Date   

Re: Another A5 board repair attemp - help needed

Siggi
 

Hey Roger,

Outstanding, congrats on getting the traces going!
TEST04 means your calibration data is gone, and you'll have to re-calibrate
the scope. See pages 6-11/6-12 in the service manual. It's not the worst
thing in the world, as the scope probably could have done with a
calibration anyway.
I believe that the dots are unrelated to the calibration error, they're
likely there because your grid bias is too high (as Leo, satbeginner had
mentioned). This means you see the portions of the readout where the beam
should be blank. This probably also means that someone was in there before
you, but they only went so far as to tweak the grid bias.

Siggi

On Fri, Nov 6, 2020 at 1:30 PM Rogerio O <rodd414@gmail.com> wrote:

Progress!
I had already replaced R2012 but forgot to check R2013, which was open!
Both have been replaced with TE RN73C2B10KBTDF from Mouser (10K, 0.1%,
10ppm).
Now the scope boots with TEST4 FAIL2 but after pressing A/B TRIG the
horizontal lines is visible and the vertical position control work.
The next step is to find what is causing four dotted lines to appear near
the top and bottom of the display.
I have uploaded a photo of the display to the album related to this thread
(https://groups.io/g/TekScopes/album?id=256231).
Are they related to the error?
Thank you all for the help.
Roger






Re: Clean and Lubricate Pots in Tek 475

Ed Breya
 

Yes, getting the pots out may be the hardest part, whether you refurbish them or replace them. Again, I don't know how accessible they are, but at least they're on the periphery of the front panel. If the pots are those square black or blue "modular" type, with screws on the back, they can easily be opened up for cleaning and re-lubing. Just keep track of all the pieces as you go, and how they need to fit back together. Some of these pot types are riveted together rather than held with screws. Even these can be worked over by carefully drilling out the ends of the rivets, and replacing them with 2-56 screws, long enough to go through the assembly.

If it is just too much grief to get the pots out, and soaking the bushings isn't enough, there other tricks to help with getting more oil into them. If you have a well stocked parts/junk department, you may have some "pot spacers," which are typically hollow hex tubes of various lengths, threaded the same as the pot (1/4-30 or 1/4-32 I think). These are commonly used in equipment to recess pots behind the front panel. If you find one, you can remove the original pot nut, and thread the spacer on in its place, just a little more than hand tight. Then put the scope on its back with the front panel up, and flood the spacer with oil and let it soak overnight. If this is still not enough, the next degree is to do vacuum assist, if you have any kind of vacuum source available. It just has be rigged up to put suction on the temporary oil reservoir that you made with the spacer. If you can get decent vacuum on it for maybe a few seconds to a minute, some air from inside the pot should bubble up through the oil, and then pull some more oil in after the vacuum is released. This can be repeated a number of times. The pots are not truly "sealed," and will gradually leak everywhere, so any pressure difference is only temporary.

If you don't have any pot spacer hardware, you can do the same with a piece of rubber or plastic tubing, but it's trickier to attach. You want a tight fit, so the tubing is deformed and self-threaded onto the pot, to minimize oil and air leakage.

An alternative to vacuum is to put air pressure on instead, to force some oil into the pot. As you can imagine though, this could get quite messy - especially if you have a blowout in the tubing attachments.

Ed


Re: Another A5 board repair attemp - help needed

Rogerio O
 

Progress!
I had already replaced R2012 but forgot to check R2013, which was open!
Both have been replaced with TE RN73C2B10KBTDF from Mouser (10K, 0.1%, 10ppm).
Now the scope boots with TEST4 FAIL2 but after pressing A/B TRIG the horizontal lines is visible and the vertical position control work.
The next step is to find what is causing four dotted lines to appear near the top and bottom of the display.
I have uploaded a photo of the display to the album related to this thread (https://groups.io/g/TekScopes/album?id=256231).
Are they related to the error?
Thank you all for the help.
Roger


Re: 475M metal can caps

Michael W. Lynch
 

I have restored several of this family of scopes. Finding OEM style caps that are good is not a really viable option.

I use Modern radial lead caps and these adapters:

www.ebay.com/itm/Capacitor-Adapter-15-5mm-triangle-recapping-vintage-equipment-Tek-465-kit-x5/273254508468

I would say that you have issues with you -15 and -8V Supply. Caps may help rectify some of those issues. A Good place to start in any case. Get you supplies back in spec and you will go a long way to fixing the scope.

