Date   
Re: Help with 7A18 problem

Bill Carns
 

What ?? Now confused. Was there something wrong with your first reply?

Bill

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Phillip Potter
Sent: Sunday, March 03, 2019 3:46 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with 7A18 problem

Please disregard!!!

Sorry,

Phil

On 3/3/2019 1:38 PM, Phillip Potter wrote:
Hi Bill,

I have the same amplifiers and when I first got them, had the same or
at least similar issues.

I tore them down, one at a time, and soaked 24lb bond with IPA, to
clean those switches. Yes, they are a bear to get to! IIRC, I had to
disassemble them down a ways to get into them. There were shields on
the inner sides and on the outer sides, too. Once I had them broken
down, it was a simple thing to get the soaked paper into the switch
fingers and carefully pull it through, in the same way that a
turntable moves a record under the stylus... never backward!

I recommend doing this somewhere where you can leave it laying,
disassembled, so that you can see how you got it apart, making it
easier to reassemble it. I took pictures on my phone at each step of
the way. It was a "trick" of a deal getting it broken down to the
point where it could be cleaned, however. Pictures helped me to stay
on track and get it all back together! Tektronix did it's homework...
they were made to be repaired... gotta love 'em!

I hope I've inspired you and not the opposite. I did have to work up
my nerve to tear into them, but the result was two operable
amplifiers, I am glad that I took my time and worked carefully.

Phil

On 3/2/2019 2:26 PM, Bill Carns wrote:
I'll have to go put the unit back in the mainframe and investigate
but my memory says that most were bad.

I have investigated more and remove the upper capacitor cover and,
boy are those things hard to get at. Gonna be real hard to get
cleaning paper in there on all the switches. Some are not bad,
others really bad to get to. One set has an additional little cover
over them for some reason.

Working on this thing is not for sissies.


B

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Albert Otten
Sent: Saturday, March 02, 2019 3:53 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with 7A18 problem

On Sat, Mar 2, 2019 at 07:58 PM, Colin Herbert wrote:

---
On the subject of the input attenuators, they are the type which are
operated by cam-switches. They have springy gold-plated contacts
that get moved up-and-down by cams on the controls shaft. The
circuit board that they are on has gold-plating, too, and the board
itself is made of an easily-damaged material. You need to use thin
strips of paper moistened in IPA and trapped between the moving and
stationary contacts, they *gently* pulling the paper strip out. You
may have to do this a few times. Don't use any other solvents or
contact-cleaner as you will probably ruin the board. Of course it
may only be one or two of these contacts that is dirty, as has
already been suggested; there are only four attenuators there - they
get switched in-and-out to get the different VOLTS/DIV settings. In
the most sensitive VOLTS/DIV setting, they are all switched out, so
if your 5mV/div setting shows lousy bandwidth, then it is likely to
be caused by some other problem, not just the attenuators and their
switching . Of course, there might be a problem there, too, but it
won't be the only one.
Hi Colin,

You probably were too quick in your statement about the 5 mV/div
setting. In that setting all attenuators are bypassed by means of a
series of closed contacts, so any dirty contacts there destroy the
signal path.
I'm not sure about the 7A18 construction. My impression is that
including AC/DC there are 10 contact pairs above the drum and 10
below the drum. (Each contact pair forming one switch).

It would still be nice to hear from Bill which V/div settings are
good and which are bad.

Albert








Re: Uncooperative 7834

fiftythreebuick
 

Definitely good ideas, Harvey! I particularly like the idea of pulsing a current limited supply into the rail and checking around along that rail for the lowest amplitude pulse. That should get you close to the offending component! Have to remember that one....



"Harvey White wrote:

There's another way, that's to take a current limited supply and pulse
it on and off. For a supply of X amps, I'd limit it to x/10 amps.
Now, if you have an HP current probe, the one that's made for shorted
nodes, you can see where the bright lights go, and that shows you the
track where the short is.

You might be able to make a probe that does that.

With this same setup, you can also take a probe and with a high
sensitivity range on the scope, look for the lowest amplitude of
pulse. You'd like to measure across the component itself, if at all
possible.

This is a different implementation of the second mode.

