Tektronix 2230 Scope - Storage Waveform/Readout Display Fault (Fixed!)

[fmashockie]

Hey y'all I am reaching out for some help regarding this issue I am having with a 2230 scope I have been repairing.  Long story short, I may have accidentally shorted something out on the Vector Generator board when I was putting the scope back together (just when I had basically finished repairing the whole thing!!  ).  For those of you who don't own this scope, the Vector Gen board and the I/O board are pratically sandwiched back-to-back within a metal shielding cavity.  Normally, they have plastic stand-offs that keep them separated from one other, but mine had broke so I was trying to figure out a different way to secure them in this shielding and this happened...

It would be easier to just show you (there's a 30 second video on my YT channel showing the fault below) but basically when the unit is in store mode, the signal trace gets cut off or sandwiched at the top and bottom of the CRT display.  This only happens to the waveform in store-mode.  It also happens to the Readout in both store and non-store modes.  So the fault only affects the vector-based displays.  It also seems to only affect the Y Vector.  The trace/readout can be moved left to right off the CRT like normal.

I've tried following the schematic and the representative waveforms provided in the service manual.  Things start to differ immediately at the first JFET op amps (U6303 and U6304) that make up the veritcal and horizontal vector generators.  I measured the output of both of these op-amps (marked 129 and 130 for the horizontal and vertical generators, respectively) and the waveform I get is drastically different than what is provided in the service manaul (see attached photos below).

The inputs (labeled 'X Vect' and 'Y Vect' on schematic) to these op-amps come directly from the outputs to X and Y DACs on the storage board which take analog signals from the digital display controller. 

I was wondering if anyone who has the 2230 (or similar) has seen this issue before and was able to successfully troubleshoot it.  Also, if you have a 2230, if you could probe the inputs (pin 2 of U6303 and U6304) for me and share the waveform on here I would greatly appreciate it!  I am hoping I did not damage the Digital display controller or DACs.  I would assume not because the digital display can still provide the correct readout/signal if they are positioned in the middle of the screen (using the trimmer pots R9222 and R9224 for Store Y gain and Store Y Offset).  But at the same time, it's confusing to me that the output waveform of both these op-amps is incorrect as they are the first component right after the DACs.  Anyway, I would greatly appreciate anyone's help/input/suggestions on this issue.  Thanks in advance!

Here's the short clip of the fault

[fmashockie]

Update:

Fixed!  It was U6401 which is a CA3046 5 NPN transistor array.  Both U6401A and U6401B measured faulty with my DMM diode-test.  I didn't have a CA3046 on hand, so I just made my own with 5 discrete transistors.  And it fixed the display!

Also, the waveforms I shared did not match the service manual because I forgot to put the scope in calibration mode as directed by the service manual.  The waveforms I measured for the outputs to op-amps U6303 and U6304 then matched the service manual.  But there were discrepancies once I got to the vertical amplifier circuitry, which now makes perfect sense!

[factory]

Those CA3046 transistor arrays have quite low voltage ratings, I'm not surprized a couple died when the boards shorted together. Had a few dead in the Tek 244x/246x series too, from PSU failure.

David

[fmashockie]

Yes they do! I attached max ratings below.  There are flyback converters on the input-output board which generate +-15V supplies from the +-8.6V supplies.  These are for the S/H integrators on the vector generator board.  So it could have easily come in contact with those rails on the I/O board. 

I'm just glad it was the CA3046 and not some of the other ICs on the board that can no longer be purchased easily.