Good Luck!
--
Michael Lynch
Dardanelle, AR


Re: Clean and Lubricate Pots in Tek 475

 

You are describing the "A & B" (Allen Bradly) pots. I just got through going completely through my 475 after years of putting up with attenuator "leaf springs" not making good contact and the vertical and intensity pot problems you are seeing in you father's 475. I removed the vertical board preamp board and unsoldered these A&B pots from the PC board. I then removed the 4 screws and completely took these vertical position pots apart. I put a little Deoxid into them and tried to find the problem with the stiffness and the "springback" of these pots with little success. For some reason I could not locate why they turn ok when apart BUT are stiff when assembled. Fortunately I had picked up a "parts" 475 some years ago for fixing up my 475. The parts 475 had Bournes installed in this unit in all of the areas of vertical position, brightness, horizontal position, astigmatism, focus and so on. So I bit the bullet and did the work necessary to change the Bournes pots into my 475. This requires removing the necessary PC boards in some cases and is a pain in the ass. I see a seller on the bay that is selling the 311-1397-00 vertical pots that are brand new. I would suggest strongly that you buy these and save yourself a lot of grief in the long run. He also has the horizontal position pot and others for this scope. Now my 475 controls work just like they did from the factory and intended. I don't know why the A&B pots fail years later. The A&B pots seem to be used in the early units and then the Bournes in the later units. Maybe because A&B went out of business?
But after cleaning the gold contacts in the attenuators and generally cleaning up this area I am now very happy. Do the work and you will be happy with the results.
Bill


Re: Another A5 board repair attemp - help needed

Siggi
 

Hey Roger,

If your DAC's off, then all bets are off, and this could well be your sole
problem, so kudos on measuring the +1.36V and the -1.25V references.
The DAC's reference is a current, not a voltage, so it's practically
impossible to figure out what's up there by measuring voltages. You should
have very close to zero volts between pins 14 and 15 of the DAC though.
Likely you simply have a bad trace or a bad component in the DAC's
reference circuit, and the best way to check is by continuity and
resistance measurements. I think if you measure R2010/2011/2012/2013, and
how they connect up to pins 14 and 15, you'll find that there's either an
open resistor, or an open trace somewhere. The best way to do this is to
measure from the exposed contacts on the resistors and to the pins on the
IC.

You're on the right track - good luck,
Siggi

On Fri, Nov 6, 2020 at 12:03 PM Rogerio O <rodd414@gmail.com> wrote:

This time I got the error message test 4 fail2 (but still no trace), but I
guess it is not the main problem for the moment.
I tried to check the +1.36V and the -1.25V as suggested in other trend,
and they are VERY off.
The positive voltage is 0.258V (measured @ C2420) and the negative voltage
is -0.234V (measured @ R2421.
The +10V Ref to U2101 is ok.
I used a hot air gun to desolder the smd parts, including the DAC.
Is it possible that I have fried the chip?
I am checking the voltages around Q2320, U2420A/D and try to figure out
how this circuit works, since it is where these voltages are being
generated.







Re: Clean and Lubricate Pots in Tek 475

Eric
 

Jeff contact me off list and we can see what we can work out on the
calibration. But tek them selves is a calibration option as well I called
them about a 465 a while back and they quoted me $100.00 for a factory
calibration.

On Fri, Nov 6, 2020, 7:16 AM Jeff Dutky <jeff.dutky@gmail.com> wrote:

Ed Breya wrote:
First try lubing the pot shaft bushings from outside - remove the knobs,
and give them a generous drenching
with light oil, then rotate them lots of times
I tried this straight away, and it seems to have eliminated the
"spring-back" in the vertical position pots, but they're just as stiff as
ever. The intensity pot has some kind of "scratchiness" in it's first 30%
of rotation, and that hasn't been affected much at all by lubrication
either, but now it's clear to me that the trace is simply too dim to be
seen for the first 15-20% of the pot's rotation, so I'm not too concerned.

As you say I will let them sit overnight and see if things change.

The sources I've found on-line have the pots for very reasonable prices,
so I guess if worse comes to worst I can always replace them (no matter how
daunting it appears to be to get the boards out to unsolder them). If they
loosen up overnight, however, I'll take the win.

It's been quite therapeutic to be able to make even minor repairs to this
instrument, and to discover that it was not imminently going to destroy
itself because some part had worn out from age or disuse. Even if it's not
operating 100% perfectly it's still a wonderful scope, delightful to use,
and more than adequate for my purposes.






475M metal can caps

Bob Isselhard <robertisselhard@...>
 

I recently acquired a TEK 475M and purchased a hard-copy manual for it. I put the probe on channel A input and attached it to the calibrator. Then I moved the probe plug to channel B input. The amount of signal is correct (square wave, 300 MV) on either channel. I can not stabilize the trace however. It continues to slide to the left no matter where I move the TRIGGER SOURCE controls. I have only one probe so I can't exactly try the "connect both probes to the CALIBRATOR routine.

