions for rehabbing a 466 w/ DM43

Fabio Trevisan
 

David,
Yep, essentially that is the idea but the solder doesn't actually need to
touch the board (although it doesn't hurt either).
Since molten solder has a high surface tension, you fill the crucible with
enough solder so that the molten solder surface is above the crucible edges
so, when you get the board closer and closer, the solder touches first the
tip of the components and it's surrounding solder... In that moment, the
solder around the leads immeditaly melts and is "pulled" by the Crucible's
solder (by capilarity or surface tension, I'm not sure exactly what's the
name of mechanism by which it happens).
You don't actually need to take the board closer than that because at this
point, the solder around all pins is already molten and the component is
free to be pulled from the other side.
In practice you apply some pulling force to the component before and as you
get the board closer and closer to the crucible.
At some point the component gets free and comes out and you can lift the
board away from the crucible.
If you apply some flux to the board before is even better as it helps the
molten solder to "wet" the pins/pads.
When you lift the board, it leaves the pads with an even and thin solder
coating.
Large holes are drained out and smaller holes remain filled with solder as
the hole's capillarity "hold" the solder inside them.
As with everything else, some practice is required and you can train
yourself on scrapped PCBs of any unrepairable device or equipment, such as
of computers, laptops and modern scopes :-).
Kidding... One cheap stuff that is often discarded such as desktop PC power
supply boards usually have the kind of bigger components (like big
transistors hooked together with their solderable heat sinks) that allow
you to get the "touch" quickly.

Brgrds,

Fabio

On May 3, 2017 10:01 PM, "David Berlind david@... [TekScopes]" <
TekScopes@...> wrote:



So, the PCB essentially had to make contact with the melted solder in the
crucible?

On May 3, 2017 8:07:40 PM "Fabio Trevisan fabio.tr3visan@...
[TekScopes]" <TekScopes@...> wrote:

Hi David,
I didn't but I wish I did because now I'm having to work around quite a
few
lifted pads and stripped-off metalized vias.
I do have, however, experience of a former job at a computer manufacturer
in Brazil where we had small crucibles, of about 3 cms diameter, to
unsolder hard stuff just like this... Multi pin connectors where the pads
were big (and retains a lot of solder and drains a lot of heat) all that
were a pain to remove by any other means, and were so easy to remove using
the crucible.
It was just a matter of carefully turning the PCB solder side down over
the
crucible so that it would melt all the pins simultaneously, wait for no
more than 2 seconds and pull the connector away.
They would come out so quickly that we could hold the connectors bare
handedly.
Of course that it has its down side...
It takes you to remove the board (which is not easy on the 4xx series
scopes), and sometimes takes additional measures such as removing
components around the area where the crucible will have to get close to
the
PCB, either not to damage the components or to clear the area so that you
can actually put the board in contact with the molten solder.
Back then, at a factory, we did that simply because it was faster and
cleaner, and usually there wasn't the down-side of having to disassemble
the equipment, because it was already disassembled.
At a repair shop, dealing with equipment that's still current, I think it
wouldn't be practical for the day to day use, due to the down-sides and
due
to the availability of parts to replace, should they get damaged in the
removal process..
Back to the restoration business (where we are) when a PCB that is, at
least, hard to get, and when you also don't want to destroy the old caps,
because you want to use their packaging as mechanical support for the new
ones, as I had to, I think that the additional preparation work is worth
it.
I wish I had a small crucible at hand when I started removing the caps.
But I fooled myself I would do it easily and I must confess I regret for
having insisted on doing it the hard way.
Later I went on looking for crucibles and found small ones for as cheap as
Brazilian 110,00 which is roughly 30,00 dollars.
I will look after one to have it around for the next occasions.

Brgrds,

Fabio


On May 3, 2017 7:06 PM, "David Berlind david@... [TekScopes]" <
TekScopes@...> wrote:



Hi Fabio,

I suspect that I will one day end up having to recap my 466... I was
curious about this statement:

*"get yourself asmall soldering crucible... because it takes too long to
unsolder thecapacitors using regular solder wick and solder vacuum-pump
and
the PCBsuffers. It's almost impossible not to end-up lifting some pads
and/ortracks or ripping-off some of the metalized thru holes (vias)."*

Can you explain how specifically you ended up using the crucible?

Thanks.

