My New Tektronix 576

[tranguru]

I was soooo jealous of all these guys like Tony X-Ray, Zenwizard, Alan Wolke (W2AEW), and more on Youtube. and their Tek 576.

So I decided to bring one back during my next US trip....from Belgium.

Finally a trip was planned to Phoenix in October. I found a 576 on Ebay for $525 - parts only unit. I did not want to pay too much as the overall risk of ending up with a boat anchor. took me a week to decide yes, no, yesssss, nooooo, ????..

Finally on Thursday night in my bed, with wife already asleep - did not want her to know, I decided to buy it - I only live once and its only money and my birthday is soon, ...in 8 months, ... xmas is closer.

I also had to keep the shipping costs down ==> I would have to take it a checked luggage on my flight back. Otherwise, I would have to pay several hundred bucks on shipping from US to Belgium + huge customs costs as customs would take a look and estimate the price based on google search ==> several thousand dollars ==> high import duties. But weight in the US was 80 pounds with the packaging.
So I had to reduce the weight ==> I looked at youtube videos from Zenwizard and came to the conclusion that the collector HV transformer had to be removed. so I took all the required tools with me.
The 576 has 4 transformers ( Main, collector HV, CRT HV, variac).



The 576 arrived as planned to my hotel. perfect box size, it fit the airline guidelines.
The first topic to solve was the weight - max is 70 pounds. the Unit + box was about 80 pounds.

Step 1 - Play
Play around with the unit and see what works .... nothing worked. one the relays inside did not stop buzzing.
some of the rail voltages where present.
Good news was that I had a later model with the black very HV transformer for the CRT.
But no trace ....

Step 2 - work to lose weight
Get the collector HV transformer out - about 10 pounds (5kg) and the variac - another few pounds.
I couldn't access the transformer leads, as anticipated, with a soldering iron ==> I had to cut them off....
the HV transformer. the idea was that the transformer would just drop out... took me 2 hours to get it out.
I realized my later that there was a much better and elegant solution ... but that comes later.

Step 3 - get ready
Repack and make it easy for the luggage staff to carry the box, not break their back and not drop the box .
So I went to a hardware store to buy duct tape and some rope.
Closed the box, the unit had been foam packed so perfect box fit and no wiggle room in the box.
wrapped the rope around the box and made some kind handles with it.
Boxed weighed about 65 pounds on the hotel's dodgy weighing scale.

Step 4 - check
Make sure airline accepts it - so I went to airport the day before to check- they weighed it ... 69 pounds.

Step 5 - go
Next day 10 am I arrive at the airport. they did not even weigh the box...off it went.
Now I could only hope for the best - 3 legs (Phoenix-Denver- Munich-Brussels) - I bought some perfume on the way back

Step 6 - Pray
At every boarding I could see my box... the rope was all over the place, no more handles...

Step 7 - arrival at Brussels airport
The box was so unusual that I had to get it from the luggage claims desk... had to wait 15 min for them to get it... it finally arrived - and....
.
.
.
.
.
.
.
.
no damage to the box - so far so good

Step 8 - customs
how was I going to go thru customs
option 1 go to items the declare path and tell them I had nothing to declare - after all the unit was not working and parts were out - so no commercial value. but other course there was the risk they might not accept
Option 2: just walk out, with a straight face and hope for the best. with risk the officer stop me, then I would have to explain , and if they don't accept pay a fine on top of the import tax.

I opted for option 2 - sweating a bit for those 20 or so meter walking past the officer

step 9 - drive home
really.... issue at almost every step - the taxi driver refused to take the box
so I had to order a Uber van....any I got home after 20+ hours

Step 10 - the wife
- "what the hell did you buy this time". I gave her the perfume
US TSA had cut the box open to check and had cut the rope (will know for next time)- they closed it put really well with tape- great girls/guys

Any way the baby made it home w/o damage.

Next steps - bring it back to life...

 

[Lou F Quincy]

I admire your optimism.

 

[tranguru]

Next steps - the repair

Step 1: put the two transformers back in.

the Variac was easy.

the collector HV was difficult, because the bolts are in the collector voltage assembly (was easy to unscrew though) and the lead are very short ==> I lengthened the leads and isolated with heatshrink and soldered back to the transformer and also used heatshrink in case the cable come loose.
But how to control the work.... by removing the CRT which I thought would be very difficult - was super easy... that is when I noticed that the collector voltage assembly is actually one assembly including the transformer. I had i know I could have done that in Phoenix already. The front panel knobs are coupled with coupling shafts that be unscrewed and there are connectors to main chassis - of course actually, no way they would assembled this part in one step, it could on have done as a sub assembly and they easily mounted into the main chassis. the CRT comes in last anyway...will know for next time. you can see that clearly on picture 3873. you can see the top view on 3794 with heatshrink, and all the chassis mounting components.
Anyway - I was happy once that was done. turned it on and..... no white smoke. Unit behaved just like in Phoenix.

Step 2 - investigate
In Phoenix, I had measured some voltages and could not find the -12,5V rail and assumed it was dead. it is used in the CRT HV. but actually it is was OKish -11V
I started playing with all the knobs, till I touched the invert knob and ... I had something appearing on the screen very briefly (sorry no pictures - I was too excited).
So I insisted in that area. and progressively the trace appeared but was very unstable.
I put a transistor on the test fixture... only forward current and voltages seemed to more or less work.
No Steps though.

Now I was quite confident I had a chance I could get the unit running again. I came across Jac's Tek 576 pages - https://jacmusic.com/Tube-testers/TEK-576/Tek-576-2-Restoration.html
He had the same issue and found the 5V rail to be the issue
So I made some more measurements. and the 5V rail seemed ok with the DVM, then I took my scope

 

[tranguru]

and see picture Tek_v1.

so issue was clear - without that nothing was going to work. Jac changed the 11kuF cap - ZenWizard had had the same issue and replaced all the filter caps.
I removed the tube and changed all the caps.
long process.... I made adapter PCBs and mounted riveted leads , I had to remove the CRT again, see the pictures. I took a lot of them to make sure I solder them back correctly.
the PCB... should have investigated more the PCB Zenwizard shows in his 576 restoration video.

 

[tranguru]

I checked the 11Kuf cap - like there is no cap.
all the other caps were good. why was this one bad? and many people report the same issue,

the PCB picture are below

 

[tranguru]

and ...

 

[tranguru]

Then the invert button...
Jac had removed the boards and the dismantled the Invert push button.. so I tried the same, but I could get the last board out because of the cable harness behind it (see 0244), I would have had to take a part of the chassis apart - again many pictures to make I put all together again....note that the service manual is super clear also.

Zenwizard recommended Isopropyl Alcohol - I bougght together with Kontakt WL (to be used normally after Kontakt 60 and before 61) - anyway.

it seemed to work so I decided to leave at that.

 

[tranguru]

Step 3

checked voltages with high precision.
mainly the -75V main reference voltage. got it spot on.
all the other voltages seemed to be better also after the 5V rail was fixed - see scope picture - quasi no more ripple.

 

[tranguru]

Step 4

put the unit fully back together

one Major piece of advice: take it very slow and triple check each step

Great thanks to Zenwizard, Jac and Alan!


One point I forgot to mention is that many of the rotary shafts become very hard to turn.... I sprayed them with WD60, Isopropyl Alcohol, till they work again.
this is a typical Tek issue - just look on Ebay at all the tek equipment that has only the inner mounting ring left...

My next step will be to calibrate the unit.....

 

[tranguru]

I admire your optimism.

Optimism ... - Jealousy made me do it - I have to be honest.
I already have 577. so I not sure why I needed this