Date   

Re: Troubleshooting an old Tek 475

Göran Krusell
 

Hi, the R1059 and C1059 low pass filter is filtering the +110V voltage, the values are not critical.
Göran


Re: Clean and Lubricate Pots in Tek 475

 

You should be aware that the WD-40 of 50 years ago is not the same stuff you get these days - I believe for example that it used to contain "duck oil" and that the formulation has changed at least twice since then.

Personally I wouldn't let it near a potentiometer.

David


Re: Clean and Lubricate Pots in Tek 475

 

Eric and Greg,

The recommendation for WD-40 comes directly from the 475 Oscilloscope Service Manual, page 4-2 under Maintenance, Cleaning, Switch Contacts, the exact passage reads "There are three recommended switch lubricants. They are Silicone Versilube (General Electric Co.), Rykon R (Standard Oil), and WD-40 (Rocket Chemical Co.)." So, while Tektronix DOES specifically recommend WD-40, it is not recommended for this use. The manual specifically says of the potentiometers in the unit "most of the potentiometers used in the 475 are permanently sealed and generally do not require periodic lubrication." Of course the period that they were considering was presumably much shorter than 50 years.

I've ordered a set of syringes and industrial needles to try either forcing some lubricant down the shaft, or into a the partially opened back end of the modular pots. I would like to order some DeoxIT to use in place of WD-40, but the range of options, and CAIG's claims for the product, give me pause.

I'm not too worried about using WD-40 on the unit in general, and I'm not terribly concerned with preserving these specific three pots, as there appear to be readily available replacement units at reasonable prices (I am going to order a full set of replacements for these three pots under any circumstance. The channel #1 vertical position pot can be easily replaced without even removing the vertical input board from the unit, and that is the one that is giving me the most trouble. The channel #2 vertical position pot is not as troublesome, and I don't use the beam intensity adjustment, which is the one with most serious problems, nearly as often as I do the vertical position adjustments).


Re: Troubleshooting an old Tek 475

 

Okay, I'm not nearly qualified to understand what C1059 was doing in the sweep generation circuit, I mean I can trace out what it's connected to, but my EE fluency ends with "which way to Kirchoff Cafe" and "My hovercraft is full of eels." The failed part still appears to act like a capacitor (in the 200nF range), at least from what my multimeter can tell (I don't have an ECR meter or a working comparator bridge to check it any real way). Whatever the case, it was clearly the culprit in disabling the horizontal sweep. I suppose it also may have been distorting the timebase, but even before this failure the timebase wasn't off by more than a few percent (if that, as I was judging the timebase by comparison to the built-in calibrator signal, which appears to be off by 5% or more), and if C1059 played any significant part in the timebase itself then I would expect a change of an order of magnitude in C1059's value to have more than a 1% effect on the timebase.

As it is, I checked the value of the replacement capacitor to make sure that it was within 10% of the specified value. I even ordered several replacement parts so I could select the one that was closest to 3.6uF, and both the candidates were right about 3.5uF, so I feel pretty good about the transplant not screwing up the host circuit.


Re: Clean and Lubricate Pots in Tek 475

Greg Muir
 

Eric,

I am aware that there are various camps regarding the use/not use of WD40 as a cleaner & lubricant for potentiometers. I myself shy away from it given past experiences with the behavior of this penetrant/lubricant and it’s properties over time.

There has been much said about the combination of the carrier and lubricant used in this product and its propensity to leave behind residue after the carrier evaporates. In my experience I have witness a very heavy and sticky form of oil that forms after extended periods of time.

Aside from that I adhere to products listed as being specifically formulated for electronic purposes. In many respects it is better to be safe than sorry especially if the target item is non-replaceable as those things used in legacy equipment. Granted Tek did specify (or recommend) WD40 in a couple of their documents but it was not widespread. This was possibly due to a recommendation made by one or a few individuals. Although I do not know where these recommendations were made I feel that the factory designed service lifetime has past some considerable time ago.

I am sure that if the WD40 company felt safe with recommending its use on potentiometers they would have included that in their promotional literature. But when they state that it is useful on “larger electric motors, armatures, relays, electric panels, and generators” I feel a little unsure about committing it to sensitive electronic purposes other than those that are stated.

There are plenty of good products out there on the market targeted at applications like that in this discussion. Why not use them?

Greg


Eric wrote:

“Greg I have to disagree with you on this one…..”


Re: 475M metal can caps

greenboxmaven
 

One thing Tektronix did a great deal was to only have one voltage supply with a zener reference, it's output was the reference for other voltage supplies. Sometimes there would be a cascade of supplies giving reference to others. Needless to say, if any one of them is not accurate and clean, the following ones won't be either. The absolute worst examples I ever dealt with were some Yamaha stereo receivers where one zener ultimately controlled cascaded power supplies producing nine different voltages.

Bruce Gentry, KA2IVY

On 11/6/20 5:27 PM, Paul Amaranth wrote:
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


Re: 475M metal can caps

Bill Perkins <sales@...>
 

Here's some work I did 20 years ago on a Tek 570 S/N 215:

https://www.pearl-hifi.com/07_Facility_Tour/Tek_570_215/Internal.jpg

I made the parts from FR-4 and used stake-in solder terminals from Keystone.

Bill

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


Re: Troubleshooting an old Tek 475

 

Raymond wrote:
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.
The cap that I replaced is labeled C1059 and is the smallest capacitor on the Timing Circuit Board. In the parts list it is indicated simply as "3.6 uF, Elect., 125 V, 10%" so I don't think it's part of the matched set. There are two sets of capacitors on that same board (C1071,72,73 and C1082,83,85 that are specifically marked in the parts list as matched capacitors of 10uF/0.1uF/0.001uF) but this is not one of them.

Thank you for the warning, though; it is well taken.


Re: Clean and Lubricate Pots in Tek 475

 

Here is the link that says that removing the vertical amplifier board is not as involved as you would expect it to be (though I'm not sure I understand exactly what he is saying is involved in removing the attenuator switch assembly): https://entertaininghacks.wordpress.com/2018/02/27/renovating-a-tektronix-475-timebase-switches-potentiometers-and-hf-response/

This also covers most of the problems I've been seeing. It's an excellent post.


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





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