So, I have finally started trying to salvage the LC form factor machines from my shop haul last December. I was able to get two boards that weren't destroyed by the battery or flooding. Unfortunately, neither would initially boot. On the first, I was looking over the board after my recap, and realized the resistor at R85 was blown in half.
No big deal. I had an old LC III board that had a similar 6.8Ohm resistor. I was able to swap it out and the machine booted with a chime (no video, but I forgot that this machine, like the PowerMac 6100, needs a PRAM battery to boot with video, or you do a quick power off, power on right after the boot chime). So, success!
The second board, I hadn't recapped yet, but plugged it into the Power Supply to test and after a couple of seconds, I noticed the resistor at R85 was smoking a bit. When I looked more closely, the solder had liquified it had gotten so hot. So, that's not ideal. I looked at the area, and noticed the cap at C161, a tantalum, looked to have a bit of a brown discoloration on the right side (I didn't get a picture). But, given that tantalums often fail open, I removed the cap, and tested with the multimeter. Sure enough, it had failed open. Unfortunately, the tantalum on the previously scavenged LC III board didn't look too good, but I had an electrolytic 10uF 16v cap that fit. So, a few of things:
1. If anyone runs into problems with their LC475 / Performa 475 / Quadra 605, I'd take a close look at that corner by the sound chip. I saw someone else needing to replace R85 in another post, so it seems like it may be a common failure.
2. Any thoughts on whether the electrolytic cap I put in will cause any long term problems due to the differences between it and the stock tantalum. Did Apple have any reasoning to why they used tantalum vs electrolytic on these older boards?
3. The resistor at R85 likely got cooked a bit during the process, do you think it's ok or should I try to replace it?
Thanks!
No big deal. I had an old LC III board that had a similar 6.8Ohm resistor. I was able to swap it out and the machine booted with a chime (no video, but I forgot that this machine, like the PowerMac 6100, needs a PRAM battery to boot with video, or you do a quick power off, power on right after the boot chime). So, success!
The second board, I hadn't recapped yet, but plugged it into the Power Supply to test and after a couple of seconds, I noticed the resistor at R85 was smoking a bit. When I looked more closely, the solder had liquified it had gotten so hot. So, that's not ideal. I looked at the area, and noticed the cap at C161, a tantalum, looked to have a bit of a brown discoloration on the right side (I didn't get a picture). But, given that tantalums often fail open, I removed the cap, and tested with the multimeter. Sure enough, it had failed open. Unfortunately, the tantalum on the previously scavenged LC III board didn't look too good, but I had an electrolytic 10uF 16v cap that fit. So, a few of things:
1. If anyone runs into problems with their LC475 / Performa 475 / Quadra 605, I'd take a close look at that corner by the sound chip. I saw someone else needing to replace R85 in another post, so it seems like it may be a common failure.
2. Any thoughts on whether the electrolytic cap I put in will cause any long term problems due to the differences between it and the stock tantalum. Did Apple have any reasoning to why they used tantalum vs electrolytic on these older boards?
3. The resistor at R85 likely got cooked a bit during the process, do you think it's ok or should I try to replace it?
Thanks!