68kMLA Classic Interface

Isn’t @pax saying that the full 040 card they have originally came from their 550c, but that they moved it to their 520 when they upgraded the former with a PPC card?

Isn’t @pax saying that the full 040 card they have originally came from their 550c, but that they moved it to their 520 when they upgraded the former with a PPC card?

I've been working on piecing together 4 more 5xx series PowerBooks from various working/not-working machines I picked up a couple weeks ago. Three of them are working but for the fourth, it's a little flaky booting and I noticed the speaker was crackling non-stop after power on. I did smell something - it wasn't the usual fish smell from electrolytic caps but smelled more like ammonia? Not positive. It couldn't be the 1 logic board cap on these as I already replaced it with a brand new polymer capacitor. That's when I spotted:

View attachment 92724

(screen capture from @3lectr1cPPC 's MacDat site).

It's been staring at me the whole time but underneath the two purple plastic boxes are C110 and C111, both seem to be 68uF 20V capacitors. They are metal cans inside the plastic covers but not sure what they are made of. There was residue under both but I can't be sure whether that may have been from the original 100uF 25V capacitor next to them.

View attachment 92728

I pulled them off the board, one of the cans seemed to be bulging on the bottom (next to the pins). Off the board, one of them measured 65uF but the other was around 56uF. That would be at the edge of 20% tolerance and beyond 10% tolerance.

I replaced the lower capacitance one with another off a donor board. The system seems more stable and the crackling speaker seems to have gone away (although I don't have a large enough sample size).

cc: @croissantking

Interesting find - can you cut one open to see if it’s fluid filled?

I cut two of them open, they are dry. Tightly packed roll/layers of black stuff inside, but dry.

So presumably polymer caps, but also potentially dried out electrolytics?

Excited to the see the writeup on the ram mod. I ended up upgrading 2 cpu boards to full 040's this past weekend. I still need to change the crystal.and see if I can get 40mhz stable on these cards. BIG Thanks to the guys that did this mod previously!!! @croissantking and @jmacz. I had to try it since y'all had laid out all the ground work for it!.Mucho Kuddos!!!