Harvey"

Re: Uncooperative 7834

Majdi S. Abbas
 

On Fri, Mar 01, 2019 at 06:11:50PM -0000, David C. Partridge wrote:
Specifed Measured
+130V 6.6k 6.8k
+50V 1.8k 1.75k
+15V 70R 52R
+5V 9R 8.4R
-15V 100R 60R
The -15V worries me a bit -- I've seen a shorted tantalum
around 40 ohms on this rail.

The character generator board has 1 uF tantalums directly
across the -15V and -50V rails; try disconnecting it and see
what happens with your -15V measurement.

--msa

Re: 2247A PSU Troubleshooting

Nicholas Keller
 

I finally got a chance to take a look at this 2247a. At the test point you
mentioned (c2202, before the startup and pre-regulator, marked 14A on the
schematic), I’m only getting 77VDC, but got about the same 77V when I
tested for AC. I measured 120-122VAC up to the diode ring. Does this
suggest that C2202 is bad? Or something else?

Thanks!

Nick





On Thu, Oct 25, 2018 at 12:55 PM @Nielsentelecom <
@Nielsentelecom> wrote:

Nick,

I have a 2246A that I had to overhaul, which most likely has the
identical power supply for your 2247A. I would do a search for the 2246A
power supply also here. So I will refer to the component number in your
schematic if there is a difference. I wouldn't be concerned with the diodes
and caps mentioned in Alex's post until you verify the following.

I also blew up U2201 when I accidentally shorted my scope probe shield
against a heatsink while probing. That caused a no power on the main 44VDC
bus measured at C2203. even if that is good, I would get a spare
replacement. they are not expensive and still available as of a couple
years ago.

Get the service manual, refer to page 97, or 3-59, the power supply block
diagram, and verify the voltage indicated prior to the preregulator and
startup circuit at c2202. that is the main DC bus that feeds the Switching
power supply pre-regulator. If you are plugged into 120VAC, it should be at
about 160-170VDC. then switch meter to AC, and see if there is any ripple
there. That's 120 hz so any meter will work. If that is good then check the
previous paragraph for the 44VDC check.

I also was able to test my power supply out of the cabinet. It was risky,
but necessary. I used a 10KV AC rated linemans glove and placed the CRT
lead inside of it. I also have the resistor values that were close loads
for the power supply to operate at a typical load.

NielsenTelecom



Re: Uncooperative 7834

 

On Mon, Mar 4, 2019 at 12:04 AM, fiftythreebuick wrote:


There's another way, that's to take a current limited supply and pulse
it on and off. For a supply of X amps, I'd limit it to x/10 amps.
Now, if you have an HP current probe, the one that's made for shorted
nodes, you can see where the bright lights go, and that shows you the
track where the short is.
Decoupling caps and tants and conducting PN junctions and regular power supply current would (partially) short out your pulse, thereby hiding the current info you're looking for, *unless* you use a low level, very low frequency, low slew rate signal.
A few months ago, I successfully used a low-level sinewave (about 0.4 Vpp) signal of about 10 Hz across the power supply pins with an HP 547A current tracer on a spectrum analyzer board, containing rows and rows of digital logic, 0.1" apart with dozens of interspersed decoupling caps. To my own amazement, it took about five minutes to find a shorted cap!

Raymond

Re: Uncooperative 7834

 

On Mon, Mar 4, 2019 at 12:27 AM, Raymond Domp Frank wrote:


low slew rate
Correcting myself: That snippet was left over editing away the erroneous mentioning of using a square wave (pulse). Please ignore.

Apparently, you don't have a full short. Still, traces of lower impedance readily come up by probing. Don't forget that the HP 547A is direction sensitive, so rotating it around an axis perpendicular to the trace indicates the direction of the current (modulo180 degrees)!

Raymond

Re: 475 with no Display and no HV

SuddenLink
 

Thank you so much Reed for the highly detailed roadmap to follow at this point and forward. I am going to read through your post a few more times to get a clear picture before I proceed.

One thing that still troubles me is why did the waveform at TP1318 go back down to less than 2 volts p-p and thus the HV disappear when I touched the test probe of my DMM to the Base of Q1306? Now I can’t tickle the HV back to life by touching the 1K resistor with the +5v rail at the other end to the base of Q1318 like I was able to do before.

