IIsi weak sound volume, can anyone here narrow down the caps needing replacement?

[DaiyuHurst]

Hi folks,
I have one complete IIsi and another with a dead PSU, but both exhibiting very weak sound output
(of course, I have to swap in the good PSU for the one). Can anyone here narrow down which caps need replacing?

Dai

 

[finkmac]

have you replaced any of the mainboard caps?

is the "good" power supply recapped?

 

[DaiyuHurst]

have you replaced any of the mainboard caps?

is the "good" power supply recapped?

I doubt any of these bits have had any love - they were eBay purchases. At least they didn't experience battery rot.

I have a third board that's dead as a doornail.

 

[Callan]

All of the electrolytic caps need to be replaced. They're all leaking already. Bet on it. If you haven't capped your power supply you best do that too.
As for your weak sound. Make sure to check your speaker and the leaf springs that connect the speaker to the motherboard (clean them / check tension). Motherboard side - check uk3 and transistors 1a & 2a.

 

[finkmac]

yeah you really shouldn't be turning these on until they've been completely cleaned and recapped.

 

[DaiyuHurst]

All of the electrolytic caps need to be replaced. They're all leaking already. Bet on it. If you haven't capped your power supply you best do that too.
As for your weak sound. Make sure to check your speaker and the leaf springs that connect the speaker to the motherboard (clean them / check tension). Motherboard side - check uk3 and transistors 1a & 2a.

Yeah, the speaker looked ok, and after slightly burnishing the contacts, I treated them with Stabilant 22, but no change.

I can do the axial and radial lead caps, I have enough eyesight to still do that. But the surface mount caps are beyond
my dwindling ability. I'd have to pay someone to do that. Recommendation?

I also planned to try replacing the rectifiers on the PSU, as per this post:

J

Thread 'Troubleshooting a IIsi Sony APS-06 Power supply - blown capacitor caused by bad diodes in series with C105'

Jul 7, 2021

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.

...

• joshc
• Replies: 12
• Forum: Mac II, Quadra & Centris

 

[DaiyuHurst]

yeah you really shouldn't be turning these on until they've been completely cleaned and recapped.

And wow, the two boards are working fine. Number three, ugh.