I checked the power supply voltages as per the manual and found the following:

+50 volts = +49.7 volts
+110 volts = +110.4 volts
+15 volts = +14.96 volts
+5.0 volts = +4.94 volts
-15 volts = -21.93 volts
-8 volts = -5.3 volts
UNREGULATED +50.volts = +64.3 volts

I looked at the large can caps and removed C1472, the filter cap across the diode bridge for the -15.0 volt supply. It actually looks good (3700 MFD, .47 ohms ESR).

Now the problem comes in. I have never worked with these before and did not realize there was an additional lug on the cap that was soldered to the lead that comes out on the other side of the board and is connected to the -15 volt test point.

I would like to obtain an exact replacement physical configuration-wise and re-solder the can lug to the test point and have it held down to the circuit board that way. However, if I can't find one, I can obtain a radial-lead, wired-in electrolytic and bridge the necessary connections. I wonder what to use to secure it to the metal piece adjacent to it? Hot glue? Super glue? Seal all? (one tube epoxy). I wonder what others have done here when replacing these large can caps? Granted, this one appears good, but why re-insert an old cap when I can replace it with a new one?

Any ideas gratefully accepted.

73, Bob K5INW


Re: Making TDS 5xx/6xx elastomer buttons

Stephen Hanselman
 

Derek,

First where are you and then if it’s the US which elastomer do you need. I have a number of ‘pulls’ that are available for $10+shipping.

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Nov 5, 2020, at 11:22, Derek Chauran <af7ux@outlook.com> wrote:

Hello - I have a TDS 510A and a 640A, with only one set of buttons between them. I looked into buying set, but they are around $100 shipped, which is hardly worth the expense.

So I decided to use this as an opportunity to work on my CAD skills, and designed a set of buttons, and a mold for them. The plan was to 3d print the mold, and use RTV to cast the buttons with copper tape placed in the mold for the contact surfaces. This plan seems to be viable, except that my printer is having some issues and I cannot get it to print correctly right now. Is there anyone else who would be interested in collaborating on this effort? There's no money in it, and I plan to "open source" the files once I have finished.

Thanks,
Derek





Re: Another A5 board repair attemp - help needed

Rogerio O
 

This time I got the error message test 4 fail2 (but still no trace), but I guess it is not the main problem for the moment.
I tried to check the +1.36V and the -1.25V as suggested in other trend, and they are VERY off.
The positive voltage is 0.258V (measured @ C2420) and the negative voltage is -0.234V (measured @ R2421.
The +10V Ref to U2101 is ok.
I used a hot air gun to desolder the smd parts, including the DAC.
Is it possible that I have fried the chip?
I am checking the voltages around Q2320, U2420A/D and try to figure out how this circuit works, since it is where these voltages are being generated.


Re: Read Out problem 2710 SA

Graham <grumss@...>
 

Hi all,
Yes very old post but i thought i would add my findings to hopefully be helpful to others..

My screen also has gone into the dreaded displaying garbage symptoms. After spending a lot of frustrating time playing around i think i can put my finger on the problem (mine anyway), digital is certainly not one of my strong points but here goes..

It seems the SA's display pages are changed by pin 7 of U260 (PLS159), this chip is supposed to send a negative pulse to a binary counter (U326). The binary counter counts until the correct page/s is displayed then is suppose to stop.
The binary counter also sends signals to other chips including U308 which controls blanking and "dotenable"! (one of the classic things we all see with the fault)...
What seems to be happening (in mine anyway) is that U260's pin 7 is caught in a near mid state, around 4V in mine- any noise in the circuit is +- on the 4v and sending the page select counter into near constant counting- this seems to be why we see all of these unusual displays....

Now to prove the point, i pulled the pin 7 output up to 5v with a high value resistor- the SA now always boots to a spectrum display which i assume must be default with the initial (000?) binary output from the counter.. no other screen data is displayed but at least i can see a working spectrum..
I experimented with mosfet switching on pin7 to lighten its load but had no success.. I dont think it pulls down at all...

Now all i have to do is find a PLS159, the code and try to program it! GEEZ!! (id very very thankful if one of you guys can help)
I dont think the PLS is doing very much looking at its clock, but for me the code would be very difficult to invent..

Hope i have been of help.
cheers, Graham VK3XDK (grumss@yahoo.com.au)


Re: SPC fails on TDS7404

Charly Marina
 

Hi stan i would look in your inputs.. if one of the input is not good/out of spec.. you can get an spc fail also.


FS: 7633 CRTs qty 3, PC boards from 7633 - all except HT

 

I have the CRTs and PCBs from three scrapped 7633s (EHT failed).

In Kenilworth UK

Can ship if needed, but prefer collection for the CRTs.

All good AFAIK.

Offers ...

David


Re: For sale 6dj8’s

 

Take some or all

On Nov 6, 2020, at 7:47 AM, n9llo via groups.io <N9LLO=aol.com@groups.io> wrote:

Probably never use them so...
6DJ8’s
New in box
14 national brand
1 RCA
10 bux each plus shipping usps priority mail.

