Date   

Re: 475M metal can caps

Bob Isselhard
 

Thanks Paul, Michael and Leon.   I told Michael in a PM I ordered five of the spacers off Ebay immediately after following his link.  Yeah, I know, power supply problems can doom the best of efforts.  That’s why I ordered the hard copy manual as soon as I saw the problem with the trigger. I wanted to see exactly where all the test points were and exactly what they should read.  I don’t have a second scope to check ripple  but getting the voltages correct on the -15 and -8 volt rails may solve this.  If not, I’ll no longer be a TEKSCOPE beginner, but a “veteran” with solder splashes and flux odor to boot.  When I pulled the -15 volt electrolytic, I checked it and it shows 3700 uf and .47 ESR.  But I’m not about to put a 10 + year old cap back in.

Thanks to all for the assistance so far.

Bob

Sent from Mail ( https://go.microsoft.com/fwlink/?LinkId=550986 ) for Windows 10


Re: Clean and Lubricate Pots in Tek 475

 

Bill,

I had a closer look at the vertical input board and it looks like it might come out with less work than I thought. I haven't verified this, but it looks like the BNC connectors might not be mounted to the front panel (I thought I read a blog entry about repairing a 475 that said something about this, but I can't it now, however this post of EEVBlog shows a full teardown, which seem to support my hypothesis <https://www.eevblog.com/forum/projects/tektronix-465-repair-and-restoration/>). If that's true, then getting at the two vertical position pots is much easier (if not quite trivial). I also noticed that the only pots that got stiff are the "double stack" ones. The single stack, which appear to be from the same manufacturer, are all easy to turn.

It looks like I can buy replacements for between $10-$20 per pot, which I think is a fine price. If I can get the vertical input and main boards out without too much fuss, and if just lubricating them doesn't help, then I will just replace them.

I'm not sure who made these pots, but all of them (with the possible exception of the two trigger level pots, which are metal cans rather than plastic blocks) are brown/black plastic with dark red inserts. The replacements I've found online (from talonelectronic.com and rshopboss.com) are blue, and my scope was assembled in late 1974, so I'm assuming that it has A&B pots.

I have been very happy with the results I've gotten so far with what I consider fairly minimal effort: I only had to break out the soldering iron ONCE on this old thing, and that was completely unavoidable; to replace a obviously very dead electrolytic capacitor on the sweep board.


Re: 475M metal can caps

Leon Robinson
 

Or herd cats.  Electronic equipment is like a house, the power supply is the foundation, 
If it,s not right nothing else is.


Leon Robinson  K5JLR

-------- Original message --------
From: "Michael W. Lynch via groups.io" <mlynch003=yahoo.com@groups.io>
Date: 11/06/2020 4:41 PM (GMT-06:00)
To: TekScopes@groups.io
Subject: Re: [TekScopes] 475M metal can caps

Trying to "fix" a TEK scope that has faulty power supplies is almost like trying to push a rope.

--
Michael Lynch
Dardanelle, AR


Re: 475M metal can caps

Michael W. Lynch
 

Trying to "fix" a TEK scope that has faulty power supplies is almost like trying to push a rope.

--
Michael Lynch
Dardanelle, AR


Re: Clean and Lubricate Pots in Tek 475

 

Ed:
The A&B pots were designed to be modular. What I mean by this is that they are designed to fit together such that you can make a 1,2,3 section, or probably more, multiple pots out of the sections. The 311-1397-00 is one example of what Tektronix did with these. So you start with a front module that has the shaft and is the "thread" end of the assembly. Then you just add the first variable resistor section which fits into the front shaft section and mates with the "driver" on the rear of the shaft section which is also "keyed" so that you cannot assemble these incorrectly. Then the second variable resistor section is designed to "mate" with the first variable resistor section with a little driver piece to provide the link between the first resistor and second resistor shaft. There are no "rubber" gaskets between the resistor sections in this design. Then this can continue until you have the number of sections you need. A&B obviously made resistor sections in different resistance values so you could make up a control with say 5K in the first and 10k in the second and so on. I have no idea exactly what values A&B made available. Then there is a back plate where the 4 screws go through to the front shaft section in the front and hold the whole assembly together.
I found that each resistor sections would turn very easy and the front shaft was turning easily also, but when the whole assembly was put together it was stiff and springy. I tried to find the source of the stiffness with no success whatsoever. I left the screws loose and still no relief. The back section shaft was not touching the rear plate so no problem there. You cannot disassemble the individual sections but it is easy to get the Deoxid into them and that got rid of the "scratchiness". These controls were not stiff and springy at the beginning when I got the 475 in 1980 or so but something inside of each resistor section must somehow add up to the whole problem. I also tried to clean each section in IPA and then reassemble but to no avail. I then tried to "lubricate" the section shafts with the same results. I guess what I could do is destroy one section by "tearing" it apart by force and see what is inside of the section shafts to see what A&B put inside. These are the black pots.
The newer Bournes pots are riveted together and must be factory ordered as to the resistance values you need for each section. These are the blue pots. A little research told me that Bournes bought A&B sometime in the past. The shafts of the A&Bs were not bent in any way and were connected to the front panel of the 475 with the usual fiber shafts that Tek liked to use when the pots were mounted on the PC boards way back in the instruments. The Bournes are an exact replacement in the PC board after removal of the older A&B pots, as you would expect.
There is NO way to remove the vertical position pots in the 475 vertical preamp board without removing the board from the instrument. Then it is easy to unsolder them from the PC board and work on them.
Bill


Re: 475M metal can caps

Paul Amaranth
 

I will second Michael's recommendation. The little adapter boards make
for a very neat and professional looking repair. In a pinch I've used
PNP blue to etch my own, but it's easier to buy them ready made.

