Electronics > Repair

Tektronix 7613 display and power supply problems

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BlownUpCapacitor:
The scope now works just fine. I glued a piece of scrap metal to the S8050, which does a good job as a heat sink. It is only slightly warm to the touch.

The readout system still sucks though.

I see the trace becoming unfocused at the ends of the trace. In the middle, the trace looks exceptionally sharp, but the ends look blurry. I followed the service manual for Z-axis and CRT adjustments but no further improvement with the unfocused ends.

BlownUpCapacitor:
Scope is now fully operational with readout.

J503 on the Horizintal amp board was not making a good connection with the center conductor in the coax cable. Fixing this solved the readout issue.

Still having a great amount of trouble accessing the A13 rectifier board to permanently implement the capacitor fixes. Any tips on accessing it would be greatly appreciated.

Also plastic bezel is missing on this scope so I was wondering if some one else had a 7613, or 7633 scope to take measurements of the bezel and post it here so I can 3D print a new one. Or maybe such a file already exists and I can not find it yet.

BlownUpCapacitor:
And a new issue has arisen whilst trying to fix an old issue.

The scope worked perfectly fine before, with only one caveat: The -15v, +15v, and +5v rails would drop out randomly and would require percussive maintenance to rectify the issue.

I thought this was due to the TI socket that holds U973 was faulty and wasn't making a good connection anymore. So I replaced it with a machined IC socket.

Now the +5v rail reads DOUBLE at 10.00v The rest of the voltage rails seem to be just fine.

pin 4 of U973 reads +9.8v

anode of CR981 reads +12.89v

I hope I didn't damage U973 as I think that would be a difficult part to source.

nearly 10 volts at the 5v rails indicates to me that Q988 is constantly on, or shorted across collector and emitter, bringing in the almost full 11.5v to the 5v line.

Q985 tests fine with the diode tester. This means it might always be on, U973C may be the cause of that.

U973C might always be on which could be caused by U973E not being on enough.

Edit: Voltage at base of U973E is 4.7v, which means that the transistor should be conducting, and thus bring down the voltage at base of U973C. To me this is indicating a bad IC.

BlownUpCapacitor:
Voltage at emitter of U973E is +8v. So if there's +4v at the base, no current flows through the base which means that the transistor will be off. That tracks, but why is there +8v at the emitter of U973E?

Perhaps U973D is shorted and is giving full voltage from the 5v rail to the emitter, not allowing current to flow through the base of the E transistor.

Anyway, I bodged a 500k pot from the collector of the E transistor to GND. Adjusting that I can adjust the 5v rail and the scope works perfectly fine.

BlownUpCapacitor:
I think the D transistor was indeed shorted because I replaced the entire transistor array with discrete transistors and it works fine now. The 5v rail is spot on.

Here's the transistor abomination if you want to see images.

Found a suitable replacement. Turns out the transistor array was a standard type and not some super custom version. It's equivalent to the LM3086/LM3046

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