Tektronix 577 D1 with storage tube repair and restoration help. FIXED !!

Ok I Pulled P120 and lost the +12 short on the Main board. But still had the +5 volt short.

So I went to investigate the +12 short of 19.6 ohms on pin 2 of P120.

I need to look for that lamp on the schematic.

I found that the Collector supply disable lamp reads 19.6 ohms to GND. So I went back to the main board and I think the Lamps in series there also are the "short" we see on the +5 line.

So I might have been chasing my tail here?

Im not as experienced at these schematics as others are can someone confirm my findings?

EDIT: I lost the 53 volts. At connector P392, pin 1 and 5 I have -23.XX volts and on pin 4 I have -75.x !! Ugh!!!! This thing is possessed ! lol

Thanks,
Athanasios
 
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Vint Age said:
Yes indeed! :whip:
:biggrin:
Click to expand...
Would connecting the 177 fixture while the 577 was powered possibly cause a failure? The 177 was out a bit and the collector supply light was on and I pushed the 177 back in while it was powered up.
Wonder if that could have cause some damage in the 577 and the 177. :whip:


EDIT: Asked google and its AI agent said yes this can damage the floating power supply and other things in either unit! Fu<k !!!!

Nashou
 
Not sure what is going on with this "Carrie" unit but I have the -53 volts back on pin 4. what I notice is if I press the Polarity button it drops at pin 4 and then goes to positive at pin 5 on P392. I think this is normal tho.

Athanasios
 
Well , things are definitely wacky with this unit. Lost the -53 volts at the collector of Q386. But if I press the polarity Normal button to be out it becomes
-53 or there about . But that doesn't coincide with the set up at the beginning of the section for what the voltages and waveforms should be with the dark grey buttons all pressed in except for the repeat button. This voltage comes for the PS board. Can Bridge rectifiers act up and sometime work properly and some times not?

Any how I took note of all the voltages on the chips on the A1 main board, well most of them.

here they are, maybe someone can help me see something I'm missing, some or off but not by a lot.

55125528531_9deeb3bdf6_b.jpg


55125719398_f65492103c_b.jpg



Thanks in advance

Nashou
 
Ok U380 was acting up. Put new one in and I now have the -53 volts consistently on the collector
of Q386.

But still no waveform at TP360 or TP305.

Nashou
 
Ok I need someone with a 577 to verify something for me. On mine I have a wire from P611 on the main board that goes to the 8th pin from the right on the 177 test fixture.

I think this should go to another pin. But since my unit is one of the earliest made Im not sure.

55146912392_0fd7301dfc_b.jpg


Need to see where there is continuity from P611, pin 1 to which pin on J110 test fixture blade socket.

Athanasios
 
Found something else. My units board is not like the picture in the Sm, we established this earlier. But on The Sm pic I'll add below, Pin 1 from P524 and Pin 1 From P611 are connected. on mine Pin 1 of 524 goes to Pin 2 of P611.

55148159649_adafec5eba_h.jpg


And my board .

55148079233_e1472c7f92_b.jpg


Confirmed in SM

1773539110637.png

If my main board is wrong then I think the Test fixture Socket is wired up wrong. I'll need to remove it to see the number and letter labeling on the socket itself.

EDIT: Also my board P524 is only 8 pins not 9 like in the SM we are using. Ugh . need to find a clear copy of my units service manual.

Athanasios
 
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Did some more exploring last night and I think the blade socket for the 177 is wired correctly . I noticed that the letters skip a few on the schematic and thought on the socket that those letters would be there, but they are skipped there as well.
 
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Also i noticed here in this snippet from the Step Amp Board #3 schematic

55083636921_375194f736_c.jpg


That Pin 2 from P524 and Pin 2 from P611 should be tied together. on mine they are not. Further more there is 9.6 volts on pin 2 of P524 now going to pin 1 of P611. Wonder what issue that would cause?


