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Hi @techknight thanks for for your reply, didn’t notice it before... good to know it’s not the mobo, though ai noticed internal SCSI wouldn’t work after my mods only an external scsi Zip drive. Ill try testing the caps before replacing them... btw, do you still have access to the schematics for the iisi psu?

I’ll have to check tomorrow but I don’t think so. Thanks again for your help!

Ok thanks for the tips... I have some ceramic resistors, should I use the highest rated one? I have a very basic multimeter but it should do the job. Back when I opened my 68kmla account it was for a competition and I wanted to overclock the 68030 to 25MHz by changing the Quartz crystal but have had problems ever since (not the psu) despite putting the original crystal back in. Think one of the feet of the crystal is not attached properly and may have affected other components?

Yeah there was a fuse, when it blew that’s all that was left... not sure about C116, I can check my other PSU it’s the same model. I’ll check C302. Thanks for your tips @cruff Edit: just checked C116, nothing meant to be there. Checked both PSUs. Well spotted though! Actually, I’m wondering if it’s the MB that’s causing the problem? Is there any way to test the PSU outside the IIsi case? My electronics knowledge doesn’t extend to PSUs...

Ok attempting to upload some images.... If anyone can spot anything or has any recommendations, I'd appreciate it. Have never repaired a PSU before. But it is discharged I believe... in that it hasn't been connected to power for at least a year. @hackdog @techknight @GeoffreyReed Thanks in advance!

Hi hackdog, thanks for your fast reply! to be honest, I’m not really sure what the problem is... one psu blows fuses straight away and another just clicks and shuts down. i don’t suppose the schematic indicates the ratings of the parts? the only things I tested were the diodes since I guessed that could be one reason the fuses blow so quickly. everything looks pretty clean except I think I recall a bit of blackening around some parts of the circuit board. if I upload some more photos could you take a look? cheers and thank

So I tried to link to my post back in 2018, still haven’t gotten anywhere... @techknight and @hackdog if you have any suggestions would be most appreciated!

Ok so the post I’m referring to is here: The dude with the schematic is @techknight And the repair guy is @hackdog Would be great if either or both of them could chime in. I’ve got two dead IIsi’s and they’re one of my favourite 68k macs!

Thanks guys for your input. Would love to get my hands on a copy of the PSU schematic! I read there was a guy on this forum that had them and was very handy at repairing them too! Will see if I can find his name. i saw a broken IIsi listed for $300 locally but seems a bit high.

Hi, sorry to resurrect an old post but need some help with my IIsi power supply... see here: thanks!

Hi all, been a while since I last posted here, about the same time I tried to use my IIsi(s)... so dug them out but neither of them would power on. I would get a brief click, fan and light then they would power off again. Tried replacing the fuses, which might have done more harm than good since the guy sold me slow fuses by mistake which I stupidly tested anyway. after getting the right fuses they blew straight away. so did some continuity testing and found at least a couple of the zener diodes are allowing current in both directions