Tektronix 545B Restoration

[Domokelly]

Hi everyone,

I Just thought I’d share my experiences bringing an old Tek 545 B oscilloscope back to life.
I picked this up in early 2020 and decided it’d be a good side project. It was in reasonably good condition when I first got it- had no major damage and the front panels weren’t too heavily marked. However the side and rear panels had a few dents and scratches- plus the paint wasn’t in great condition so I decided that a re-paint was due.

So without going into too much of a diatribe- here’s what I did:

1. Tested all electrolytics for capacitance, ESR and leakage.
2. Clean the tube bases and pins with isopropyl / deoxit
3. Clean all rotary switches with deoxit
4. Clean the rear fan motor which was stiff with old oil.
5. Test / replace transistors.
6. Strip old paint from the panels, spray with etch primer then topcoat.
7. Re-chrome handle clips and tube bezel thumb nuts

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[Domokelly]

So first up- capacitors.
I didn’t have a way of testing leakage of 400V + caps, so I built this unit from SiliconChip.com.au and it’s terrific. It’ll test and reform caps from 11v to 630v in 11 standard increments with a user selectable time from 10 seconds to 60 minutes. As suggested in the instructions I installed it in a plastic parts box which means that it’ll only charge when the lid’s closed- and when it’s open it automatically discharges through a resistor network.

The kit includes the PCB and a pre-programmed PIC and downloadable instructions. It's very well designed and produced and ships from Sydney. I bought the remaining parts from Mouser. Highly recommended.

[Domokelly]

So using this unit I was able to test and reform around 50% of the caps- but most of the LV caps had high leakage and I didn’t want to risk overloading the un-obtanium Tek transformer.

So I decided to replace those. I looked at re-stuffing the original cans but decided the best option were these terrific PCBs from M2 Circuits. They allow you to make combinations with 6mm caps with plenty of ground pin locations and an option to ground the chassis or not. They come in the standard 1” and 1.375”.

https://msquaredcircuits.com/shop/

[Domokelly]

Msquaredcircuits.com 'Multicap' boards installed in the low voltage section:

[Domokelly]

The rest was all pretty straight forward- cleaning switches with deoxit, cleaning the bases and tubes and I tested and replaced a few transistors. Matching the specs of the original germanium transistors was tricky but I managed to find a few online.

So after a lot of checking and rechecking I decided to power it up- and straight away cooked a resistor in the LV section! Unfortunately I’d connected one of the caps in reverse but managed to shut it off before any damage was done. So after re-connecting the cap and the blackened resistor it was back up and running.
The time delay tube kicked in on schedule and there was a promising green glow on the screen.

The only problem was that I couldn’t get he trace to appear on the screen and was constantly shown as being below the screen by the neon position indicators.
I don’t have much experience with high voltage stuff- and for this scope low voltage is +500v! So after a few calls I took it to Gerd at Control Electronics here in Sydney. Funnily enough he had his own 500 series scope and a ‘known good’ plugin, so within a day he’d given me a call to say it was up and running!
Apparently one of the germanium transistors I bought online was faulty- and that was pretty much it.

He's a terrific guy- and he sells used test equipment through his site here in Sydney.

http://www.controlelectronics.com.au

It had an issue with the ‘B’ time base which I worked out was a problem with a rotary selector- and that now seems to be sorted.

Then after that the final step was the cosmetic stuff. I stripped the paint with chemical paint stripper, then pressed out the creases and dents, gave it a light sand to get rid of sharp edges and high spots and primed with with etch primer.

I read a lot online about the difficulty in matching the Tektronix paint colour especially in early Tektronix scopes, so eventually settled on 'Krylon Bahama Sea'. It's definitely lighter than the current Tektronix blue- and lighter than the paint on my 564B. But the final result looks half decent so I'll stick with it for the time being.

