Waking up an old Tektronix
 

I recently came into ownership of a Tektronix 535 oscilloscope and a few neat plugins however that I can tell it has not seen use for a number of decades.

I have it somewhat dismantled right now as I do some repairs and inspect the stacked capacitors but I'm trying to figure out how to wake the chassis up. Under normal circumstances there is a delay relay that lets the tubes light and voltages stabilize before bringing the rest of the chassis up. I am not sure if I can safely variac the system in this state. Does anyone have suggestions?

On Dumonts that have B+ delay relays I just jump the relay contacts and variac it anyway.

Second the variac motion, bypass the time delay tube but keep in mind the relay may not pull in on the reduced voltage. The bigger problems I recall were with the CRT anode supply and weak HV transformer that was prone to shorting out, a real pest in the 545s as well.

A word of caution: use only a silver bearing solder on the porcelain terminal strips, I've damaged many in my time using standard 60/40 solder

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Let me know if you'd like to buy/trade for my OEM scope cart for that unit. Includes drawer and space for two spare modules.

It's in good shape. Shipping to the northern reaches, and even just crossing the border, will be a hoot, I'm sure.

It's funny, I actually got the cart first and then realized I know someone who might have a compatible scope they were willing to shed.
So I already have a cart for it and goodies like a spectrum analyzer.

https://hosting.photobucket.com/imag...080&fit=bounds

Update: Yeah it came up alright. Had to oil the fan and reseat a few tubes but no smoke and no bad noises. Just a gassy 12AU7A.

Be sure to scrape of the carbonization on the ceramic strips in the HV section.

I'll do that after I deal with tube issues that surfaced after I installed the delay relay. I got one that was visibly gone to air and another that turned up gassy once loaded.

https://hosting.photobucket.com/imag...080&fit=bounds

There was also another tube I didn't notice before that was completely missing.

Looks good, my Tektronix 516 has a lazy fan too.

I actually constructed an audio amplifier with parts liberated from a dead Tek-545 scope, time delay tube and the 5751 reference feeding the triode regulator.
Sadly time and several generations of mice have taken their toll after spending the past 13+ years in an underground storage bunker so now it's in rough shape.

Here's the chassis from 2005.

Arc Tech-109

Okay hella bump time but my shipment of replacement 6BQ7A's and another 6AU5 arrived so now we have a scope fully loaded down with what should all be good tubes.
https://hosting.photobucket.com/imag.../CGS_10822.JPG

Still no trace. :thumbsdn:

With all the tubes in place and lit as soon as the delay closes I get a beam flash in the upper left of the display and then the beam finder arrows say there's something tracking left to right (the speed of which changes relative to but not exactly with horizontal sweep time) and even when I vertically center the control I don't see anything. Yes I can see neck glow.
The reason I got a spare 6AU5 was as soon as the delay closed the one in the high voltage section would light the glass a dull blue and after five minutes or so you could see it starting to redplate. The replacement tube should be good but when swapped does the same thing.
https://hosting.photobucket.com/imag.../CGS_10823.JPG

Yep, did that once, but can't recall why, as Motorola and Zenith had instrument repair/calibration departments that normally were the only ones to access the insides.

There should be a small spool of silver solder bolted to the chassis somewhere if no one has stolen it.

A lot of our scopes had a burn spot at the lower left corner of the graticule from using them to do X-Y plots of device safe area (I vs. V) and forgetting to turn down the beam.

No that roll of solder is long gone. I don't think I've ever gotten a tek scope that still had it hiding away inside.
Regardless I keep a roll of silver solder buried for special occasions.

MIPS, have you made any more headway in getting this beast running?

Nope. Still got the problem with the beam vanishing off the screen and not coming back. I rolled the cart into storage for the winter so I could clear the bench for a few other outstanding projects (Rebuilding a pair of Motorola MDT's, cleaning an IBM 029 keypunch and cleaning a umatic deck) but if someone has some awesome pointers on where I should be poking and what I should be seeing I'll roll it out before the snow melts and check.

My Heathkit IM-12 was sort of like that. It was a few bad capacitiors around the vertical horiziontal positioning controls. There would be a trace for a few minutes and the it would creep off the screen.

The neat thing is this scope has neon indicators telling you where the beam is so you can use the controls to locate it and center it. The problem is that often I can get all four directional indicator lights out and there is still no beam, but it is sweeping because I can enlarge the scale until it overscans and you can see the left-right indicators flash in sequence.

It kind of sounds like something in the high voltage is being overloaded with the red plating tube in the HV. Shorted cap?

Have you checked c805 and c806 in the hv supply?

jr

They test fine for capacitance and resistance out of circuit.

Now one thing I have not done is test voltages to the schematic. I was planning to do that after I cleaned the chassis but COVID got in the way. Hell now that I think about it I have not even cleaned the tubes yet.

Edited: Oh well that might also do it. Pin 1 on the 12AU7 stayed in the socket when I pulled the tube out.

It would be nice if that's all that's wrong.

It would explain what is wrong with the beam sweep because with pin 1 completely missing you are missing a feedback loop for the HV oscillator.
I'll have to dig around and see where my spares went.

My used spare read weak emission but I have a 12AU7A that tests like new so I threw that in.
Well now I can see a sweep but it still cuts out.

https://imgur.com/59uwUnp