Powerbook RAM expansion card modifications

TrueNorthStrong

Well-known member
Took a while since I didn’t have any orders to submit but I finally got around to buying some caps and filled out all spots marked for decoupling caps. Only three pads but they’re all filled in. I bought a size too small so they were tricky to get in but it’s done. R2 was removed (measured 33 ohms before removing).

Unfortunately no dice. Still getting death chimes on boot. At this point I can only imagine that I’ve killed a chip or two while soldering them down, so now the work of sorting out which one it is doesn’t sound like fun. I guess it’ll be good practice with the hot air gun.

Any other easy things to check before I start down that path?
 

croissantking

Well-known member
Let's assume it's a bad chip since you say you checked your solder work, and 100 series PSRAM is very fragile. Go easy with the hot air gun, as I've managed to kill a few chips with one. Better to use low-melt solder, if possible.

The RAM is arranged in banks of four 512K chips. Take off the RAM one bank at a time (so taking the capacity down from 10MB to 8MB, then to 6MB, etc) and see at what point it starts to work. When it does start to work, you will know that the most recently removed 2MB bank contains at least one bad chip. You can then test these on another card.

Equally when building out a new card, like you did taking yours from 4MB to 10MB, it's better to add one bank at a time and then test, rather than adding in everything at once. This way you have faulty chips narrowed down to a single set of four.

You can figure out how the banks are arranged by using a multimeter to check the chip select lines. You can remove banks in any order.
 
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TrueNorthStrong

Well-known member
OK, I'll have to look into the chip select lines and better understand that so I know exactly what I'm taking out.
For what it's worth, I didn't use hot air for installing the chips. My usual solder, chip quik flux and drag soldering, with some spot checks as needed. I don't have low temp solder (I really ought to at this point), I'm using 37-63 leaded solder.

I suspect the chip damage to be done to the chips on the edges of the card. When I was doing the work, the connections for the chips and legs on the edge of the card were extremely close to the edge of the board, and they had applied some sort of wax or epoxy there. I assume that was done to stop any shorting that could happen with inner layers bridging to the standard RAM card. They seat right up against each other, edge to edge. I had already soldered the chip on the non-edge side, so I was motivated not (read: too lazy) to remove the chip fully and remove the wax. I just left heat on it until it melted out of the way. Probably not smart, but I wasn't aware how fragile the chips are. Lessons learned!

I'll go remove banks along the edge and see how it goes.

Thank you!
 

croissantking

Well-known member
OK, I'll have to look into the chip select lines and better understand that so I know exactly what I'm taking out.
For what it's worth, I didn't use hot air for installing the chips. My usual solder, chip quik flux and drag soldering, with some spot checks as needed. I don't have low temp solder (I really ought to at this point), I'm using 37-63 leaded solder.

I suspect the chip damage to be done to the chips on the edges of the card. When I was doing the work, the connections for the chips and legs on the edge of the card were extremely close to the edge of the board, and they had applied some sort of wax or epoxy there. I assume that was done to stop any shorting that could happen with inner layers bridging to the standard RAM card. They seat right up against each other, edge to edge. I had already soldered the chip on the non-edge side, so I was motivated not (read: too lazy) to remove the chip fully and remove the wax. I just left heat on it until it melted out of the way. Probably not smart, but I wasn't aware how fragile the chips are. Lessons learned!

I'll go remove banks along the edge and see how it goes.

Thank you!
I found this tech note really helpful for doing RAM related antics on my PB180:


See pages 25 to 31.
 

alectrona6400

Well-known member
if anyone has interest in modding ram cards for the powerbook 500 series... the kta-pb500 cards can be very upgrade-able if you track down the right memory chips and compare how the different variants have their jumper resistors (0 ohms) set. i should probably do more research on these, because if you're madly insane like me you could easily get a 32MB card this way. i upgraded my 8MB one to 16MB and i still have another 16MB worth of room (8 chips) for upgrades, though i have not found the right chips for that just yet.
 
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