One last data point: When I did have the shortened trace on the CRT I took my Simpson 260 with it’s 10KV high voltage probe to measure the voltage at the HV test point. It looks like it’s about 100 volts high (-2550).

Once again thank you for your help.

Ripley

The words are mine but this iPad does what it will with them.

On Mar 3, 2019, at 4:55 PM, Reed Dickinson <reed714@...> wrote:

I just re-read your trouble note and I suspect you have identified the problem when you said the trace is only 2/3 of the normal width. This points immediately to a defective U1321 voltage tripler. Unsolder the lead from T1320, pin 12, tripler and power on, look for normal waveforms around Q1318. If your tripler is defective a replacement 3X can be had in an NTE539 or ECG539 (an NTE538 or ECG538 would work too).
By momentarily connecting the base of Q1318 to +5 through a 1K resistor you have bypassed all the regulation that you get from Q1306 through Q1316 and you have proved that the transformer and associated circuit are working. The shortened trace you saw was probably due to the unregulated HV giving a shorter trace or a defective voltage tripler U1321. I would still look for problems around C1304. When you power up the time constant of R1304 and C1304 is about 680ms. This means that you have under a second for the HV to stabilize since the base of Q1306 is being pulled toward +110V until it is nailed at +0.6 by the conduction of CR1304. After about 1 second the base of Q1306 should go to about +0.6V and oscillations should occur via Q1318.
To troubleshoot the regulator circuit pull F1318 out and disconnect P1313, the transistor Q1318 is now out of the circuit. Connect a 25K pot between +15 and - 5 and connect the wiper of the pot through a 10K resistor to the Q1306 base node. Connect a sensitive voltmeter to the - side of C1316 and power on your scope. Connect another voltmeter to the Q1306 base node and vary the pot. When the base of Q1306 is around +0,6V you should see some variation at the - side of C1316 (a 4.7K temporary resistor to ground will be necessary to give a little current through Q1316), If no variation is seen when rotating the pot then you have a problem in the regulator circuit, troubleshoot it and you will find the problem. If a variation is seen then the regulator is working and you need to fix problems on the secondaries of the transformer. Before using the following shotgun replacement procedure unsolder the lead from T1320 pin 12 going to the 3X voltage multiplier. If the multiplier is bad it would put a load on the oscillator circuit and kill the oscillations. Next, use the shotgun approach and replace C1320, CR1320, CR1321, C1322, C1323, C1328 and CR1329. I recommend you use HV caps rated at least 5KV as the surge of HV during the first second is high.
Good luck:
Reed Dickinson
On Sunday, March 3, 2019, 12:01:12 PM PST, SuddenLink <bob.ripley@...> wrote:

I missed identified C1304. Instead it was C1468 with a broken lead that I pulled from the circuit board. A perfect example of a mistake made when one works on a problem to long without stepping away for a while.

C1436 on the -8 volt rail was replaced with a 33uf capacitor.

Reed,

I checked C1304 and it is fine, measures 2.7uf on the dot. CR1304 was replaced with a IN4007 per your recommendation and I tried your test to the base of Q1318.

The first time I taped the base of Q1318 with a 1K resistor in series with the +5 volt rail the waveform at TP1318 more than doubled in amplitude from 760mv p-p to 2.2 volts p-p and has stayed there. The frequency however, is now down to 14.4Khz

Now when I touch the lead of the 1K resistor from the +5 volt rail to the base of Q1318 the Oscillator waveform at TP1318 jumps up to 7.2 volts p-p still at 14.4 Khz. When I take the 1K resistor away the waveform drops back to 2.2 volts.

BREAKING NEWS:

While typing this report up I turned back to the scope, taped the 1K resistor from the +5 volt rail to the base of Q1318 again. This time the waveform at TP1318 jumped up to 30.8 volts p-p and now I have a trace on the CRT. Take the 1K resistor away and the waveform at TP1318 keeps running at 30.8 volts p-p and there is still a trace on the CRT. Note: The trace is only covering about a two-thirds of the screen and the horizontal position is behaving strange. Instead of sliding the whole trace left or right. It erases part of trace moving towards the middle of the screen if the Horizontal position is turn left or right. I suspect that is because the HV oscillator is only running at 13.8Khz.

