Its a pierce style oscillator if i remember correctly

One side connects to the inverter input (high impedance, sine like), the other to the output (lower impedance, distorted or clipped). Different bias, loading, and phase.

In your screenshot, one pic shows a perfecr sine wave. Other leg shows more clipped.

Both show same frequency, but shape and amplitude differ which is exactly what we expect from a working oscillator.

Thanks for that! That's extremely helpful for the situation I'm in. I'll stop worrying that Y3 is a problem, or that is was partially rotted being so close to the UE10 that was damaged.

I took your advice and found a mostly working SE/30 for $375 on ebay, only the SCSI HD/chip/traces are having trouble, it does boot from floppy and has a functioning CPU/board/RAM/ROM, with the Sony CR-44 PSU in it - from looking at the IEC connector in the rear - so it should be a close match to my current one.

I've had some interesting clock signals from the CPU 'walk the bus' test, compared to the Simasima Repair Guide:


Looking forward to comparing signals with the new-to-me SE/30 that's on the way here.

Tried my new TechStep today and it's as I expected, unable to communicate with the SCSI/Serial ports. I have two nice SE's here I can test it with until the new one arrives.

Thanks again @muse!

Decided to press on with the repair guide until my test SE/30 gets here.

In the Video Multiplexing section on page 50, UD8 is missing signals and has distorted wave forms, it doesn't look damaged but who knows if there's electrolytic fluid under there still. UE8 has already been replaced and the signals are present.

Going to replace UD8 with 595-SN74F253DRG4, getting (4) just in case: https://www.mouser.com/ProductDetail/Texas-Instruments/SN74F253DRG4

Also the Video ROM at UK6 is missing many signals, going to get a 556-AT28C64B15PU, just in case: https://www.mouser.com/ProductDetail/Microchip-Technology/AT28C64B-15PU

Already have a TL866 programmer, but can anyone tell me where to get the video ROM binary from for UK6?

After watching this video on how to read the Mac SE/30 UK6 Video ROM chip:

I was able to do the same with my less expensive TL866-3G:
[Image: TL866-3g.jpg]



Had to select the AMD AM2764A chip in the Xgpro 13.06 software, and disable the Options to Pin Detect and Check ID - was then able to Read the ROM.

This tells me there was nothing wrong with my UK6 Video ROM chip. The missing signals at UK6 are hopefully due to the UD8 being bad on this board.

After looking at UD8 for a while with the scope, I've absolutely determined that the signals A0 at pin 4 and A1 at pin 12 are entirely missing, all the other signals at UD8 are present and correct.

I have verified the missing A0 and A1 at UE10 ASC, UK6 the Video Rom and also UI8 the Glue Chip. I have (4) F253 chips on the way here Tuesday of next week, looking forward to replacing UD8.

Regarding my sound being all but gone besides the startup pops and clicks, it's looking like TL071, or Q1/Q2 may be bad, they have corrosion on them fairly badly. Going to order replacements for those once I've done some more troubleshooting with a working reference SE/30 logic board that is set to arrive tomorrow.

Enjoying this fight and won't be giving up until I have (2) completely functional SE/30's.