Date   

Re: 7B50 - No Trace

n4buq
 

Ozan,

I'm not sure, but I may have made some mistakes in those voltage measurements (conflated one resistor with another) because I checked the voltage across L267 and it is nearly zero.

I just did a bit of looking further down the signal path and found that the base of Q305 is about -0.5V instead of +0.27V as shown on the schematic. I suspected Q293 might be responsible (in part) for that and I pulled it. It checks "ok" on my component tester; however, with it out of the circuit, the base of Q305 is now a bit closer to the positive value on the schematic. I think it's around 0.5V but I didn't write that down so I'd have to check for a more precise value.

At any rate, with Q293 out, I now get what appears to be a single-shot trace. At a slow sweep speed (e.g. 1s/div) I can switch the display mode to AMPLIFIER and then back to TIME-BASE and can see two dots moving across the screen (using the calibrator as input so two dots makes sense). This isn't the case with Q293 in place.

Am I chasing a ghost or is it possible there's a problem with Q293 that my component checker doesn't reveal? Note that CR299 is also at play at the base of Q305 and I'm now wondering if that might be part of the problem.

BTW, I put a 220-ohm across R394 which brought it down to 50-ohms but that didn't seem to change anything. I'm wondering what the true values of the decoupled voltages should be. The schematic simply shows them as their standard values (e.g. +15, -15, etc.) and I'm not sure what should be the correct values. I haven't found anything in the manual that defines that either.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Tuesday, November 16, 2021 11:19:07 AM
Subject: Re: [TekScopes] 7B50 - No Trace
On Mon, Nov 15, 2021 at 01:55 PM, n4buq wrote:
I think I discovered where R394 and C395 are. They're in plain sight just on
the other side of a metal shield - just across from R264. The parts layout
image labels those as R265 and C264; however there are no such parts (at least
not that I can find) in the parts list and I could not find those numbers on
the schematic either.
Good detective work.

In any case, R394 measures 65 ohms so I'll be looking to replace that. I
probably should replace the electrolytics in the decoupling section just for
good measure.
Although I agree R394 looks a little too high and changing it should help, it is
unlikely the root cause of the fault you are seeing.

Your measurement of voltage difference between bottom of R264 and base of Q266
needs another look. We don't expect so much DC drop across L267. Another data
point is voltage across CR262 was 0.249V and voltage across R267 is 0.47V that
again says there is some DC drop across L267.
Ozan



Re: 7B50 - No Trace

Ozan
 

On Mon, Nov 15, 2021 at 01:55 PM, n4buq wrote:
I think I discovered where R394 and C395 are. They're in plain sight just on
the other side of a metal shield - just across from R264. The parts layout
image labels those as R265 and C264; however there are no such parts (at least
not that I can find) in the parts list and I could not find those numbers on
the schematic either.
Good detective work.

In any case, R394 measures 65 ohms so I'll be looking to replace that. I
probably should replace the electrolytics in the decoupling section just for
good measure.
Although I agree R394 looks a little too high and changing it should help, it is unlikely the root cause of the fault you are seeing.

Your measurement of voltage difference between bottom of R264 and base of Q266 needs another look. We don't expect so much DC drop across L267. Another data point is voltage across CR262 was 0.249V and voltage across R267 is 0.47V that again says there is some DC drop across L267.
Ozan


Re: Tek 575 Mod Lit Redone

 

Thank you so much for doing that! I just brought home a 575 yesterday. It runs perfect at the moment. My 576 acts up sometimes, so it will be a nice back up.


Re: Removing the Adhesive From Hell

bill koski
 

CRC Brakleen in the red can works well on many adhesives. Also a very good degreaser. It doesn't hurt most rubber parts and fine on any raw metal parts. Some paints it's OK with others it will attack. OK with most plastics. So test before use.
I usually spray it on a rag and use that to rub off the crud especially if it's a possibly sensitive area. It evaporates quickly.


Re: 7704A - Grid Bias

Albert Otten
 

I agree with Barry's comments, the time base setting of the test scope is not specified at all. Why not leave that setting at fast speed all the time, like done for the ground reference? [BTW: Where is that large hold-off (?) time coming from?] Later on In the video, while judging "just visible", the 7704A is apparently set at much faster speed than the prescribed 0.2 s/div. When I understand the Rigol readout correctly, it's more like 10 ms per sweep or 1 ms/div.

