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Hi group,

My old 576 works mostly fine after fixing a very surprising fault, but needs some more light repair.
- Knobs
- Push-button switches

This unit comes originally from Hewlett Packard's H.P.A. Division, I assume the High Power Amplifier Division, and is clean and in fairly good shape after all these years. Serial no is B283900 and tested by V. Fredrickson ?
There is also a sticker from hp-MSD-R&D, and HPSJS Asset, all with inventory numbers, so this Tektronix Curve Tracer has been in several good hands at the competitors premises.
Even the readout is working fine.

However, even the sun has spots, two of the knobs are falling apart. Looking in the manual it is;
pos 85; 366-1095-00, knob, gray - Peak Power Watts.
Q) This knob (the outer knob) can maybe be glued. Question is what glue you recommend.
The gray plastic is brittle after all years and the inner aluminum part is loose, but not enough that I can take it out.
pos 103; 366-1007-00, knob, gray - Variable Collector Supply
Same thing with this knob, the inner part is loose and the outer plastic is broken.
Q) Any hint where I may be able to find the original knob is welcome.
In the mean time I will use an other larger knob with 1/4" hole.

The push button switches are more tricky.
They have oxidized internally and gives poor intermittent contact.
The vertical PCB with Display Invert, Zero and Cal buttons was fairly easy to remove.
Disassembling the push switches and cleaning the contacts.
The three horizontal rows below with theirs PCB's was much more difficult.
Q) The easy fix is to spray from the back (with what spray? WD-40 maybe?), but to remove them to do it more thorough is a challenge.

Has anyone done this?
There is no space to remove the boards backwards as there is a think cable bundle in the way.
As I understand, the whole front panel must be moved forward so the buttons can be pushed in and then taken out.
Q) How to do this best is my next question. I've tried, but not hard enough.
Remove the CRT ... ?
Something hidden is holding the front panel back despite having removed or loosen all possible visible screws found.

The very first surprising fault was an individual contact in the rotating cam-shaft in Step Generator Amplitude.
The 20mA step was always active independent of my settings, so no way to reduce the step amplitude lower than 20mA.
Under the microscope, it looked as it came like this from the factory ??
Luckily my first DUT was a TO-3 2N6510 power transistor, so it survived.
Easy fix, just to re-solder this contact to the PCB in its intended position.

Bo

Dear Bo, BRAVO to have found this classic 1980 machine.

Suggest you get the printed service manual for the serial number range and follow the mechanical disassemble proceedure

For swith contacts NEVER USE WD40, dangerous to plastic parts ans WILL NOT clean a contract.

WD40 is a petroulum distillate TO REMOVE WATER, not a cleaner or lube.

USE ONLY isopropyl alcohol and ELECTRONICS GRADE CONTROL CLEANER / LUBE !!!

Some are afficanados of Deoxit, but we never use it.

For the knobs, very typical, deteriorated plastic, breaks at the set screws.

Impossible to glue to gather after they break.

Suggest you post the photos and TEK part numbers of all the broken knobs here, in BUY..SELL..WANT and other Tektronix fouums also EEVBLOG in Wanted.

Finally contact to Tektronix Vintage Museum in USA, Beaverton Oregon who MAY have these very rare knobs.

Bon chance

Jon

I WISH that someone would start making replacement knobs for the
Tektronix Curve Tracers. These are still HIGHLY desirable machines but
almost all of them have some broken knobs and there simply aren't enough
salvaged knobs to fix all of the machines out there.

Not sure which pushbutton switches you are referring to, but none of them require removal of the CRT to remove.

The 3 rows of step generator switches near the bottom right side of the instrument can be 'easily' removed from the instrument. I've done it myself as I had similar problems when I got mine and restored it. You need to remove the 'Amplitude' switch assembly board. The 'Vertical', 'Horizontal', 'Display Offset' and 'Amplitude' switch assembly PCBs are all attached to a metal subframe via two screws in the back. If you remove these screws and and the knob from the front, you can easily remove these switching assemblies. You might also need to remove those big tan resistors to remove the Vertical and Horizontal switching assemblies. But once you get those out, you will have much better access to the 'Display Switching' PCB which has the 'Zero', 'Cal', and 'Invert' buttons.

With the 'Amplitude' switch assembly removed, you can then get better access to the 'Step Gen Offset', 'Step Gen Pulse' and 'Step Gen Rate' PCBs with the push button switches on them. There are 4 long screws that hold the switch PCBs to the chassis. These can be accessed for removal by removing the Standard Test Fixture. It is still a very tight spot, but it is doable. The most crucial part (in my opinion) is removing the plastic pushbutton switch actuators without breaking them. I used a pair of pliers and very gently pulled them off, but I still managed to crack a couple of them. Maybe someone else in this group has a better method for removing them.

