Two SE/30 motherboards: one distorted video, one no sound!

[Byrd]

Hi,

I've been busy the past week restoring my dead SE/30 - I have a spare SE/30 machine for parts as well. Both had the Simasimac at startup, so I took about replacing all of the caps on the "good" one (using trag's tantalum caps), removed any residue on the board and put in a new PRAM battery. All went well, and the "good" SE/30 was up and running with no issues..

About a week after replacing the caps, I turned on the Mac and it displayed a garbled, distorted video output, as pictured:

http://img200.imageshack.us/i/img2996w.jpg/

http://img513.imageshack.us/i/img2998.jpg/

http://img405.imageshack.us/i/img2999.jpg/

I checked all caps, which were fine, and cleaned the board thoroughly yet again. I thought I'd try my luck and replace the caps on the "parts" SE/30, which when placed into the "good" SE/30, fired up perfectly, with perfect crisp video ... but no sound. It's as if the sound is disabled as the menu bar flashes black and white when an alert sound is made. Tried external speakers - sound still disabled (and yes sound is not muted under System 7.1). Again, all caps were checked. I suspect this particular SE/30 board always had no sound, but can't remember now.

If I interchange the two boards into the two SE/30 carcasses I have, the same issues occur on both boards - garbled video on one, no sound on the other }

Please: any pointers welcomed! How do I test for a faulty sound IC? I'm more than prepared to cannibalise one board for the other to get a 100% working SE/30

Thanks,

JB

 

[Unknown_K]

Make sure the caps are placed with the correct polarity and value and are actually soldered on both sides. Was there any damage on the board from leaking caps (green residue from corroded tracks)? Are you sure the RAM is good and matched sets (video problem)?

 

[Byrd]

Yes I've switched the RAM in both to no avail, and double checked the caps on both.

The board with garbled video had more corrosion around the capacitor terminals, but no trace damage.

The board with no sound: does appear to have a small amount of green corossion, I will check continuity.

Any chance the video ROM could be corrupt on the board with garbled video (looking at it's removable socket?)

Thanks for your input,

JB

 

[TheoryBoy]

I had something very like what you are getting with the bad video. Turns out I had 2 bad video memory chips, which caused thin vertical bars over the video.

But unlike mine, you are getting corrupt graphics as well. Could be a fault with one of the multiplexers (74F253) since your video is also horizontially shifted/corrupted.

(They were the first thing I swapped) link : viewtopic.php?f=7&t=1047&p=12340