Barry, even with Intensity fully CCW the TP voltage still switches between two levels, unblanked and blanked. A DMM can be used when its settling time is well within a trace time, here 2 s.Then the unblanked TP voltage can be read and increased by 4 V.
BTW: the procedure simply talks about "the" TP DC level which in my opinion has to be read as the unblanked level..

Albert


Re: 7704A - Grid Bias

n4buq
 

Oops! I didn't realize the video was yours(?). I still don't see where setting the test scope's timebase to 0.2s/div accomplishes anything for measuring the voltage on it. In fact, I don't understand why the test scope is needed and a digital volt meter would work. I know I must be missing something...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: Zentronics42@...
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, November 15, 2021 6:55:51 PM
Subject: Re: [TekScopes] 7704A - Grid Bias
Barry,
I have tried for a while to get the setting copied here but PDF's just wont
cooperate with me at the moment. The YouTube video is the correct procedure
based on the service manual. You could easily do this same procedure based on
X-Y mode as well however you will be stuck when you get to step 6 transient
response. This will need a moving sweep of about 10 Mhz. What they mean in the
manual by free running sweep is the time base in auto untriggered. This means
that you do NOT need the calibrator a 7aX set to GND on the input would be
fine. But this does lead me to another question. If step 6 is transient
response, do you have brightness issues with A sweep at faster time base
settings? Relevant pages in the service manual are 4-7 and 4-8

Then manual just does the grid bias with a moving untriggered sweep and them
moves right in to transient response. This set up allows you to go both
adjustments with out having to reconfigure the test set up. The digital scope
used in the video was to get the +4v set point as well as the transient
response. Sorry about the confusion. This is what I get for trying to do things
from memory at this point.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of n4buq
Sent: Monday, November 15, 2021 9:46 AM
To: tekscopes <TekScopes@groups.io>
Subject: Re: [TekScopes] 7704A - Grid Bias

Zen,

Regarding that calibration video, I notice the fellow is setting the timebase in
the "test" oscilloscope to 0.2s/div. That doesn't make sense to me and I
presume it's incorrect. He switches to a digital scope to measure the +4V
delta but the image on the 7704A is a line, not a dot. I don't suppose it
really matters exactly what's displayed but I presume the timebase in the 7704A
is not set per the instructions(?).

Thanks,
Barry - N4BUQ

----- Original Message -----
From: Zentronics42@...
To: "tekscopes" <TekScopes@groups.io>
Sent: Sunday, November 14, 2021 8:06:21 PM
Subject: Re: [TekScopes] 7704A - Grid Bias
Barry a question about the setup. Do you have any plugins in the frame
at all when you are attempting to do the grid bias setting? No plugins
will not give the tube any drive signals so there will be no dot. The
Easiest way to get a dot on a 7704A is to use 2 vertical plugins one
in vert one in horz. This will put the frame in to X-Y mode and should
give you a display that is adjustable from the controls. That is how I
would do grid bias with out the standardizer, but your milage may vary.

This might also help if you have not seen this it is a full
calibration on a 7704A https://www.youtube.com/watch?v=16QHePfnkHk

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jeff
Dutky
Sent: Sunday, November 14, 2021 8:34 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7704A - Grid Bias

Barry,

I have not been able to find my notes on the grid bias problem I saw
in the 475A, but here is the thread on the subject, which will be
nearly as good as my
notes:

https://groups.io/g/TekScopes/topic/grid_bias_adjustment_on_475a/79348
510?p=Created%2C%2C%2C20%2C2%2C120%2C0&jump=1

The problem was that I could barely get the spot to show up during the
grid bias adjustment process, and the grid bias trim pot was cranked
all the way over to one end of its range, so there was no room for
further adjustment, and adjusting in the only direction available to
me would completely quench to spot, so it wasn't useful.

The solution, after various investigations, turned out to be the HV
precision resistor that was used to regulate the HV multiplier output.
Replacement of that resistor fixed the problem (though it may have
been possible to fix the problem merely by thoroughly cleaning and
resoldering the resistor, but I never went back and tried that). The
main difference between my problem and yours, however, was that I was
NOT seeing high CRT brightness. If anything the CRT brightness was a little low.