The final step was to re-chrome the handle clips and the thumb screws that hold the screen hood in place. The scrome had started to chip off so I figured that re-chroming would be the best option. I used a guy in Liverpool, NSW called Luke from Metal Polishing & Chroming. He does terrific work and is a top guy to boot- plus he's happy to have parts mailed to him. Highly recommended!

https://www.facebook.com/pages/category/Automotive--Aircraft---Boat/Metal-polishing-and-chroming-334106321552/

So it's all done now- but it does still have a problem with the triggering. I can't get it to hold the waveform so there must be a problem in the triggering circuitry. I don't have a way of testing the tubes yet (which has been very lucky so far) so after speaking to user 'VK5RC' who had also restored a 545- I bought a uTracer on his advice. Here's his post:

https://www.eevblog.com/forum/repair/restoration-repair-of-tektronix-545/msg1018767/#msg1018767

I'm yet to build it but I'll test the tubes in the triggering circuit and then I'll go from there. The same problem exists on both the A and B channels so if anyone has any suggestions then I'm all ears!

Anyway I hope this might be of interest to anyone with a similar scope or who's thinking of a similar project.

Cheers, Dom.

[Domokelly]

More pics.

[Domokelly]

Video link:

Sine test pattern- shows the issue I'm having with the triggering. This is as close as I can get to a stationary waveform unfortunately- so fixing this is the next job.




And a Lissajous pattern... because why not.

[andy2000]

Nice job! 

I've just started restoring a 545B that I found at the side of the road in my neighborhood.  I spotted it while going for a walk at night, so I went back with the car to pick it up.  It was bulk trash collection the next week, so I was lucky the scrap metal scavengers didn't see it first.

It was in decent condition, but missing all of the tubes, knobs, and transistors.  Someone also removed the delay time control and the large power resistors on the sub chassis near the fan. 

Fortunately, I had most of the missing parts in my stash, and borrowed a few parts from a mostly working 543B that was planning to restore.  I've already replaced the borrowed parts in the 543B, which I plan to sell when I'm done with the 545B.

Only one of the can caps was bad.  It still has some issues, but it has a sharp trace and will display a waveform.  The main problems are that the A time base doesn't work at all, and it won't trigger in any mode. 

Both the 543B and 545B have bad HV transformers which only work for about 20-30 minutes due to the epoxy potting.  It sounds like you were lucky with your HV transformer.

I thought about rewinding it, but then I had the idea to try modifying the HV transformer for a 545A (I found some cheap ones on ebay).  The 545A uses wax insulation, and doesn't go bad with age like the 545B.  The transformer is almost identical, except for the physical design of the terminal board, and it supplies -1350 and +8650 instead of -1700 and +8300v.  Since the overall potential difference is 10kV in both cases, I don't think it should matter.

First I tried installing one in the 543B as an experiment.  I had to adjust a couple of resistor values to get the HV adjustment in range, and to get the correct grid voltage.  So far it seems like it will work.  The only minor issue I noticed is that the +8650 sags a little at high brightness.  I think that may be unrelated to the transformer swap because the -1350 stays right on the dot.  It may be as simple as a weak HV rectifier tube.  Even if not, it only happens at very high brightness, and it's hardly noticeable. 

[med6753]

Looks good.  I've restored well over a dozen vintage Tek scopes including a similar Type 535A and I'm currently fighting with a Type 547 that has a nasty PSU issue. I'll give you some of my perspectives and experience.

Yes, the paint that matches the Tek blue the closest is Krylon Bahama Sea. It's not exact but it's much better than banged up and scratched covers.

Reforming capacitors. IMHO is a total waste of time. All major electrolytics get replaced regardless if they test good. If I can work around the original can and install new caps that's the preferred method. If not the can is removed and new caps are installed on terminal strips. Some may say that destroys the "vintage" look of the instrument but reliability and function are priority. Besides, it's under the covers and I do my best to clean up and restore the exterior.

Re-stuffing the original aluminum can with new capacitors. Frankly I don't have the patience for that but if you do go for it. Also, I didn't know those adapter boards were available for 500 series. I have used them on 465/475 and they work great.