TC 535P Timer/Multi-Scaler NIM issue - Help is needed

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Arthur Antal
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TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Post by Arthur Antal »

Hi@,

I've here a broken Tennelec TC 535P Timer/Multi-Scaler NIM.

Issue 1:
On channel "A" always will be displayed the channel "A" timer preset seting I set. E.g. on the attached pic, 6 x 10^2. That means, the counter is running from 0 but to max. 600 (or what ever I set as time).
This happens only with applied valid input signal and if the rate is high enough (from a pulse generator e.g.). The same result on both "A" inputs.

Issue 2:
Channel "C" (inputs on the back side) displays approximatly the half value of channel "B" (I use the same pulse on all 3 inputs at the same time).

This modul worked well two years ago, I can recall.
I did a few investigations already, I interchanged the two dual scaler modules (are two the same) in the slots but unfortunately seems that the issue is on another PCB.
All switches checked and works fine. Nu visual issues.I know about tantal capacitor issues in several NIM's from the 70/80's, but here are only two inside and on a common PCB (channel "B" works just fine).

I've a bit of experience in electronics, I've also all needed instruments and tools. I fixed several old NIM's alraedy in my life.
Now my question to you. Do you have any idea how to localize the issue?
On all 3 channels are NE521N (High-speed dual-differential comparator/sense amp) involved as input IC's. Maybe I'll replace the one on channel "A". But I guess is a "digital" issue and not "analog".

Perhaps has somebody the schematic and the user manual for this NIM? I checket already the net but unfortunately no info's about this unit.

I'm very keen to fix this broken guy...
Thank you in advance!

Best regards
Arthur
Attachments
TC-535P.jpg
Last edited by Arthur Antal on Mon Mar 15, 2021 5:24 pm, edited 1 time in total.
John Futter
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Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Post by John Futter »

Arthur
Hoiw about following the rules you signed up for when joining this site
1./real full name not just your first name
2./ first post to be in the "please introduce yourself" forum


please amend
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Arthur Antal
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Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Post by Arthur Antal »

Hi John,

thank you for the hint...
I introduced already myself a few days ago in the mentioned part of the forum.
You're right the user name is only my first name, BTW in my profile I registered with my full name.
I'll fix that now.

Best regards
Arthur
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Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Post by John Futter »

THX


Arthur
Nearly all breakdowns of these modules are due to failing tantalum capacitors that decouple the supply lines to the ic's usually they have the series resistor ( especially so in the ORTEC modules)
check all caps carefully for discoloration they go so short circuit that they do not necessarily get hot the series resistors 1 to 15 ohms also tend to get burnt
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Arthur Antal
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Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Post by Arthur Antal »

Yes,
that was my very first thought too, maybe a tantalum cap is shorted (mostly I smell this (:-)).
As you mentioned, my experience is the same, 90% of the NIM issues are caused by shorted tantalum caps followed by burned PS line serial resistors or inductances.
Here I've to do with only two of this caps, both caps are located in the common stage for all 3 inputs. On the 5V regulator board and the second one near a 555 timer IC on the ADC board. Both caps are OK.

The two scaler boards are also OK, since this are twice the same boards and I changed among themselves and the issue remains on channel "A".
Therefore I guess the issue is on the board nr. 3 or 4 or on the MB (there are also two TTL IC's).

Now I could replace all TTL IC's on the PCB's 3 and 4 (with sockets) until the issue is gone but is not the finest procedure...
Therefore it will be nice to get the schematic. A reverse engineering is pretty time consuming.

br/Arthur
Attachments
TC-535P_inside.jpg
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Richard Hull
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Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Post by Richard Hull »

Dirty pushbutton switches are always an issue. A number of non-coating sprays that evaporate clean should be sprayed on the contact as the switch is violently toggled in and out with some vigor. This switches work the boards telling the boards what to do. Without a spray, many rapid push button cycles might rub away some oxides or sulfides on silver plated slide contacts.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Arthur Antal
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Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Post by Arthur Antal »

Hi Richard,
thanks for the hints. Yes, I know about this dirty (sometimes silver plated "black" contacts) switches.
In my case, I measured with a mOhm meter. Everything is fine, the decade switches too. I really can exclude contact issues.

I replay to your post even though is maybe off topic, but maybe gives other users a few tips, what kind of sprays I use to clean and maintain contacts and pots.

- I use for very dirty stuff the "Kontakt 60". BTW with this stuff you've to be carefull since contains a small amount of Phosphoric acid too (as I know)!
I use after a few hours of action time the "Kontakt WL" cleaning spray (or isopropyl alcohol) to clean out the gunk. Without cleaning, after a couple of weeks you get more issues as before, like greenish contacts...
After this treatment I use the "Teslanol T6 Oszillin" to protect the contacts for long time.
- for sensitive stuff I use only the "Teslanol T6". This can remain after you apply it and you have a long time protection. You can flood the switch, you let to drain out in a convenient position and should be enough.
- the "Kontakt 61" I use mostly in automotive applications to protect the contacts after disasembling something like sensor or board computer plugs, etc. You get a thin protective coating.

I never flood pots with sprays or other stuff. My experience is, you solve the issue only for a time "X". In case of HiFi equipment no scratchy sound on Vol pots after spraying. But the gunk is still inside and soon or later will cause the same issue.
In the 80's we used this method to make the "fast money" before the gig, in power amps, HiFi stuff, etc.
If is it possible, I disasamble the pots and I try to clean and I protect only the resistive track with Teslanol and a Q-Tip. I let the grease around the axis untouched to not distroy the "fain feeling" if you rotate the knob...

All what I wrote is only based on my private experience. Certainly most of you knows all this.
I collect and I repair since about 40 years vintage HiFi equipment, Synthesisers, 8 Bit computers, etc. According to my experience up to now, the Teslanol is my favorite product I use. Unfortunately I discovered this product to late (10 years ago).
BTW, I don't know if the stuff is in every country available. But if you can get a bottle, give it a try (i am not affiliated with the company).

br/Arthur
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kontakt sprays.jpg
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Ed Meserve
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Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Post by Ed Meserve »

Kontakt 60 would make a great addition to the "Prime Sources" forum; 'wink wink, nudge nudge ; )

Ed
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