-- Jeff Dutky
















Re: TEK 5111A

Roy Morgan <k1lky68@...>
 

Just add the "R" to the name. All done.

Roy Morgan
K1LKY Western Mass

On Nov 15, 2021, at 8:01 PM, byterock@... wrote:


ok 'R' for rack I would take it.

This is what I thought


Re: TEK 5111A

byterock@...
 

ok 'R' for rack I would take it.

This is what I though

Cheers
John


Re: 7704A - Grid Bias

Zentronics42@...
 

Barry,
I have tried for a while to get the setting copied here but PDF's just wont cooperate with me at the moment. The YouTube video is the correct procedure based on the service manual. You could easily do this same procedure based on X-Y mode as well however you will be stuck when you get to step 6 transient response. This will need a moving sweep of about 10 Mhz. What they mean in the manual by free running sweep is the time base in auto untriggered. This means that you do NOT need the calibrator a 7aX set to GND on the input would be fine. But this does lead me to another question. If step 6 is transient response, do you have brightness issues with A sweep at faster time base settings? Relevant pages in the service manual are 4-7 and 4-8

Then manual just does the grid bias with a moving untriggered sweep and them moves right in to transient response. This set up allows you to go both adjustments with out having to reconfigure the test set up. The digital scope used in the video was to get the +4v set point as well as the transient response. Sorry about the confusion. This is what I get for trying to do things from memory at this point.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of n4buq
Sent: Monday, November 15, 2021 9:46 AM
To: tekscopes <TekScopes@groups.io>
Subject: Re: [TekScopes] 7704A - Grid Bias

Zen,

Regarding that calibration video, I notice the fellow is setting the timebase in the "test" oscilloscope to 0.2s/div. That doesn't make sense to me and I presume it's incorrect. He switches to a digital scope to measure the +4V delta but the image on the 7704A is a line, not a dot. I don't suppose it really matters exactly what's displayed but I presume the timebase in the 7704A is not set per the instructions(?).

Thanks,
Barry - N4BUQ

----- Original Message -----
From: Zentronics42@...
To: "tekscopes" <TekScopes@groups.io>
Sent: Sunday, November 14, 2021 8:06:21 PM
Subject: Re: [TekScopes] 7704A - Grid Bias
Barry a question about the setup. Do you have any plugins in the frame
at all when you are attempting to do the grid bias setting? No plugins
will not give the tube any drive signals so there will be no dot. The
Easiest way to get a dot on a 7704A is to use 2 vertical plugins one
in vert one in horz. This will put the frame in to X-Y mode and should
give you a display that is adjustable from the controls. That is how I
would do grid bias with out the standardizer, but your milage may vary.

This might also help if you have not seen this it is a full
calibration on a 7704A https://www.youtube.com/watch?v=16QHePfnkHk

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jeff
Dutky
Sent: Sunday, November 14, 2021 8:34 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7704A - Grid Bias

Barry,

I have not been able to find my notes on the grid bias problem I saw
in the 475A, but here is the thread on the subject, which will be
nearly as good as my
notes:

https://groups.io/g/TekScopes/topic/grid_bias_adjustment_on_475a/79348
510?p=Created%2C%2C%2C20%2C2%2C120%2C0&jump=1

The problem was that I could barely get the spot to show up during the
grid bias adjustment process, and the grid bias trim pot was cranked
all the way over to one end of its range, so there was no room for
further adjustment, and adjusting in the only direction available to
me would completely quench to spot, so it wasn't useful.

The solution, after various investigations, turned out to be the HV
precision resistor that was used to regulate the HV multiplier output.
Replacement of that resistor fixed the problem (though it may have
been possible to fix the problem merely by thoroughly cleaning and
resoldering the resistor, but I never went back and tried that). The
main difference between my problem and yours, however, was that I was
NOT seeing high CRT brightness. If anything the CRT brightness was a little low.

-- Jeff Dutky









Re: Type 531 parting out

wallace.dg@...
 

I reside in Georgia.

Davis


Re: Older current probes with newer amplifiers?

Xu Wang
 

Another problem is to figure out how the checksum is calculated. That would pave the way for us to generate meaningful data set. Without it, even simple changes to the serial number will make the data unusable.