Use 105C caps if you can.

On these scopes if the power supplies are not right, nothing works right.
Always ensure the power supplies are correct before looking at anything
else.

Paul

On Fri, Nov 06, 2020 at 10:15:53AM -0800, Michael W. Lynch via groups.io wrote:
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
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows


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

Ke-Fong Lin
 

Hi,

I can be interested, do you have the part numbers of the available PCBs?
I have a 7623 to repair/upgrade. But almost all PCBs between 7623 and 7633 are common.
In fact, it seems 76xx series scopes share a lot in common.

Best regards,


Re: Clean and Lubricate Pots in Tek 475

Eric
 

Greg i have to disagree with you on this one. Tektronix them selves used to
have a product called "no noise" this was actually replaced with wd40. A
can of wd40 actually has a tektronix part number. The tektronox part number
is 006-2574-00.

Eric


On Fri, Nov 6, 2020, 3:25 PM Ed Breya via groups.io <edbreya=
yahoo.com@groups.io> wrote:

On Fri, Nov 6, 2020 at 10:05 AM, Bill wrote:


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.
It depends on the particular construction, which may vary a lot between
brands. styles, and grades. If you refurbish a pot and it still binds after
thorough cleaning and lubing, look at all the possible parts that can
deform with age and use. First, make sure the shaft isn't bent, which is
especially possible on 1/8" and smaller ones. Next, check the axial end
play. It should be able to move in and out at least a few .001" at any
rotational position. If not, then the whole thing is just too tight, likely
due to any rubber and plastic parts deteriorating or cold-flowing.

The definition and construction of a "sealed" pot varies. Fancier, better
grade ones may be more elaborate and include rubber gaskets between parts,
and a rubber shaft seal like an o-ring at the bulkhead, or on a neck cut in
the shaft. This is what tends to give the "springback" feel, due to
deterioration and swelling of the material. If you can find a fresh o-ring
equivalent to the original, replacing it should fix that problem. An
alternative is to just delete the o-ring - the benefit of the seal isn't
that big a deal anymore, in a benign hobby/lab environment. If the o-ring
is at the bulkhead, eliminating it will likely also increase the axial
play, possibly too much. You can try a thinner o-ring or add appropriate
shim washers to tweak it.

If there are no shaft seals, then look at any rubber gasket layers - the
rubber gets thinner over time under compression, so the whole assembly gets
shorter, reducing axial clearance inside. If there is a shim washer at the
bulkhead, you can try a thinner one or deleting it, but be aware the shim
is also part of the thrust bearing function, so the pot may run rougher
without it. If you can't effectively shorten the rotor assembly, then you
can lengthen the body by say making new gaskets with thicker or fresh
material, or adding shim washers between sections, around the screws.
Again, high grade environmental sealing is not that important anymore.

If there are no rubber parts at all to blame, then cold-flowing of the
plastic body parts is the likely cause. Study the construction and look at
all the options to either shorten the insides, or lengthen the outsides.

Ed






Re: Clean and Lubricate Pots in Tek 475

Ed Breya
 

On Fri, Nov 6, 2020 at 10:05 AM, Bill wrote:


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.
It depends on the particular construction, which may vary a lot between brands. styles, and grades. If you refurbish a pot and it still binds after thorough cleaning and lubing, look at all the possible parts that can deform with age and use. First, make sure the shaft isn't bent, which is especially possible on 1/8" and smaller ones. Next, check the axial end play. It should be able to move in and out at least a few .001" at any rotational position. If not, then the whole thing is just too tight, likely due to any rubber and plastic parts deteriorating or cold-flowing.

The definition and construction of a "sealed" pot varies. Fancier, better grade ones may be more elaborate and include rubber gaskets between parts, and a rubber shaft seal like an o-ring at the bulkhead, or on a neck cut in the shaft. This is what tends to give the "springback" feel, due to deterioration and swelling of the material. If you can find a fresh o-ring equivalent to the original, replacing it should fix that problem. An alternative is to just delete the o-ring - the benefit of the seal isn't that big a deal anymore, in a benign hobby/lab environment. If the o-ring is at the bulkhead, eliminating it will likely also increase the axial play, possibly too much. You can try a thinner o-ring or add appropriate shim washers to tweak it.

If there are no shaft seals, then look at any rubber gasket layers - the rubber gets thinner over time under compression, so the whole assembly gets shorter, reducing axial clearance inside. If there is a shim washer at the bulkhead, you can try a thinner one or deleting it, but be aware the shim is also part of the thrust bearing function, so the pot may run rougher without it. If you can't effectively shorten the rotor assembly, then you can lengthen the body by say making new gaskets with thicker or fresh material, or adding shim washers between sections, around the screws. Again, high grade environmental sealing is not that important anymore.

If there are no rubber parts at all to blame, then cold-flowing of the plastic body parts is the likely cause. Study the construction and look at all the options to either shorten the insides, or lengthen the outsides.

Ed


Re: Clean and Lubricate Pots in Tek 475

Greg Muir
 

Be careful using oil on a potentiometer. I have seen some pots where oil has loosened the binder holding the carbon to its surface and ruined it. In addition oil works wonderfully to capture contamination causing future problems.

This is why control cleaners are manufactured specifically for cleaning & lubricating pots & switches. The lubricants contained in these products are formulated not to cause additional problems. WD40 and solvents of an aggressive nature are not made for electronic applications such as this.

Greg


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
 

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.

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