joshc
Well-known member
This post is a recreation of a previous troubleshooting thread (lost in the recent forum crash) where I had some problems identifying the cause of a blown capacitor in a recapped Sony APS-06 from a Macintosh IIsi.
The exact PSU in question:
I used the correct value capacitor and it was placed in the correct orientation, this is after removal, C105:
C105 is in series with D105 ...
I removed D105, and low and behold, bad diode:
Hiding underneath a heatsink, there's another diode which is in the same series - D106. This was also bad.
After some digging around and help from other members, we managed to find the schematics for this PSU, which are included with the IIsi schematics from Bomarc:
This was the relevant bit of the schematics:
Unhelpfuly, 22UA did not really identify exactly what kind of diode these were - I couldn't find anything online, and it seemed like these were old parts no longer made with that specific part number.
But it was really @techknight who was able to make the most sense of what was going on, I've pulled what he said out of the Google cache from the lost thread:
At his suggestion, I replaced the two bad diodes with 1N4007s or similar - what I actually found to be closest to the spec needed was:
Vishay 400V 1A, Diode, 2-Pin DO-204AL 1N4004-E3/54
so I ordered some of those, put them in, and low and behold - it worked!
I hope this thread proves useful for someone else diagnosing/troubleshooting this particular PSU. When I had the problem, I couldn't find anyone online who had the same issue. Most problems with the IIsi PSU relate to either just the radial capacitors, the SMD caps on the soft power daughter board, or a problem with TH101.
The exact PSU in question:
I used the correct value capacitor and it was placed in the correct orientation, this is after removal, C105:
C105 is in series with D105 ...
I removed D105, and low and behold, bad diode:
Hiding underneath a heatsink, there's another diode which is in the same series - D106. This was also bad.
After some digging around and help from other members, we managed to find the schematics for this PSU, which are included with the IIsi schematics from Bomarc:
Macintosh 68k Schematics : Bomarc Services : Free Download, Borrow, and Streaming : Internet Archive
Macintosh 68k Schematics========================Bomarc Services reverse engineered several Apple Macintosh computers in the1990s and sold the schematics to...
archive.org
This was the relevant bit of the schematics:
Unhelpfuly, 22UA did not really identify exactly what kind of diode these were - I couldn't find anything online, and it seemed like these were old parts no longer made with that specific part number.
But it was really @techknight who was able to make the most sense of what was going on, I've pulled what he said out of the Google cache from the lost thread:
At his suggestion, I replaced the two bad diodes with 1N4007s or similar - what I actually found to be closest to the spec needed was:
Vishay 400V 1A, Diode, 2-Pin DO-204AL 1N4004-E3/54
so I ordered some of those, put them in, and low and behold - it worked!
I hope this thread proves useful for someone else diagnosing/troubleshooting this particular PSU. When I had the problem, I couldn't find anyone online who had the same issue. Most problems with the IIsi PSU relate to either just the radial capacitors, the SMD caps on the soft power daughter board, or a problem with TH101.
. The logic for most Mac PSUs is the opposite to ATX; for ATX power supplies you need to ground the soft power, but for most Mac power supplies (including, I think the IIsi), you need to take the soft power pin high, to the standby/trickle 5 V rail. You might want to try that.