Re: Removing the Adhesive From Hell

Geoffrey Thomas
 

On 15/11/2021 22:17, Geoffrey Thomas via groups.io wrote:
Iso-propyl alcohol (IPA) may be less reactive, but again try on a small area first.
Geoff.
On 15/11/2021 19:50, Greg Muir via groups.io wrote:
I’ve had varying success with all of the “popular” methods of removing dried masking tape adhesive.  Most leave you still with a cleanup job at best.

The best approach I have found is using ethyl alcohol (ethanol).  Even applying over the masking tape if it still remains soaks through the paper backing and loosens the adhesive but the best method is to remove the tape first if you can.  Be patient and keep the adhesive wet to allow the alcohol to do its job.  Then periodically wipe away the part that has softened repeating a few times until the adhesive is gone.  I often get inpatient and use my thumbnail to scrape the softened adhesive to speed the process along.  Using the edge of an old credit card will also do the trick.

A word of caution – ethyl alcohol will soften some paints and attack some plastics.  It’s best to try it on a small spot to see if the surface is safe to apply the alcohol.  I have found the paint used on the cast frame that surrounds the front panels of earlier HP equipment has a tendency to be softened by the alcohol.

A sidebar - when working for one large organization that had its own internal construction department I asked the head painter about what he used to remove unwanted latex paint.  He told me that ethyl alcohol was his standard product.  I tried it and found ti to be 100% effective at the job.

Greg


Re: Removing the Adhesive From Hell

Geoffrey Thomas
 

Iso-propyl alcohol (IPA) may be less reactive, but again try on a small area first.

Geoff.

On 15/11/2021 19:50, Greg Muir via groups.io wrote:
I’ve had varying success with all of the “popular” methods of removing dried masking tape adhesive. Most leave you still with a cleanup job at best.
The best approach I have found is using ethyl alcohol (ethanol). Even applying over the masking tape if it still remains soaks through the paper backing and loosens the adhesive but the best method is to remove the tape first if you can. Be patient and keep the adhesive wet to allow the alcohol to do its job. Then periodically wipe away the part that has softened repeating a few times until the adhesive is gone. I often get inpatient and use my thumbnail to scrape the softened adhesive to speed the process along. Using the edge of an old credit card will also do the trick.
A word of caution – ethyl alcohol will soften some paints and attack some plastics. It’s best to try it on a small spot to see if the surface is safe to apply the alcohol. I have found the paint used on the cast frame that surrounds the front panels of earlier HP equipment has a tendency to be softened by the alcohol.
A sidebar - when working for one large organization that had its own internal construction department I asked the head painter about what he used to remove unwanted latex paint. He told me that ethyl alcohol was his standard product. I tried it and found ti to be 100% effective at the job.
Greg


Re: TEK 5111A

 

Yes, this is just a rearrangement of the scope for rack mounting. Technically you might call this an R5111A, but it was easy to convert a desktop 5111A to a rack mount unit (and vice versa), with just a few extra parts (e.g. the metal side panels on the desktop unit are replaced with different top and bottom panels in the rack mount configuration), so it's perfectly likely that someone did this to a 5111A and did not alter the badging.

-- Jeff Dutky


Re: 7B50 - No Trace

n4buq
 

Make that "I think I discovered where R394 and C394 are."

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, November 15, 2021 3:55:49 PM
Subject: Re: [TekScopes] 7B50 - No Trace
I think I discovered where R394 and C395 are. They're in plain sight just on
the other side of a metal shield - just across from R264. The parts layout
image labels those as R265 and C264; however there are no such parts (at least
not that I can find) in the parts list and I could not find those numbers on
the schematic either. You can see those about mid-way vertically and to the
left side in the image for the Trigger Generator (next to Q315 on Figure 4-4).
Apparently the schematic folks and the manual folks got something out of
sync(?).

In any case, R394 measures 65 ohms so I'll be looking to replace that. I
probably should replace the electrolytics in the decoupling section just for
good measure. If those are leaking, then it would further explain excessive
voltage losses due to the drops across R393, R394, and R395.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Barry" <n4buq@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Sunday, November 14, 2021 4:07:34 PM
Subject: Re: [TekScopes] 7B50 - No Trace
Hi Ozan,

Here are the voltages at the various points:

First off, the PS voltages and their decoupled voltages:
50.0V/49.7V
-50.0V/-49.8V
14.98V/14.36V (DCPL #1)
14.98V/13.18V (DCPL #2)
-15.0V/-14.45V

I did not have triggering enabled for TP262's or Q266's readings.