I wouldn't recommend using WD40 to clean the switches. WD40 (at least the standard formula) is not an electronics cleaner. I did use Deoxit D5 and F5 to clean these switches, but as you can see, some of the more experienced members here advise against using this.

more notes....

1/ Exercise all buttons and switches periodically.

2/ Can use control spear from front no need to open

3/ Keep watch on INTEN to avoid burn in of CRT, and keep SCALE ILLUM, SCLAE FACTOR dimmed to prolong lamp life

4/ knobs upper INTEN FOCUS are VERY easy to break the plastic has deteriorated and they are very small,

5/ Bat switch to select test fixt at front porch , left/off/right VERY easy to bend or break, rare SwitchCraft leaf switch.

6/ Test fix HV protect house is easy to break and a pain to use.

Remove and either defeat the interlock switch OR replace wit a small Alco toggle.

Will post pix



Enjoy,

Jon

PS: All new repros are 3D filamnt and very waek plastic, no way to replicate knobs especally the complex ones.

Photos and markup here

/g/TekScopes/album?id=292639

576 Accessories to watch for:

Transistor and diode adapters from TEK or DIY,

176 high current pulsed test fixture (mercury wetter sealed relays and pulse line)

See photos

Jon

On Tue, Jan 30, 2024 at 06:14:48AM -0800, Jean-Paul wrote:

5/ Bat switch to select test fixt at front porch , left/off/right VERY easy to bend or break, rare SwitchCraft leaf switch.

Very easy to break and a very common problem. I had this issue with my
576 when I bought it. I did some research and posted the definitive
procedure to fix it.

/g/TekScopes/topic/74056702#167222

You can't find the original switch, but repair is not terribly difficult
(although a fiddly job) and donor switches are easy to find on ebay. When
I did my repair around the time of that post they were around $11.

It still sticks out though; it may be worthwhile to put a safety guard
on the toggle to save it from being broken off.

Paul
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows

I have a few videos on YouTube about restoration and alignments. Links are
below

Tektronix 576 Calibration -
Tektronix 576 First Impressions and Repair -


One quick question, Do you have the black or brown HV transformer?

Zen

Thanks all for all valuable hints and suggestions!
Very much appreciated!
However, this will take me some time to digest.

For the last quick question, I had to remove the sheet protection and look. My HV transformer is black. Looks fine.

So far I have been busy removing the front panel and during that, managed to destroy a plastic insulator on the shaft for the looping compensation control. Terrible to access without removing the front panel and the worst part to work on.

One issue I see is the combination of hard HSS lock screws and soft alumina shafts without some dedicated place for deformation. I intend to use a file to create a flat "dent" for the screw (if the screw is long enough) so the knob will more easily get off. Now the know was stuck even with the lock screw removed. Each time the knob is fastened there will be more screw marks in the shaft and one day it's stuck to it.

Until I find the correct part, I plan to use a piece of 9 mm plastic tube to place over the joint and replace the screws with longer types so it can be rotated securely. The variable capacitor shaft is 1/4" and the knob shaft is maybe 1/8".
Q) Should the capacitor shaft-bearing be "greased" for easy operation and if so with what?

Yes, exercising all controls is a good hint. It's like those analog radios making a terrible noise when you turn them on after a long period of inactivity (returning to the summer cottage after the winter period).

Q) I have one more question about what glue to use for the push switches buttons. Two has come of so far. I assume a soft glue not affecting the plastics is preferred? When you push one button, the other comes out rapidly with a snap and it may become loose one day.

Bo

Forgot to say;
I should of course change the tricky to access destroyed looping compensation part with some other easy to access.

Bon, very fine, glad for the progress..sorry for the issues.....

1. buttons....please, NO GLUE! nylon, etc, press fit. Popping due to binding, and dirty.

Use isopropyl alcohol to clean button sides, then apply control cleaner, lube from front.

We use a cotton tip with mineral oil to very sparingly lube the buttons
Buttons should move freely and not pop off

2. Looping Comp......
Now you learn that fiddling with ANY old equipment is risky, things easily break, plastic parts deteriorated

The Looping comp is very seldom used, only on very low ma/ div vert scale and odd test fixtures

99% time makes no difference, we set looping once and forget.
So it's not even needed to fix it. But Tektronix Vintage museum may have knobs and spares.

3. Did you See the 576 album photos I posted yesterday ( see link) on the group photo albums

4. What test fixtures and adapters do you have?

What kind of devices do you need to test?

Amicalement


Jon

There is a seller on eBay right now selling a lot of parts and pieces from 576 "pulls" (part harvesting). I have no affiliation, but they might be a good source of knobs and such.

