Tekk
Active member
Hey everybody.
I picked up a SE/30 the other day. When powered on, it wouldn't chime, but I did get some horizontal lines on the monitor. Great, this problem is covered on this awesome website, so it should be pretty easy to fix, right? It wasn't.
I first turned to the analog board, and found an open resistor (none of the ones listed as potential culprits on the website, though). Replaced that. Same issue.
I then ordered a capacitor set (thanks trag!) and recapped the logic board, because I figured that might be the problem, and it would have to be done anyway. Woo hoo, it now chimes! Same video problem though.
I moved down the list of culprits on the site. I pulled transistor Q1 from the video board and tested it using my multimeter's hFE function, which showed it as bad. Replaced it, same problem. I then removed IC U1 from the analog board (a 74LS38 quad 2-input NAND trigger) and tested it on a breadboard. Three out of the four gates worked properly, one was stuck at a high logic level. According to this schematic, the broken gate is driven by the video signal from the logic board. Very promising. So, since there's one unused gate on the chip, I added a couple of wires to reroute the signal to/from the unused gate instead of the broken gate. Same issue!!
Here's a video I made (sad mac chimes are because I removed a SIMM; with all 4 SIMMs installed, it does the happy chime).
I'm now out of ideas. Does anyone see anything I'm missing? :-/
I picked up a SE/30 the other day. When powered on, it wouldn't chime, but I did get some horizontal lines on the monitor. Great, this problem is covered on this awesome website, so it should be pretty easy to fix, right? It wasn't.
I first turned to the analog board, and found an open resistor (none of the ones listed as potential culprits on the website, though). Replaced that. Same issue.
I then ordered a capacitor set (thanks trag!) and recapped the logic board, because I figured that might be the problem, and it would have to be done anyway. Woo hoo, it now chimes! Same video problem though.
I moved down the list of culprits on the site. I pulled transistor Q1 from the video board and tested it using my multimeter's hFE function, which showed it as bad. Replaced it, same problem. I then removed IC U1 from the analog board (a 74LS38 quad 2-input NAND trigger) and tested it on a breadboard. Three out of the four gates worked properly, one was stuck at a high logic level. According to this schematic, the broken gate is driven by the video signal from the logic board. Very promising. So, since there's one unused gate on the chip, I added a couple of wires to reroute the signal to/from the unused gate instead of the broken gate. Same issue!!
Here's a video I made (sad mac chimes are because I removed a SIMM; with all 4 SIMMs installed, it does the happy chime).
I'm now out of ideas. Does anyone see anything I'm missing? :-/