IIsi works, then doesn't

[pcamen]

I combined two IIsi's today to get one working unit.  One has (presumably) a bad motherboard.  The other a bad floppy and power supply (the system shut off just when the hard drive started to spin).

It worked well, and then I turned it off, took the riser + video card out, removed the memory, and put in higher capacity SIMMs. 

Now, I get nothing.  When I plug in the power cord (yes I did all the above separated from power) I get zip.  No sounds, lights or anything.  Acts like it is not connected to power.

Anyone have a guess?

 

[pcamen]

I should say, this also happened with a LC 475 I had.   I got it and it wouldn't power on at all.  At some later time, I plugged it in and it booted fine. 

Really curious what causes this. 

 

[Compgeke]

Power supply caps in these systems (both 475 and IIsi) are known to fail. Sometimes they work after sitting, sometimes they work after a few times, sometimes they work with some heatgun action on the caps, sometimes they don't work at all. In some like the 475 (and LCs) you can often hear the power supply ticking as the thing tries to start and fails over and over again.

 

[pcamen]

I guess this might have to be my first recap project. 

https://www.bigmessowires.com/2016/04/21/capacitor-replacement-in-a-vintage-power-supply/

I'm going to go with the three capacitor recommendation he mentions:

https://web.archive.org/web/20161028131604/https://68kmla.org/forums/index.php?/topic/19148-iisi-sony-psu-trickle-current-startup/

But, small problems.  That above page (original link https://68kmla.org/forums/index.php?/topic/19148-iisi-sony-psu-trickle-current-startup/ ) doesn't have the second page.

What happened to these pre-site update link that have since gone bad?  Are they still accessible?

 

[AlpineRaven]

Sounds like the PSU has done it - its not a easy one to re-cap the PSU - also its a common issue.

IIsi needs recapping anyway. Ive just recapped 2x IIsi's to 100% recapped, works really well.

Cheers

AP

 

[Elfen]

The LC475 PSU is easier to fix/recap than the IIsi. But it sounds like you need to recap the motherboards as well on both. You just need to get the information to do the information.

IIsi PSU info: http://maccaps.com/MacCaps/Capacitor_Reference/Entries/1990/10/5_Macintosh_IIsi_Sony_Power_Supply.html

LC475 PSU if it is an Aztec unit: http://maccaps.com/MacCaps/Capacitor_Reference/Entries/1990/10/15_LC_I%2C_II%2C_III_Power_Supplies.html

You would need to scour the web for THAT other LC PSU used on the LCIII and LC475

After you recap the PSUs, you should start on recapping the Logic boards.