TP262: 12.64V

Q266:
C: 5.5V
B: 13.3V
E: 13.96V

Top of R264: 13.18V
Bottom of R264: 13.02V

0.47V across R267

I'm wondering whether DCPL #2 (or #1 for that matter) are too low. I can
measure 65 ohms from the top of R264 to +15 DCPL #1 which indicates R394 has
gone high; however, I cannot find R394 (or C394 either) on the board or on the
drawing in the manual. If you know where those two are hiding out, I would
love to know where they are.

Does any of the above give rise to any concern for you or, even better, point to
a possible problem point?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Saturday, November 13, 2021 2:58:49 PM
Subject: Re: [TekScopes] 7B50 - No Trace
Hi Barry,
My comments are below.

On Sat, Nov 13, 2021 at 10:56 AM, n4buq wrote:

With a 10x probe, DC coupling, and the lamp indicator showing 5V/DIV, the
square wave at TP262 toggles between 11V and about 12.5V. That's somewhat
...
I have this plugin but the mainframe is not on my bench so my comments are based
on the schematic, not the actual measurements. Looking at the schematic
voltages, Q254 collector is at 12.65V DC, TP262 should be one diode (1N4152)
above that so we expect DC at TP262 to be ~ 13.2V. Your measurement shows even
peaks are not exceeding 12.5V. Something to keep in mind during debug.


Switching the 465B to 1V/DIV and AC coupling, I can see that the waveform at
TP262 has a delta voltage of 1.3V.
I calculated Q254/Q244 collector currents to be about 5mA so 10mA-peak-to-peak
feeding to TP262 is consistent with your ~ 1.3Vpp signal.

The voltage on the other side of R262 is
at nearly the same vertical offset (~11V) but the delta voltage is 0.5V.

The DC voltage across CR262 is 0.249V.
Anode of CR262 is connected to +15V DCPL#2 with a small resistor. If CR262 only
drops 0.249V we expect 14-14.7V at the cathode. However, your measurement is
showing only ~ 11V. Right side of R262 and cathode of CR262 should have same DC
voltage.

I would try to sort out the voltage drops first, starting at +15V DCPL#2 and
going towards TP262:
What voltage (DC is OK, actual tops and bottoms is useful) do you see at the top
of R264, at anode of CR262, cathode of CR262, right side of R262?

Just in case Q266 is bad and base is stealing current: what voltages do you see
at B/E/C of Q266?
Ozan






Re: 7B50 - No Trace

n4buq
 

I think I discovered where R394 and C395 are. They're in plain sight just on the other side of a metal shield - just across from R264. The parts layout image labels those as R265 and C264; however there are no such parts (at least not that I can find) in the parts list and I could not find those numbers on the schematic either. You can see those about mid-way vertically and to the left side in the image for the Trigger Generator (next to Q315 on Figure 4-4). Apparently the schematic folks and the manual folks got something out of sync(?).

In any case, R394 measures 65 ohms so I'll be looking to replace that. I probably should replace the electrolytics in the decoupling section just for good measure. If those are leaking, then it would further explain excessive voltage losses due to the drops across R393, R394, and R395.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Barry" <n4buq@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Sunday, November 14, 2021 4:07:34 PM
Subject: Re: [TekScopes] 7B50 - No Trace
Hi Ozan,

Here are the voltages at the various points:

First off, the PS voltages and their decoupled voltages:
50.0V/49.7V
-50.0V/-49.8V
14.98V/14.36V (DCPL #1)
14.98V/13.18V (DCPL #2)
-15.0V/-14.45V

I did not have triggering enabled for TP262's or Q266's readings.

TP262: 12.64V

Q266:
C: 5.5V
B: 13.3V
E: 13.96V

Top of R264: 13.18V
Bottom of R264: 13.02V

0.47V across R267

I'm wondering whether DCPL #2 (or #1 for that matter) are too low. I can
measure 65 ohms from the top of R264 to +15 DCPL #1 which indicates R394 has
gone high; however, I cannot find R394 (or C394 either) on the board or on the
drawing in the manual. If you know where those two are hiding out, I would
love to know where they are.

Does any of the above give rise to any concern for you or, even better, point to
a possible problem point?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Saturday, November 13, 2021 2:58:49 PM
Subject: Re: [TekScopes] 7B50 - No Trace
Hi Barry,
My comments are below.