I shut the scope off then turn it back on. The waveform at TP1318 is down to 2.2 volts p-p. Tap the base of Q1318 with the lead from the 1k resistor going to +5 volt rail and the oscillator waveform is goosed to 30.8 volts p-p again. The trace on the CRT is present as before and stays there until I shut the scope off and turn it back on.

How weird is that!

So now what? Is Q1318 flaky? I kind of doubt that. C1316 was replaced with a new 1uf tantalum capacitor. C1317 was pulled and checked. The LCR meter says it’s a 10uf capacitor. I don’t remember what the ESR was but I don’t remember it raising an eyebrow with me. CR1317 was check with the diode function on my HP 3466 DMM but it could be leaky…maybe?

What the Heck?

Ripley

Sent from Mail for Windows 10

From: Steph L
Sent: Saturday, March 2, 2019 5:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 475 with no Display and no HV

Page 3-35 of manual has a good functional description including point that ambient current supplied to base (of Q1318) determines frequency (ie not LC arrangement) and as such there isn’t a specific cap component for resonate frequency (a function oscillator still relies upon however to function).

You said “The rest of the voltage measurement compared to the manual are no where near correct” so perhaps a closer look at the whole setup noting Q1308/10 push-pull, gain and phase reversal Q1306 and bias arrangement behind Q1310 (ie the Q1312 and associated components).

I have an old Tek544 where the HT falls dramatically when ambient room temp too hot and was amazed in the frequency shift involved.

It is a different circuit but 475 still has resonance involved and the output voltage is regulated by driving current harder into the base.

Just a thought. Please excuse me/any error as nubie here. Interesting fault.








Re: 2247A PSU Troubleshooting

 

On Mon, Mar 4, 2019 at 12:17 AM, Nicholas Keller wrote:


I measured 120-122VAC up to the diode ring. Does this
suggest that C2202 is bad?
I guess you realise you're measuring in an area that is directly connected to the mains, no isolation? Take great care! *Do* use an isolation transformer and *float your 2247A*.

Did you measure the 77 V across C2202 or between C2202 and chassis? The latter would be incorrect, because the chassis is floating (with exception of some C's) against C2202 (since that has a galvanic coupling to the mains).

Raymond

Re: 2465-erratic cursors

Chuck Harris
 

Is it an actual 2465, or the A or B model?

I ask because the actual 2465 uses a very funny
pot for the Delta controls. It has no stop, a
conventional resistor wafer, but two separate
wipers that ride on the resistor wafer with an offset.
The program watches the voltages out of the two wipers
change as you rotate the control, and calculates the
position of the cursors... which takes a little time.

Anyway, pots get dirty, and need a little lube from
time to time.... Especially pots that get cranked on
as much as the cursor pots do. There really is nothing
much else it could be... especially if other pots are
not affected.

If you have the A or B model scope, the CPU is over
taxed by all the stuff that has to be cyclically checked
and dealt with, and that causes a delay between when
you turn a knob and when it makes the function happen.

And, all three scopes will get a little put out when you
turn a knob more quickly than the CPU can process the
info and make its response.

-Chuck Harris

@DC912 wrote:

The Delta Ref and Delta pots on my 2465 are very erratic (both cursors jump around when the pots are turned whether in independent or tracking mode), but all of the other pots on the front panel seem to work fine. Any troubleshooting suggestions would be appreciated. Thanks. Dave



Re: 475 with no Display and no HV

Steph L
 

Hi Ripley,
How about C1305 0.1uF.
If open, gain of Q1306 (and whole oscillator loop) will be lower and perhaps not enough to maintain oscillation? (Great suggestion from Don re 1K pull up touch on Q1318 base.)
Steph

PS. Still nubie here and unsure which "Reply" button to click on. I clicked on Ripley's "what the heck?" message "reply" button and see it has been inserted a few messages prior! That is really confusing. I'm in Melbourne Oz GMT +10 hrs. Is this the reason (i mean time difference guys and not quirky)

Re: 475 with no Display and no HV

SuddenLink
 

Hi Steph,

You are doing fine. I am getting all of your responses and may I add, it is much appreciated at this end.