I am in the middle of replacing all of the carbon comp resistors in my 576. All have drifted high. I have my 576 completely apart and I am planning on posting some pictures of the less accessible places on the 576 as well as some locations of resistors and capacitors that are not shown in the manual.

I have also come up with a prototype replacement for all the relays on the Display Amp board. No more issues from those sporadic rocker arm finger tab relays!

Dave

On Wed, Jan 31, 2024 at 09:25:11AM -0800, dc_rawding wrote:

I have also come up with a prototype replacement for all the relays on the Display Amp board. No more issues from those sporadic rocker arm finger tab relays!

Dave

Be sure to post info about that when you've proved it out. I would be very
interested in reading about that.

Paul

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix/Linux - We don't do windows

Bo we avoid the button snap/pop by pressing several gently, to hold the top of the depressed button and pervent the fast return that pops off the cap.

Easier to do than to describe.

Jon

Payback time. Everyone likes images, right?
Now uploaded and by mistake they ended up in Jean-Paul's previously uploaded images, so the same link as above.
/g/TekScopes/album?id=292639

I'm sorry for that Jean-Paul, newbie-mistake.
I've tried to make them "small" without loosing detail. Poor sharpness is the cameras fault, it cannot compensate for the button pressers shaky hands.

I owe you many replies, so this will be a small novel. There is a possibility to mute this thread for others less interested.

This time:
Old buttons in Greece, most sold out though.
Good pictures!


Close match of the Variable Collector Voltage knob:


The shaft isolated joint:

complete coupler:


Good you warned me about WD40.
The push-button with images uploaded was the first I attempted to fix, not yet tested.
I started with the small moving contacts in silver "cleaner" for a short while. The kind of liquid my wife use and that rapidly does magic to other parts of silver, like forks and knives et.c.
I then rinsed them thoroughly and carefully in water (beware not to loose them under ground in some pipe).
Used a cotton-stick to "clean" the inside (not easy at all) and then assembled it all.
Luckily there was space enough to remove the actuators backwards, so no need to de-solder anything.
As the last step I gave it a short dust of WD40, something I shouldn't have done.

Today I bought the real stuff, isopropyl alcohol. Seems to have many names.
and then re-cleaned the same switch board (see images). No damages to the plastics what I could see, but maybe slightly sticky. One extra thing I also did was to use the unused connectors in order to improve contact. Image #19.

Q) One minor question remain, should the tiny lock-pin be greased or not? Image #20.
I guess it was. Then what to use?

One of the pictures, #22, show a black inner pin. This pin is not used, so I did not bother.

More to follow.

Hello Bo, just make sure you don't have to go through the learning curve with cleaning old plastics. I paid the price myself, also with other equipment. They're just "switches" and it seems like nothing, but they can be damaged with chemicals and wrong lubricants. With my 576, the lock mechanism, and the sliding part inside, was originally greased with some white stuff. After cleaning, I greased it with silicone grease, but there is one which still sometimes doesn't latch well. As if the lock mechnism is worn out. I wonder if these switches were just purchased standard items, or specially made for (or by?) Tektronix.

Bo Bravo, quick tips



1/ Photos: Excellent! You should create a NEW phot album and name it TEK576 RESTORE etc, then remove your photos from my album.
We Setup iphone for optimum res, exposure, use flash if needed light from 2 dir 45 deg Check photo size and res before you post

2/ Contacts: WARNING Contacts metal of switches may NOT be silver but phosphor bronze, Nickle plated etc. Kitchen silver polish is a VERY strong and corrosive chemical DO NOT USE WILL RUIN PLASTIC AND CONTAMINATE

Use ONLY 91 or 99% Isopropyl Alcohol NOT the pharmacy 70% diluted with water and other unknown ingredients.

Use ONLY electronic grade contact/control cleaner /lube, In USA we have Miller Stephensten, and General Cement,

3/ Lube: VERY sparingly on switch parts that are moving or sluggish.

4/ Qservice: Great stock, fine service, ask the owner about any parts that are out of stock or not found.

Alternative in USA Tektronix Vintage Museum in Beaverton.

5/ Beware the transistor and IC sockets, often oxidized pins cause odd intermittents.

Amicalment,

Jon

Bo, your photos reveal some probe bad practice and other comment on parts, etc.

Please make a separate album, you can PM me with your email address, for a markup of some of your photos

Amicalement

Jon

Jon,
the new album with slightly edited description is now moved here:
/g/TekScopes/album?id=292746

I will now use this place for any additions.

I have more photos in case someone is working on this heavy beauty, but it's too much to upload here, so pm me.

Bo