On Sat, Nov 13, 2021 at 10:56 AM, n4buq wrote:

With a 10x probe, DC coupling, and the lamp indicator showing 5V/DIV, the
square wave at TP262 toggles between 11V and about 12.5V. That's somewhat
...
I have this plugin but the mainframe is not on my bench so my comments are based
on the schematic, not the actual measurements. Looking at the schematic
voltages, Q254 collector is at 12.65V DC, TP262 should be one diode (1N4152)
above that so we expect DC at TP262 to be ~ 13.2V. Your measurement shows even
peaks are not exceeding 12.5V. Something to keep in mind during debug.


Switching the 465B to 1V/DIV and AC coupling, I can see that the waveform at
TP262 has a delta voltage of 1.3V.
I calculated Q254/Q244 collector currents to be about 5mA so 10mA-peak-to-peak
feeding to TP262 is consistent with your ~ 1.3Vpp signal.

The voltage on the other side of R262 is
at nearly the same vertical offset (~11V) but the delta voltage is 0.5V.

The DC voltage across CR262 is 0.249V.
Anode of CR262 is connected to +15V DCPL#2 with a small resistor. If CR262 only
drops 0.249V we expect 14-14.7V at the cathode. However, your measurement is
showing only ~ 11V. Right side of R262 and cathode of CR262 should have same DC
voltage.

I would try to sort out the voltage drops first, starting at +15V DCPL#2 and
going towards TP262:
What voltage (DC is OK, actual tops and bottoms is useful) do you see at the top
of R264, at anode of CR262, cathode of CR262, right side of R262?

Just in case Q266 is bad and base is stealing current: what voltages do you see
at B/E/C of Q266?
Ozan





TEK 5111A

byterock@...
 

Ok the scope says 5111A but all the pics of such of scope have the CRT sitting on top of 3 plugins. My newly acquired one has the RT on the left and 3 plug ins to the left.

Is this only a chassis difference?

What am I dealing with here.


Re: Removing the Adhesive From Hell

Greg Muir
 

I’ve had varying success with all of the “popular” methods of removing dried masking tape adhesive. Most leave you still with a cleanup job at best.

The best approach I have found is using ethyl alcohol (ethanol). Even applying over the masking tape if it still remains soaks through the paper backing and loosens the adhesive but the best method is to remove the tape first if you can. Be patient and keep the adhesive wet to allow the alcohol to do its job. Then periodically wipe away the part that has softened repeating a few times until the adhesive is gone. I often get inpatient and use my thumbnail to scrape the softened adhesive to speed the process along. Using the edge of an old credit card will also do the trick.

A word of caution – ethyl alcohol will soften some paints and attack some plastics. It’s best to try it on a small spot to see if the surface is safe to apply the alcohol. I have found the paint used on the cast frame that surrounds the front panels of earlier HP equipment has a tendency to be softened by the alcohol.

A sidebar - when working for one large organization that had its own internal construction department I asked the head painter about what he used to remove unwanted latex paint. He told me that ethyl alcohol was his standard product. I tried it and found ti to be 100% effective at the job.

Greg


Re: Removing the Adhesive From Hell

Jim Strohm
 

Try xylene on an inconspicuous area of the part.

I've had excellent results with this stuff on occasion... including on
those indestructible anti-slip stickers that get put in bathtubs.

I'm out of it now, and I don't have any cal tag or inventory tag residue to
try it on.

73
Jim N6OTQ


Re: Type 531 parting out

Dave Voorhis
 

If you're within a fifty mile radius of Derby, UK, I'll come get the lot if you're willing to part with it whole. Thanks!

I'm guessing you're not, though.

I mean, I'm guessing you're not within a fifty mile radius of Derby.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of wallace.dg@...
Sent: 15 November 2021 15:11
To: TekScopes@groups.io
Subject: [TekScopes] Type 531 parting out

I recently helped clean out a shop for a retired EE, and was given a Type 531 oscilloscope. It powers on, and the CRT shows a trace. However, I don't have any probes to determine functionality. At 60 some-odd pounds, this thing is a beast. Although the case is pretty rough, I will part it out, if anyone wants knobs, tubes, CRT, sub boards, etc.

Regards,
Davis

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