Ripley

Sent from Mail for Windows 10

From: Steph L
Sent: Sunday, March 3, 2019 7:05 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 475 with no Display and no HV

Hi Ripley,
How about C1305 0.1uF.
If open, gain of Q1306 (and whole oscillator loop) will be lower and perhaps not enough to maintain oscillation? (Great suggestion from Don re 1K pull up touch on Q1318 base.)
Steph

PS. Still nubie here and unsure which "Reply" button to click on. I clicked on Ripley's "what the heck?" message "reply" button and see it has been inserted a few messages prior! That is really confusing. I'm in Melbourne Oz GMT +10 hrs. Is this the reason (i mean time difference guys and not quirky)

Re: 475 with no Display and no HV

SuddenLink
 

Hello Again,

I went back to the circuit around Q1306 and Q1308 this evening. The resistors are all within specs. C1305 was pulled and checked. It is also fine. C1304 is good and so is C1302.
By the way I am checking the capacitors with a DE-5000 LCR meter. It was never let me down yet.

The only component that I have not replaced or substituted is Q1306. It checks fine on my little Chinse component tester. For whatever that is worth.

Enough for today.

Ripley

Sent from Mail for Windows 10

From: Steph L
Sent: Sunday, March 3, 2019 7:05 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 475 with no Display and no HV

Hi Ripley,
How about C1305 0.1uF.
If open, gain of Q1306 (and whole oscillator loop) will be lower and perhaps not enough to maintain oscillation? (Great suggestion from Don re 1K pull up touch on Q1318 base.)
Steph

PS. Still nubie here and unsure which "Reply" button to click on. I clicked on Ripley's "what the heck?" message "reply" button and see it has been inserted a few messages prior! That is really confusing. I'm in Melbourne Oz GMT +10 hrs. Is this the reason (i mean time difference guys and not quirky)

Re: Help with 7A18 problem

Phillip Potter
 

Hi Bill,

No... There was nothing that I wrote that I think is wrong. It was a matter of timing.  I hadn't read all of the other replies, especially the one where you found the attenuator pin issue!

I felt that my reply was badly timed and didn't add to the conversation.  I did, however, tear my 7A18 down and clean the switch fingers with IPO, and got it all back together; whew!  So, from that aspect, it was ok.

I hope that I haven't led you astray or been a bad influence, Bill... and I wish you the best with your amplifiers!

Phil

On 3/3/2019 2:31 PM, Bill Carns wrote:
What ?? Now confused. Was there something wrong with your first reply?

Bill

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Phillip Potter
Sent: Sunday, March 03, 2019 3:46 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with 7A18 problem

Please disregard!!!

Sorry,

Phil

On 3/3/2019 1:38 PM, Phillip Potter wrote:
Hi Bill,

I have the same amplifiers and when I first got them, had the same or
at least similar issues.

I tore them down, one at a time, and soaked 24lb bond with IPA, to
clean those switches. Yes, they are a bear to get to! IIRC, I had to
disassemble them down a ways to get into them. There were shields on
the inner sides and on the outer sides, too. Once I had them broken
down, it was a simple thing to get the soaked paper into the switch
fingers and carefully pull it through, in the same way that a
turntable moves a record under the stylus... never backward!

I recommend doing this somewhere where you can leave it laying,
disassembled, so that you can see how you got it apart, making it
easier to reassemble it. I took pictures on my phone at each step of
the way. It was a "trick" of a deal getting it broken down to the
point where it could be cleaned, however. Pictures helped me to stay
on track and get it all back together! Tektronix did it's homework...
they were made to be repaired... gotta love 'em!

I hope I've inspired you and not the opposite. I did have to work up
my nerve to tear into them, but the result was two operable
amplifiers, I am glad that I took my time and worked carefully.

Phil

On 3/2/2019 2:26 PM, Bill Carns wrote:
I'll have to go put the unit back in the mainframe and investigate
but my memory says that most were bad.

I have investigated more and remove the upper capacitor cover and,
boy are those things hard to get at. Gonna be real hard to get
cleaning paper in there on all the switches. Some are not bad,
others really bad to get to. One set has an additional little cover
over them for some reason.

Working on this thing is not for sissies.


