Tektronix 576

RocketMonkey

RocketMonkey

Active Member
Anybody familiar with this thing? I just got one and I'm itiching to mess around with it. It works but its not happy. Im cleaning the controls today and learning the basics about how to operate it. The trace flickers and I think has a problem with loop compensation. With no input i can see a "ripple" rolling around the trace. With a transistor hooked up I have the same fuzzy ripple and a flicker. It does draw the curve. I don't have any fixtures yet so i suppose some of the trouble could be the long bananas but ill keep messing with it.20170429_141308.jpg
 
So here is sweeping the collector voltage up. PNP normal mode.
20170429_141759.jpg
So fully CCW

20170429_141802.jpg
Beginning to roll up. The trace unfolds see how the top edge is pointing left and right edge is pointing down.

20170429_141805.jpg
Now its looking more normal but kinda rough.

20170429_141808.jpg
Now this looks more like what i had expected.

The cables are not causing any of the issues I have seen. I tacked short wires on a to-92 and hooked it up directly so no long leads.
 
Its pulling about 60 watts and the voltage selector is correct. So it appears that all the other supplies use the -75 as a reference. Seems i need to figure out why it wont adjust and/why its low.
 
You may have one or more bad filter caps in the power supply. Look at each one with a scope. The regulated supplies should show a flat line, if there are any dips the filter before the regulator is bad.

Is the -75 right?
 
Good call, There is a lot of 120 showing on the rails. The -75V is the worst.20170429_190952.jpg

Holds a charge pretty good still. Need to make a discharge stick. And of course that one, C707 is buried. The only 80v i have around is way too huge i guess ill roll it up slow on the variac and see how it with a new cap strapped accrost C707.
 
It doesn't take much ripple to screw up the trace. That's a really nice piece of gear you've got there. Congratulations!

I don't envy you the job of getting to the caps, though. I recently helped a friend replace some caps in a Tek 465. I'd rather have my gums scrapped than do that again. :)
 
20170505_101314.jpg
Much better, got the worst couple filters replaced. Still not pretty at some of the lower ranges. Hopefully knocking out the rest will square it away. Its definitely usable now anyway. C707 was a big resistor and a few pF.
 
I put my scope on the 100 V supply because even with a new main filter cap it was doing about 2 volts ac on the meter. I figured I'd look with the scope to see what it looked like, and it shit the bed when flipped it on.
 
Last edited:
Visiting my GF's mom, I'll download the manual when we get home and take a look. Been over 20 years since I've stuck my head into one of these.
 
That was the plan, and Q851 is socketed. I hope the transformer is not shorted out. The only thing I tested before hanging it up last night was ohming out R850. Its a couple k ohms now. Hopefully I'll get a chance to work on it today.
 
Wooo hooo, the coil is not blown. Q850 seems ok also. Thus far just R850 is definitely dead. Now I'm wondering what happened, not feeling just replacing it and firing it back up. I guess I need to figure out how the regulator works and see about figuring out what happened. Might fire it up with Q850 removed and see what is on the base socket of Q850.

Screenshot_20170519-224031.png
 
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