Date   
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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Re: Another scope 7854

 

That is normal. The processor has better things to do during
aquisition than maintain the storage display and readout.

On Wed, 3 May 2017 20:46:19 -0500, you wrote:

Here's a question for somebody with a 7854:

When I use one of the Average functions to acquire an average waveform the readout display characters are kind of pixelated with random noise (like you overlaid random "off" pixels on top of the characters) during the acquisition. Once all the waveforms have been acquired and averaged the readout appears normal.

From the manual it seems like this should not happen and I should see a count of waveforms acquired. I can almost see this, but it is really rough looking. Again, once the waveform is acquired it looks fine.

Thanks.

Re: Another scope 7854

 

On Wed, 3 May 2017 20:29:48 -0500, you wrote:

On 05/03/2017 08:24 PM, David DiGiacomo telists@... [TekScopes] wrote:
Why would you say that?
Forgot. I use mine in store mode where there IS a 100MHz sampling speed that limits one shot events.

Thanks for correcting. It's one of 3 that are above my bench all the time: R7844, 2230, 7854
The sample rate is more like 400kHz with the 7B87.

Re: Another scope 7854

 

On Wed, 3 May 2017 22:04:32 -0500, you wrote:

Thanks for the info. Just because I am new to these dual trace mainframes... would you be able to use two 7A19 amplifiers with one 7A29 time base?
I think you mean 7B92A timebase.

Could I use 7A19 and the 7A18 that came with it, along with a time base and get three channels, albeit limited by the bandwidth of the 7A18?
This would absolutely work. I commonly use a 7A13 single trace and
7A26 dual trace like this.

Re: Another scope 7854

 

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.

I tried cleaning all the basic switches and pots, but I have not
disassembled the cam based switches on the attenuator controls. I was
wondering what special tricks there were to dealing with those. I am
guessing one of the contacts is dirty/bad.
Clean the cam switches by drawing isopropyl alcohol soaked clay free
paper or card stock through the closed switch; I like to use business
cards or 3x5 card stock. Vellum paper would also work well. It is
important to avoid common paper which has clay because the clay will
abrade the gold plating on the switches.

It is possible that some of the switches are not making good contact.
Tweezers can be used to bend the switch element where it meets the
leaf spring so that harder contact is made.

Do not lubricate these switch contacts.

Check the attenuator modules (under the aluminum covers) before
messing with the cam switches.

The scope also seems to have trouble triggering cleanly off Channel 2. I
will occasionally see a glitch waveform. I do not see this on Channel 1.
Also the glitches go away if I toggle the Channel 2 polarity switch to
invert mode. They also go away if I use DC Offset (Option 06) mode on the
7A18.

I am guessing I should start with the cam switches, but do those trigger
glitch criteria ring any bells with anyone?
The socketted transistors and ICs inside the 7A18 should be reseated.
The trigger source switching is done electronically but maybe the
mechanical wafer switch is dirty and needs to be cleaned.

Note that all of the above applies to the 7A26 as well.

Also, what is the fastest setup I can get with this 7854? The 7A24 with
its 50 Ohm 400MHz inputs? And the 7B85 ? Just trying to figure out the
ideal plugins to look out for. I'd like this to be my fast scope, possibly
supplanting the 2465 (300MHz).
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.

The recommended timebases are the 7B85 and 7B87 and operate up to
1ns/div. The 7B92A dual timebase can operate at up to 500ps/div. In
theory the 7B15 could replace the 7B85 to get 500ps/div capability
while keeping the 7B87.

The 7B87 timebase allows low sample rate single shot pretrigger
capability. It replaces the 7B80 which would normally be used but the
7B80 works fine also.

What happens if you try to run the 1GHz plugins in the 7854? Are they just
limited to 400MHz or what?
The 1984 Tektronix catalog has a table showing the vertical bandwidth
for different combinations of vertical amplifier and mainframe. For
the 7854:

7A11 200MHz Low Capacitance FET Single Trace
7A13 95MHz 1M Differential Comparator
7A16A 200MHz 1M Single Trace 20MHz Bandwidth Limit
7A18A 75MHz 1M Dual Trace
7A22 1MHz 1M Differential Amplifier 10uV/div
7A26 180MHz 1M Dual Trace 20MHz Bandwidth Limit
7A42 275MHz 1M Quad Trace Double Wide Logic Triggering

7A24 300MHz 50 ohms Dual Trace
7A19 400MHz 50 ohms Single Trace
7A29 400MHz 50 ohms Single Trace

The best general purpose vertical amplifier is the 7A26 because of its
dual channels, high bandwidth, high impedance inputs, and 20 MHz
bandwidth limit. The 7A29 is preferred to the 7A19 because it has
better input protection and is a better design.

This thing is pretty amazing considering the date of manufacture. Of
course it was over $30k in today's dollars...
Add in the cost of the vertical amplifiers and timebases and it is
more like $40k in today's dollars.

Re: Another scope 7854

Joe Laffey
 

On May 3, 2017, at 8:44 PM, @Raymond [TekScopes]
To fully utilise the horizontal and vertical speeds that the 7854 is capable of, a 7A19 (or 7A29) amplifier and a 7B92(A) would be a very nice setup. Be aware that the 7A19 and 7A29 are single-channel and that the 7B92(A) is a dual time base with delay.
With a 7B92(A) you'd have one horizontal slot unused. A 7D15 counter/timer would be nice to have real-time frequency and timing info.
Thanks for the info. Just because I am new to these dual trace mainframes... would you be able to use two 7A19 amplifiers with one 7A29 time base?

Could I use 7A19 and the 7A18 that came with it, along with a time base and get three channels, albeit limited by the bandwidth of the 7A18?

Thanks.
--
Joe Laffey

Re: Tek Blue paint source?

 

They can indeed but my experience has been that it is difficult for them to do a good match
I brought the case of my 465 with blank spots on its bottom to where I got my paint. They mixed silk-gloss paint to perfection which I used for touching up. It is almost impossible to see where corrections were made, both in daylight and artificial light.
Admittedly, I was stunned but then, these people are known as *the* specialists.
They stored their recipe as "Tek blue" at my request...

Raymond

Re: Tek Blue paint source?

Gary Robert Bosworth
 

Krylon "Bahama Sea" is very close. It cannot be used as touch-up, but is
near perfect if sprayed on all over. It is called Colormaster gloss.
Sherwin-Williams orders it for me and does not charge for the service.
Each can is about $6.00.

On May 3, 2017 6:03 PM, "Chris Elmquist chrise@... [TekScopes]" <
TekScopes@...> wrote:



Wondering if there is still a source for Tek Blue spray paint?

I've tried to contact Stan Griffiths here,

http://www.reprise.com/ash/clients2/parts_shop/contact.html

but the email is bouncing. He used to be able to supply it in spray
cans, apparently having it mixed by the same Sherwin-Williams outfit in
OR that Tek did.

I may have missed a discussion that Stan is no longer with us or no
longer in that business.

Any other sources or perhaps knowledge of the mixing codes so we can
get our own mixed locally?

Thanks and 73,

Chris NØJCF
--
Chris Elmquist



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