I've now completed the replacement of all electrolytics in my IIsi PSU.
Hopefully, this will have corrected the lingering system problem I have had, where the keyboard would start to randomly repeat keys after the IIsi had been connected to power for several hours. Wierdly, this fault would start whether or not the IIsi was powered up all that time. It would self-correct when the power was fully disconnected for a few hours. So the issue, I am guessing, was in a buildup of ESR or loss of capacitance in caps feeding the 5v rail, eventually producing some ripple that disrupted the ADB hub.
As I changed all the caps I found considerable sticky evidence of electrolyte leakage under the caps, especially at the 1200uf and 2200uf secondaries. No corrosion, though.
When I removed the cakes of hotmelt glue that had been slopped around at original assembly, I found a couple of corrections to the table of cap values posted earlier. Here is the corrected table. It does not cover the several tantalum and ceramic caps that I have not seen necessary to replace (so far!)
C101,C102 220uf x 250v
C105 4.7uf x 400v
C106 100uf x 10v
C202,C203 2200uf x 6.3v
C211,212 1200uf x 16v
C302 56uf x 35v
C401 100uf x 25v
C402 47uf x 25v
After seeing how many problems an unreliable PSU can cause, I strongly recommend PSU re-capping as much as logic-board recapping. Don't wait for the smoke.
Rick
Hopefully, this will have corrected the lingering system problem I have had, where the keyboard would start to randomly repeat keys after the IIsi had been connected to power for several hours. Wierdly, this fault would start whether or not the IIsi was powered up all that time. It would self-correct when the power was fully disconnected for a few hours. So the issue, I am guessing, was in a buildup of ESR or loss of capacitance in caps feeding the 5v rail, eventually producing some ripple that disrupted the ADB hub.
As I changed all the caps I found considerable sticky evidence of electrolyte leakage under the caps, especially at the 1200uf and 2200uf secondaries. No corrosion, though.
When I removed the cakes of hotmelt glue that had been slopped around at original assembly, I found a couple of corrections to the table of cap values posted earlier. Here is the corrected table. It does not cover the several tantalum and ceramic caps that I have not seen necessary to replace (so far!)
C101,C102 220uf x 250v
C105 4.7uf x 400v
C106 100uf x 10v
C202,C203 2200uf x 6.3v
C211,212 1200uf x 16v
C302 56uf x 35v
C401 100uf x 25v
C402 47uf x 25v
After seeing how many problems an unreliable PSU can cause, I strongly recommend PSU re-capping as much as logic-board recapping. Don't wait for the smoke.
Rick