Hello!
I'm currently working on repairing my non-backlit Mac Portable. It was sloppily recapped by the seller and sold as non-working. I've desoldered all smd caps once again, desoldered hybrid, cleaned everything with special cleanser, found some broken VIAs, tracer, restored everything. Hybrid looked great, so after soldering it back I found all the proper voltages generating as it should. Unfortunately, only lines together with mess were on the screen.
After some digging, I've found two suspicious points: /AS signal Vpp was only about 2V, the second problem was that upper half of data bus shows signs of multiple driving. I digged that VIA_EN is always high, together with RAM_OE and 245EN. So this is clear something in chip enable generating logic is messed up.
After cutting some traces I found that this is SWIM pulling down AS line. After cutting this trace going to SWIM, Mac started successfully. It is interesting, that it also tries to boot from diskette (unfortunately right now I only have amiga-formatted ones so cannot fully check it). It moves the head, switches RPMs of FDD. Unfortunately it cannot eject, but that's the other problem.
I'm not sure whether SWIM will work without /AS line. I suspect not. Trying to find the chip (CMOS one) seemed impossible, only to get some powerbook donor board. I've just ordered one. But when studying some info, I've found some information that Powerbook 150 also uses SWIM chip, but its marking is 323-1025-3.
I have a question: did someone try to use this chip from Powerbook 150 in Mac Portable or SE/30 as a possible replacement? I thought this could be SWIM2 chip, but table on bitsavers shows this is SWIM...
I'll appreciate any info on this topic.
Thanks,
Alexander
I'm currently working on repairing my non-backlit Mac Portable. It was sloppily recapped by the seller and sold as non-working. I've desoldered all smd caps once again, desoldered hybrid, cleaned everything with special cleanser, found some broken VIAs, tracer, restored everything. Hybrid looked great, so after soldering it back I found all the proper voltages generating as it should. Unfortunately, only lines together with mess were on the screen.
After some digging, I've found two suspicious points: /AS signal Vpp was only about 2V, the second problem was that upper half of data bus shows signs of multiple driving. I digged that VIA_EN is always high, together with RAM_OE and 245EN. So this is clear something in chip enable generating logic is messed up.
After cutting some traces I found that this is SWIM pulling down AS line. After cutting this trace going to SWIM, Mac started successfully. It is interesting, that it also tries to boot from diskette (unfortunately right now I only have amiga-formatted ones so cannot fully check it). It moves the head, switches RPMs of FDD. Unfortunately it cannot eject, but that's the other problem.
I'm not sure whether SWIM will work without /AS line. I suspect not. Trying to find the chip (CMOS one) seemed impossible, only to get some powerbook donor board. I've just ordered one. But when studying some info, I've found some information that Powerbook 150 also uses SWIM chip, but its marking is 323-1025-3.
I have a question: did someone try to use this chip from Powerbook 150 in Mac Portable or SE/30 as a possible replacement? I thought this could be SWIM2 chip, but table on bitsavers shows this is SWIM...
I'll appreciate any info on this topic.
Thanks,
Alexander
