| Click here to select a new forum. |
| LCIII - Recapped and alive! 12 hours later... DOA |
Posted by: skyhawk3355 on 2024-11-08 06:59:00
Hi All,
I'm either cursed or the cats are effing with me.
I recently acquired an LCIII, tested it, and got no video or chimes. Once I recapped the PSU and the logic board I was getting chimes and the question mark floppy. So i was pretty satisfied for the evening. Today, I go to power it on, no video and no chime. WTH!
Now, there is some medium levels of corrosion around U4 and U5. I've pulled up the Bomarc schematics and can see that U5 is part of the audio system, but not sure about U4.
I've got good voltages coming out of the PSU and have an oscilloscope at the ready. Would anyone have any recommendations as to where to probe next?
See attached a pic of U4/U5
Thanks! |
Posted by: finkmac on 2024-11-08 07:06:26
did you actually clean that area? it looks pretty grody. |
Posted by: skyhawk3355 on 2024-11-08 07:14:31
Yeah, the best I could with IPA and Q-Tips. Should I attempt to de-solder and clean it up? I was afraid of breaking the legs on the ICs |
Posted by: skyhawk3355 on 2024-11-08 10:03:17
UGH! cleaned and re-soldered U4 with no change. While poking around I found a cap that I installed yesterday loose. re-soldered the cap and it fired right up.
Guess the moral is to triple check your own work 😬 |
Posted by: djhaloeight on 2024-12-17 16:33:21
For what it’s worth, my LCIII+ died a few years after being fully recapped. The traces on the RAM address bus had corroded internally, due to electrolytic cap juice pooling there before it was fixed. |
Posted by: robin-fo on 2024-12-17 21:18:29
Isn‘t the LCIII the one with the reversed capacitor? Did you solder in that one properly? |
Posted by: djhaloeight on 2024-12-24 22:20:25
I forgot to mention that max1zzz (who is a serious Mac mad scientist!) very kindly diagnosed the open traces on my LCIII+ and transferred everything from my board to one of his new production boards. That's how I found out it was rotted traces. I'm unaware of any reversed capacitors on these machines. I've also yet to tackle a recap job myself, but I've got a Yihua combo hot air rework/soldering station that I need to set up. I've got a dead LC board that probably has bad traces but I'll give it a go on that before I try the 475 and my working LCII, both of which need caps. |
| 1 |