Chris
W9RP
n9llo@aol.com





Re: Another A5 board repair attemp - help needed

Siggi
 

On Fri, Nov 6, 2020 at 6:43 AM Rogerio O <rodd414@gmail.com> wrote:

Thank you for all the replies.
You were right, the beam finder button was stuck and I was unfamiliar with
this image.
Sorry for wasting your time on this trivial issue.
Don't sweat it - we've all been there. I spent hours trying to suss my
2467, where the beam finder was simply stuck :).


But I have fixed this and I can see that the scope has problems.
There is no horizontal trace, just a series of dots and a message on the
top left corner of the screen saying A1 voltage and some number.
Intensity and position controls does not have any effect on the display.
Vertical gain has also no effect.
Focus and Horizontal time/div are working.
I have uploaded a photo of this display (
https://groups.io/g/TekScopes/album?id=256231)
Any hints on how to proceed with the troubleshooting?
Everything you're seeing could be explained by the intensity control being
at zero, whether due to the pot itself, or due to a fault on the A5 board.
If the intensity is set way down, you wouldn't see a sweep.
A fairly direct way to diagnose this would be to measure the DIR signal on
the A5 board, see where it's at, and whether it responds to the intensity
pot.

Also, as Leo (satbeginner) says, set the scope up for where it's definitely
sweeping:
CH1/2 coupling at GND.
Trigger in AUTO LVL.
Reasonable sweep speed (100us/div, perhaps).

The TRIG'D light is also a handy diagnostic aid. If you input a signal to
the scope and get it to trigger on it, that indicator will light up whether
or not you see the sweep.
So, hook a probe up to CH1 and attach it to the calibrator, then set AUTO
LVL triggering for CH1 and see whether your TRIG'D indicator lights up. If
so, you almost certainly have a sweep, you just don't see it.


For sale 6dj8’s

 

Probably never use them so...
6DJ8’s
New in box
14 national brand
1 RCA
10 bux each plus shipping usps priority mail.

Chris
W9RP
n9llo@aol.com


Re: Clean and Lubricate Pots in Tek 475

 

Ed Breya wrote:
First try lubing the pot shaft bushings from outside - remove the knobs, and give them a generous drenching
with light oil, then rotate them lots of times
I tried this straight away, and it seems to have eliminated the "spring-back" in the vertical position pots, but they're just as stiff as ever. The intensity pot has some kind of "scratchiness" in it's first 30% of rotation, and that hasn't been affected much at all by lubrication either, but now it's clear to me that the trace is simply too dim to be seen for the first 15-20% of the pot's rotation, so I'm not too concerned.

As you say I will let them sit overnight and see if things change.

The sources I've found on-line have the pots for very reasonable prices, so I guess if worse comes to worst I can always replace them (no matter how daunting it appears to be to get the boards out to unsolder them). If they loosen up overnight, however, I'll take the win.

It's been quite therapeutic to be able to make even minor repairs to this instrument, and to discover that it was not imminently going to destroy itself because some part had worn out from age or disuse. Even if it's not operating 100% perfectly it's still a wonderful scope, delightful to use, and more than adequate for my purposes.


Re: Troubleshooting an old Tek 475

 

On Fri, Nov 6, 2020 at 04:57 AM, Jeff Dutky wrote:


I probably need to adjust the horizontal timebase, since I replaced a
capacitor on the sweep generator board, and because I have suspected that the
timebase may have drifted all along (of course, maybe that was due to the bad
capacitor, so that might have been fixed), but I don't have any of the
equipment needed to do a real calibration, and the timebase isn't off by
enough to make gross adjustments worthwhile.
My memory urges me to write the following:
If you replaced one of the physically larger timing capacitors (metal cylinders, the smallest about 2cm length), be aware that these are matched sets (I think 3 pcs, marked by a single letter, like "J", "K" or the like, the same for each set). At calibration time, you can't adjust their timings individually.

Raymond


Re: Clean and Lubricate Pots in Tek 475

 

tenareze32 wrote:
It seems a nice idea to restore it to its original factory state, but unless you plan to use it in your job it is probably not worth it.
Absolutely true. This is just for a hobby, and for nostalgia (it belonged to my late father). Even for the hobby work I don't think I need it fully calibrated, as long as it's not wildly wrong it should be fine for my needs, but if I could get it properly calibrated for under $300 then I would consider it.


Re: Another A5 board repair attemp - help needed

satbeginner
 

Make sure the triggering is set for auto, even select line trigger just to force the scope to trigger.

Check for the trigger light being on.
Select one channel, eg 1, and try to adjust vertical position.

Let us know what you see.
Pictures are a great help.

Succes,

Leo

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