B

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Albert Otten
Sent: Saturday, March 02, 2019 3:53 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with 7A18 problem

On Sat, Mar 2, 2019 at 07:58 PM, Colin Herbert wrote:

---
On the subject of the input attenuators, they are the type which are
operated by cam-switches. They have springy gold-plated contacts
that get moved up-and-down by cams on the controls shaft. The
circuit board that they are on has gold-plating, too, and the board
itself is made of an easily-damaged material. You need to use thin
strips of paper moistened in IPA and trapped between the moving and
stationary contacts, they *gently* pulling the paper strip out. You
may have to do this a few times. Don't use any other solvents or
contact-cleaner as you will probably ruin the board. Of course it
may only be one or two of these contacts that is dirty, as has
already been suggested; there are only four attenuators there - they
get switched in-and-out to get the different VOLTS/DIV settings. In
the most sensitive VOLTS/DIV setting, they are all switched out, so
if your 5mV/div setting shows lousy bandwidth, then it is likely to
be caused by some other problem, not just the attenuators and their
switching . Of course, there might be a problem there, too, but it
won't be the only one.
Hi Colin,

You probably were too quick in your statement about the 5 mV/div
setting. In that setting all attenuators are bypassed by means of a
series of closed contacts, so any dirty contacts there destroy the
signal path.
I'm not sure about the 7A18 construction. My impression is that
including AC/DC there are 10 contact pairs above the drum and 10
below the drum. (Each contact pair forming one switch).

It would still be nice to hear from Bill which V/div settings are
good and which are bad.

Albert










Re: 2247A PSU Troubleshooting

Nicholas Keller
 

No, I was not using an isolation transformer (I don’t have one) and yes I
was measuring between cap and chassis. I will look into getting a
transformer before testing across c2202 or doing other troubleshooting.

Thanks for the warning

Nick


On Sun, Mar 3, 2019 at 6:49 PM Raymond Domp Frank <@Raymond>
wrote:

On Mon, Mar 4, 2019 at 12:17 AM, Nicholas Keller wrote:


I measured 120-122VAC up to the diode ring. Does this
suggest that C2202 is bad?
I guess you realise you're measuring in an area that is directly connected
to the mains, no isolation? Take great care! *Do* use an isolation
transformer and *float your 2247A*.

Did you measure the 77 V across C2202 or between C2202 and chassis? The
latter would be incorrect, because the chassis is floating (with exception
of some C's) against C2202 (since that has a galvanic coupling to the
mains).

Raymond



Re: Help with 7A18 problem

Bill Carns
 

My thanks and I got some good encouragement and experience from your post - Thanks.

Bill

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Phillip Potter
Sent: Sunday, March 03, 2019 7:46 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with 7A18 problem

Hi Bill,

No... There was nothing that I wrote that I think is wrong. It was a matter of timing. I hadn't read all of the other replies, especially the one where you found the attenuator pin issue!

I felt that my reply was badly timed and didn't add to the conversation. I did, however, tear my 7A18 down and clean the switch fingers with IPO, and got it all back together; whew! So, from that aspect, it was ok.

I hope that I haven't led you astray or been a bad influence, Bill...
and I wish you the best with your amplifiers!

Phil

On 3/3/2019 2:31 PM, Bill Carns wrote:
What ?? Now confused. Was there something wrong with your first reply?

Bill

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Phillip Potter
Sent: Sunday, March 03, 2019 3:46 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with 7A18 problem

Please disregard!!!

Sorry,

Phil

On 3/3/2019 1:38 PM, Phillip Potter wrote:
Hi Bill,

I have the same amplifiers and when I first got them, had the same or
at least similar issues.

I tore them down, one at a time, and soaked 24lb bond with IPA, to
clean those switches. Yes, they are a bear to get to! IIRC, I had
to disassemble them down a ways to get into them. There were shields
on the inner sides and on the outer sides, too. Once I had them
broken down, it was a simple thing to get the soaked paper into the
switch fingers and carefully pull it through, in the same way that a
turntable moves a record under the stylus... never backward!

I recommend doing this somewhere where you can leave it laying,
disassembled, so that you can see how you got it apart, making it
easier to reassemble it. I took pictures on my phone at each step of
the way. It was a "trick" of a deal getting it broken down to the
point where it could be cleaned, however. Pictures helped me to stay
on track and get it all back together! Tektronix did it's homework...
they were made to be repaired... gotta love 'em!

I hope I've inspired you and not the opposite. I did have to work up
my nerve to tear into them, but the result was two operable
amplifiers, I am glad that I took my time and worked carefully.