I also went to Vintage Tektronix Product Repair and dropped them a note
about my board and if they had a SM for that year. They asked me for my Board Version number.
"Give me the part number on your circuit board. It will be a 9 digit number. It could be a 670-, 671-, or 672-. There will also be a raw PCB number that might be a 388- or it might have a letter like JA- etc."

So lets hope I can get some answers from them :)

55150757067_57ddace928_c.jpg
 
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Been e-mailing back and forth with the guy from the Tek Museum and I think I might have a prototype board in a Production made unit.

He's going to look at microfiche manuals to see if he can dig anything up.

Athanasios
 
No Luck with the older schematics from Tek Museum .

I started two threads, one over on TekScopes and the other other on EEVBlog.

lets see if I get any new insights there.

Oh......And I have another 577 coming in that they accepted my low offer on the bay, they said it powered on but had a smell of
strong smoke and they no longer messed with it after they quickly shut it down.


1774552889437.png

more torture for me ;)

Athanasios
 
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redk9258 said:
RIFA cap?
Click to expand...
I don't think there are any in the unit of this thread. But maybe there is in the one on its way as it's a newer serial number. I have a feeling it might be a resistor. I found a few cooked in my unit.

Athanasios
 
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Woo hooo !!! :banana::banana::banana:

mawyatt(Mike) over on eevblogs is the man!!!!

He had me do all these steps and we narrowed it down to CR321 , I changed CR322 I found shorted but never thought to look at the other diode on the schematic right next to it, but in a further location on the actual board !!


well here are the elusive stair step patterns I was looking for at TP 305 !!!! yes !!!:rockon:

55180968123_aba0585e18_b.jpg



:D
 
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Ok here I will try to document the process to find the fault that mawyatt ( Mike) helped guide me through. He definitely is an EE as he described how the stair step generator works. Still a little alien to me but it helped be grasp things better. His comments I will put in italics.

Schematic snippet to follow along.

55182747684_82fc82d3ee_b.jpg


The stair step generator works by periodically pulling charge from the integration capacitor C306 with C279 (or C280) thru diode CR330, then resetting the capacitor with Q306. Check the op-amp U305 and shorting/resetting transistor Q306 across the integration capacitor. You can check with an LM358 and 2N3904 respectively just to see if these components are OK. The other 1/2 of U305 acts as a comparator with a threshold set by Number of Steps pot R315, this triggers flip-flop configured U220 to reset the steps thru Q306.

I didn't change the op amp or the parts he suggested , since I already tested them just before .

He continues .....

Check that you have the proper waveform as shown on U270 pin 3 or 4, then follow the signal on output pin 6. U270 is a one-shot. Then follow thru Q276 and so on.

So I posted some wave forms , here is one example,

55179685898_acd46dd1db_b.jpg


He replied with this ......


See if you are getting a pulse train at the collector of Q276. Then check across R279 (CR330) in both X1 and X.1 Step Amplitude. With the switch set as shown on schematic (X1) Q276 collector is connected to schematic left side of C279. This pulse pulls charge from C306 thur CR330 causing the steps to increase. The right side of CR330 is held a virtual ground by U305A with an offset set by R300 network.

If you remove Q306 then TP305 should ramp up to the rail.

If all this behaves as expected, then U220 or components around such is/are possibly defective.

BTW please label scope traces directly on image.

I didn't label the pics right on it , I usually add a comment below it, but I began to label them for him right on the pic. :(

So here are my results labeled on the pic and reply ;)

55178939817_780f29b7b3_b.jpg


55180236820_977fdd875e_b.jpg


55180266170_31dff1201a_b.jpg



55180129799_8f22a97b0b_b.jpg




And finally with Q306 removed testing TP305 with DMM I get +10.82 volts

With it installed I get -.012 volts
 
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He replied ....

Those look OK. Using Scope Dual trace look at Q276 Collector and Q306 base, use scope DC coupling.

My Reply ......

Had to use a different scope, the 2335 was acting weird trying to look at two traces.

