techknight
Well-known member
if you have no TERMPOWER, that means your fuse or inductor feeding the SCSI bus and/or IC is open circuit. Testing and replacement will bring the bus alive.
Mac SE/30 SCSI problem
- Thread starter TjLaZer
- Start date
pbMacGeek17
Member
TERMPWR checks out good (+5V) on both the internal and external SCSI connectors. I actually checked it at each of the inductors first and finally at the connectors themselves. I can't verify power at the IC due to the short cable connecting the logic board to the computer, but I'm beginning to suspect the problem is the hard drive. I plan to buy an internal SCSI terminator to install on the logic board to see if that cures the problem. I have an external Zip SCSI drive that I can test the bus with once I can terminate the internal bus. Anyone have a better suggestion or alternate path I should be investigating?
pbMacGeek17
Member
My SE/30 SCSi problem has been fixed!! The via connecting pin 25 of the SCSI chip to pin 9 of the SWIM chip was corroded by leaked capacitor fluids and was no longer conducting. I formed a solder bridge over the top of it after exposing the surfaces of the connecting traces and Voila! the system booted off the hard drive like a champ. This repair also fixed the sound problem I was having (low volume and truncated startup sound). Thanks for all the advice and help provided by group members.
In diagnosing this problem, I creatged an expanded version of a previously submitted schematic of the SCSI pin connections. This expanded scshematic depicts each of the chips that connects to the SCSI chip (with their respective pinouts) in the same orientation as they are mounted on the MOBO. This allowed me to rapidly check continuity paths for each of the SCSI pins to identify the path that was broken (open circuit). If anyone would like a copy let me know and I'll forward a JPEG image.
In diagnosing this problem, I creatged an expanded version of a previously submitted schematic of the SCSI pin connections. This expanded scshematic depicts each of the chips that connects to the SCSI chip (with their respective pinouts) in the same orientation as they are mounted on the MOBO. This allowed me to rapidly check continuity paths for each of the SCSI pins to identify the path that was broken (open circuit). If anyone would like a copy let me know and I'll forward a JPEG image.
Blinkenlightz
Well-known member
I'd love a copy of your diagram if you still have it!
ants
Well-known member
Hi all, not sure if anyone is still following this thread but I'm hoping for some advice.
I have an SE/30 motherboard with dead SCSI (both internal and external). I've checked for continuity between all of the pins in the IDC header and the 53C80E SCSI chip - they are all good.
I've also checked the TERMPOWER and it's measuring 4.75 volts - is this within an acceptable range? If not, how could I get it to 5v?
Failing that, I guess the SCSI chip itself could be dead? I think replacing it is beyond me.
But also reading the post above by @pbMacGeek17 he mentions broken traces to the SWIM chip - which chip is this on the motherboard?? Then I could test it.
Hope someone can help?! Thanks.
I have an SE/30 motherboard with dead SCSI (both internal and external). I've checked for continuity between all of the pins in the IDC header and the 53C80E SCSI chip - they are all good.
I've also checked the TERMPOWER and it's measuring 4.75 volts - is this within an acceptable range? If not, how could I get it to 5v?
Failing that, I guess the SCSI chip itself could be dead? I think replacing it is beyond me.
But also reading the post above by @pbMacGeek17 he mentions broken traces to the SWIM chip - which chip is this on the motherboard?? Then I could test it.
Hope someone can help?! Thanks.
Bolle
Well-known member
4.75V is perfectly fine.
Get your hands on the schematics and measure all other signals going to the SCSI chip:
-data and address lines between CPU, PDS or ROM SIMM and SCSI chip
-chip select, DACK and read/write signal lines between GLU and SCSI chip
-IRQ and DRQ between VIA2 and SCSI chip
One of them is probably bad.
Does your board boot fine from floppy?
Get your hands on the schematics and measure all other signals going to the SCSI chip:
-data and address lines between CPU, PDS or ROM SIMM and SCSI chip
-chip select, DACK and read/write signal lines between GLU and SCSI chip
-IRQ and DRQ between VIA2 and SCSI chip
One of them is probably bad.
Does your board boot fine from floppy?
Crutch
Well-known member
Seconding what Bolle said, I had a similar problem last year ... it was fairly easy using the schematics to just check continuity from every pin on the SCSI chip to wherever it was supposed to be going using a meter. In my case, the board had signs of cap damage near the SCSI chip and although all the vias looked OK visually, it turned out one of them wasn’t conducting to the back of the board. I was able to solve the problem by soldering a jumper in place to make an end-run around the bad via.
The schematics are here https://museo.freaknet.org/gallery/apple/stuff/mac/andreas.kann/schemat.html
The schematics are here https://museo.freaknet.org/gallery/apple/stuff/mac/andreas.kann/schemat.html
Last edited by a moderator:
ants
Well-known member
I FIXED IT!!! THANK YOU @Bolle!
I started checking each connection, and I re-checked them on a known working board to ensure I was doing it correctly. I eventually found IOW on the SCSI chip was not connecting with the GLU chip, but it was connecting fine on my working board.
I soldered a wire between the two chips, and then after fixing the two pins I accidentally soldered together
I booted it up and the Mac finally recognised the hard drive.I'm delighted - that's by far the most technical thing I've done with my Mac hardware. Cheers
I used electrolytic capacitors on this board because they are easy for a beginner like me to solder, and I can get them from my local electronics store just down the road. The legs on these ones are so wonky from me repeatedly bending them out of the way to get to the SCSI chip!