Phil

On 3/2/2019 2:26 PM, Bill Carns wrote:
I'll have to go put the unit back in the mainframe and investigate
but my memory says that most were bad.

I have investigated more and remove the upper capacitor cover and,
boy are those things hard to get at. Gonna be real hard to get
cleaning paper in there on all the switches. Some are not bad,
others really bad to get to. One set has an additional little cover
over them for some reason.

Working on this thing is not for sissies.


B

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Albert Otten
Sent: Saturday, March 02, 2019 3:53 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with 7A18 problem

On Sat, Mar 2, 2019 at 07:58 PM, Colin Herbert wrote:

---
On the subject of the input attenuators, they are the type which
are operated by cam-switches. They have springy gold-plated
contacts that get moved up-and-down by cams on the controls shaft.
The circuit board that they are on has gold-plating, too, and the
board itself is made of an easily-damaged material. You need to use
thin strips of paper moistened in IPA and trapped between the
moving and stationary contacts, they *gently* pulling the paper
strip out. You may have to do this a few times. Don't use any other
solvents or contact-cleaner as you will probably ruin the board. Of
course it may only be one or two of these contacts that is dirty,
as has already been suggested; there are only four attenuators
there - they get switched in-and-out to get the different VOLTS/DIV
settings. In the most sensitive VOLTS/DIV setting, they are all
switched out, so if your 5mV/div setting shows lousy bandwidth,
then it is likely to be caused by some other problem, not just the
attenuators and their switching . Of course, there might be a
problem there, too, but it won't be the only one.
Hi Colin,

You probably were too quick in your statement about the 5 mV/div
setting. In that setting all attenuators are bypassed by means of a
series of closed contacts, so any dirty contacts there destroy the
signal path.
I'm not sure about the 7A18 construction. My impression is that
including AC/DC there are 10 contact pairs above the drum and 10
below the drum. (Each contact pair forming one switch).

It would still be nice to hear from Bill which V/div settings are
good and which are bad.

Albert











Re: 2465-erratic cursors

@DC912
 

Thanks Chuck. It's the 2465, not A or B. Can these pots be cleaned like a traditional pot, or are they sealed?

Re: 2465-erratic cursors

Chuck Harris
 

They are a modular pot that can be disassembled
by removing a pair of micro torx screws from the
back side, and popping off the back.

Use something like DeOxit Fader Lube.

-Chuck Harris

@DC912 wrote:

Thanks Chuck. It's the 2465, not A or B. Can these pots be cleaned like a traditional pot, or are they sealed?



Re: 577 whine with variable collector

DW
 

I believe this could be a characteristic of this instrument, I watched a video from YouTube CuriousMarc - Tektronix 577 repair and Demo. Carefully watching that video with the variable collector set low I notice the interference pattern on the trace which goes away when the collector voltage is turned higher, this is exactly what I experience.

Re: PG 506

Jean-Paul
 

Hello Jim: The extender costs are high, and some plugins need several connectors.

I have fixed many TM500 modules by taking a 1-2-3-4 wide mainframe and removing all the covers.

A 1 wide plugin in a single mainframe and 2 wide in a 2 plugin mainframe is ideal, as you have access to every side.

You can still get the PC card edge connectors and DIY.

Kind Regards,

Jon

Re: Tektronix 2440 Fails DTE External Calibration. Any ideas?

Miguel Work
 

CCD ...

-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Rich Gill
Enviado el: domingo, 3 de marzo de 2019 1:37
Para: TekScopes@groups.io
Asunto: [TekScopes] Tektronix 2440 Fails DTE External Calibration. Any ideas?

Instructions is Service Manual leave a little to be understood.

Manual Says:
d: Connect a FAST RISE OUTPUT of a Calibration Generator to the CH1 and CH2 input connectors through a 50-ohm cable,a 5 x attenuator, and a dual input coupler.
(I have a Tektronix PG506 Calibration Generator).
e: Set the Calibration Generator for FAST RISE output at a 100khz frequency. Set the generator amplitude to maximum.

I get error message after i press EXCUTE (Frequency to fast if over 75KHz)

It excute for 20 -30 minuets and then Fails Code 7300, 7310, 7320.

Anyone have a ideas what I am doing wrong.

Tnx