55180631634_2e9922fdfa_b.jpg
 
Next in his suggestions ......

So looks like Q306 is being reset every input pulse. Keep the probe on Q306 and look at pin 8 of U305 with the other trace. Also make sure the Rep button is pushed in, and is not in the Single mode.

Also check voltage on pin 3 of U305 and vary Number of Steps pot, this should range from ~4.7 to ~0 volts

On a MC1458 pin 8 is the + voltage in, maybe you meant pin 1? The schematic for some reason does not show pin 1 labled but instead the voltage pins
8 and 4.

I'll probe pin 1 .


Give me a minute.


Pin 1 the output. Eyes are bad and schematic is hard to read. BTW ignore the Edit: Reset comment, we just removed it.

Going to turn our Tek 577 on make some measurements to compare with.

Here's what we see.

tektronix-577-d1sn-b010116-very-early-model-no-stair-step-seen-on-scope


tektronix-577-d1sn-b010116-very-early-model-no-stair-step-seen-on-scope




I didn't understand what you meant by the reset anyhow lol

Here are the traces, on pin 1 you can barely see some spikes in the trace line.


55180726844_746e248dfc_h.jpg



Check collector of Q324 like above.

Also check voltage on pin 3 of U305 and vary Number of Steps pot, this should range from ~4.7 to ~0 volts. If you don't see this voltage on pin 3 of U305, then check the connector P335 to pot R315. Pin 6 is blue and pin 7 is purple, pin 6 should read 4~5 volts, pin 7 should vary with pot setting. Also check the voltage on pot R315.


Will check , I forgot to mention I do get voltage adjustment on pin 3 from 0-4.7

That's good, then see if you get a trace on Q324 like above, and U305 pin 1. Also do you see the same trace as TP305 on U305 pin 2?

No trace on any of those points.

As a test remove Q306, TP305 should go to + rail and drive U305 pin 1 to the negative rail.

Ok the test went as you said , TP305 went +10.8 and pin 1 went to -9.5

That's good so U305 is behaving as expected. Now try replacing Q306. Before to replace Q306 what's the voltage on U220 pin 9?

.009, with and with out Q306 installed

Ok, what's it with Q306 installed? Turn Number of Steps pot to max.
The same

Turn pot to max, what's it now?

Which pot? And do this with q306 installed?

Yes Q306 installed. Turn Number of Steps pot to max.

What's the voltage on U220 pin 9?

Same, .009. Tested all pins and nothing happens on all of them.

OK. Either R321 is open, CR322 shorted or U220 pin 9 shorted to ground. Most likely is CR322 shorted.

Remove U220 and measure again.
Then measure R321.

I got 3.5k

OK, this hints at a disconnect between U305 pin 1 and U220 pin 9. Measure between them with an ohmmeter.
As you force TP305 to ~0 volts and + rail, pin 9 of U220 should range from +5 to ~0 volts respectively.

Try this. Without Q306 in, TP305 should be + rail, and pin 9 U220 should be ~0 volts. Then place a clip lead across C306 and TP305 should be ~0, and pin 9 U220 should be ~5 volts.

Ok TP305 went to 0 and pin9 still was 0 :(

So I assume I should replace U220 test again, and the if P9 goes to 5 volts re install Q306?

It's getting late what did you measure under both conditions, removal of Q306 what was U220 Pin 9? The shorting out C306, what was U220 pin 9?

Pin 9 was .009 vdc with c306 Shorted AND q306 removed. I didnt do it with one and then the other, it was done together.

This is getting strange!!

Do the same test again and also measure U305 pin 1. Test meaning removing Q306 and making measurements, then adding short and making measurements.

ok short removed on C306 and Q306 removed:

TP305 10.81 vdc
Pin 9 on U220 .009 vdc
Pin 1 U305 is -9.5

Short added and Q306 is still removed:

TP305 -.009
Pin 9 on U220 .009 vdc
Pin 1 U305 is +10.48

Athanasios
 
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