Mac SE/30 - analogue/logic board/psu recapped, now chimes but stuck at black screen

[mac_enthusiast]

Hi guys,

I'd be very grateful some repair advice for a Mac SE/30 that I picked up, sold as spares or repair. By way of background, I'm not too shabby with electronics repair and diagnosis.

Although there was no obvious battery damage or capacitor leakage, I've cleaned and recapped the logic board, analogue board and the Sony CR-44 power supply. I've tested the latter under load and am getting the right voltages. On the logic board, I have checked traces and VIAs - none obviously broken or corroded. On the analogue board and video board, which have clearly got quite hot in the past, I've cleaned and resoldered any potentially dry joints. I've also removed and tested some of the usual suspects (CR2,3,4 and Q2) - all appear to be fine.

Currently, on applying power, I get a chime but the CRT stays completely black (even with the brightness knob turned all the way up). I can see a glow at the back so I know I've got high voltage there. The hard drive (40SC) is seized up - a job for another day (!) - but I've connected an RASCSI and from the logs I see that the Mac doesn't get as far as trying to query or boot from an external SCSI device.

I'd be very grateful for any thoughts on what to try next. Sadly I don't have another working SE/30 to use to swap out boards or components. From extensive searching of the forums, I have seen a couple of cases where, even with a working analogue board, a defective logic board can leave the screen completely blank. My guess though is it's a component on the analogue board that I haven't changed yet, as that's clearly where it's got hottest.

Any thoughts would be much appreciated!

Kind regards,


John

 

[thellmer]

I know this is an older post, but had a similar issue on my Se/30 I recapped and turned out I had accidentally shorted a trace on I believe the positive end of C11 to the trace a hair's width from the through-hole. The solder on the top side of the board had barely nicked the trace but it was enough to short it high. The computer was working but it killed the analog signal and even the high voltage circuitry was inoperative on the analog. Wicking the solder off the leg and ensuring the short no longer existed returned the video/raster normally. On the opposite end, if you short the negative end of C11 to the trace running against it, also a hair's width away, you will get the siasma screen and no boot since it prevents the GLUE chip from operating. I had both issues all from replacing that one axial cap :-( All fixed now though.