On Wed, May 3, 2017 at 5:43 PM, Fabio Trevisan fabio.tr3visan@...
[TekScopes] <TekScopes@...> wrote:



Hello Ryan,

I have a 464 (they're quite similar to the 466, exception to the H.V.
section that is simpler than that of the 466s) which I have went
through
all sort of minor problems since I bought it about 9 months ago.
Last "event" was that if finally blew one of its large P.S.
electrolytic
capacitors, the 1200uF x 120V.
On this last event (quite recent), I posted a question on this forum,
for
which I had quite some good advice from the folks.

Search for the thread:
Tek 464 - Big Caps recommnedation - Pot grease recommnedation

The original caps "form factor" is not in use presently and most you
will
find on the market are plain "Radial" caps, (with plain leads) or
"Snap-In"
caps that are usually short and fat (and some of them won't fit on the
1"
available space).
Neither fits-in mechanically / physically as the originals and both
require
some adaptation.
In recapping yours, you will have to make up your mind on either
following
the path of that guy you mentioned who recapped his 465 with Snap-In
capacitors (and connected them with wires and held them with plastic
brackets)... Or...
Buy pairs of smaller valued capacitors and mount them "In" the cans of
the
original caps (after opening them up and disposing their original
innards).

I followed the latter path and I`m just about to finish doing it...As
soon
as I can I will post to the pictures area of Tekscopes.
My solution was as follows:
500uF x 50V was replaced by 820 x 100V (it fits inside the can).
250uF x 150V was replaced by 330uF x 250V (if fits inside the can)
3 x 5500uF x 30V were replaced by 3 pairs of 3300uF x 63V (and each
pair
fits well inside the can)
1200uF x 100V were replaced by a rather long pair of 680uF x 160V (I
wish I
could have found shorter ones) They were 2 inches tall (each) and the
association didn't fit inside the can and I had to open the top of the
can
to mount them inside.

You will notice the C and V values are larger in all of them than the
originals, and this is not by chance. It's rather an advice from the
folks
of this forum to make up for the overall smaller ripple current ratings
of
the modern electrolytics.
Another advice is to try to have them all of 105C grade (the original
ones
were all 85C).

Last but not the least, on desoldering the old ones, if you plan to
follow
the 2nd path (and re-use the old capacitors base and cans), get
yourself
a
small soldering crucible... because it takes too long to unsolder the
capacitors using regular solder wick and solder vacuum-pump and the PCB
suffers. It's almost impossible not to end-up lifting some pads and/or
tracks or ripping-off some of the metalized thru holes (vias).

If you don't plan to use the older capacitor bases and cans, its better
to
just cut the old ones with a dremel cutting disc and pulling the
terminals
one by one.

Rgrds,

Fabio

2017-05-03 17:17 GMT-03:00 Ryan Stasel rstasel@... [TekScopes]
<
TekScopes@...>:




Hi All,

I picked up a Tek 466 w/ DM43 locally for $30 this week, and after
replacing the main fuse, it powered up, and after fiddling with
things
for
a while, it’s mostly “working”. Checking all the voltages, things
seem
good
and within tolerance. But it’s obvious all the caps are original to
the
unit… which, I have no good date on since I can’t find a serial
anywhere
(there is a hand written label on the tube shielding that says
92615).

Anyway, it’s pretty clear all the switches and pots need cleaning (do
most
suggest just using Deoxit spray, and maybe Fader Lube for the pots?),
and
the main caps need replacing. I’m also seeing a couple axial
electrolytic
caps on the “main” board (looking at the screen, the board along the
right
hand side) need replacing (they’re showing corrosion on the leads).
But
I’m
also curious if I should pull any of the socketed transistors or ICs
and
spray the sockets with cleaner and reseat, etc. The unit still acts a
bit
weird from time to time (screen blooms like it’s doing some storage
mode,
not showing both traces, not properly grounding the inputs when gnd
is
selected, etc).

I’m happy to link to pictures, etc… everything looks good, but
obviously
hasn’t been touched much since the unit was built. I’m also really
interested in what caps I should use for recapping the Power supply.
They’re a very odd size (tall and skinny), and looking online, I see
someone recapped a 465, but the new caps didn’t really match in size
at
all
so jumpers were needed. I’m pretty sure these size caps aren’t really
made
anymore, so I’m all for suggestions.

If anyone’s interested, it looks like my unit was tested by a
Kreurauko
(or something like that)… and the DM43 has “Donna” written on the
board
in
“Sharpie”. =)

Thanks very much!

-Ryan Stasel

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