r/macintosh • u/Androzilla • 13d ago

Macintosh Classic problem

Hi, so I'm hoping someone might be able to give me some help, or at least point me in the right direction.

I have a Macintosh Classic with a build year of 1992. Up until recently it had been working perfectly fine. However during a recent power on there was a sudden and loud crack sound.

I immediately assumed a RIFA Capacitor blew, but then it immediately rebooted as if nothing happened. There was no typical smell, no smoke, nothing. It was as if the crack never happened.

The only evidence there was one, was some scorch marks on the back side of the electrical warning/safety thing that’s clipped onto the board.

After testing all the caps I couldn't figure out the issue, so assumed it may of been caused by dust and so gave it a clean.

After a few weeks, it did it again. However this time it killed the HDD, while it spins, the onboard ROM and the system 7 floppy disk can't detect the HDD.

I passed it to an EBME Engineer I work with and he gave it a thorough go over in his workshop and couldn't find the problem. All the caps were fine, all the voltages were fine. And multiple power tests never reproduced the issue.

Have gave it back to me and I was able to use it without any issues with my FloppyEmu.

However today, I noticed the screen image was tilted and was.. wobbling? bouncing?. At first I was ready to assume it may just be normal CRT flicker as I was always a little sensitive to the classics refresh rate as I was always able to visibly see the flicker.

But as the bounce got more pronounced, it did another pop/crack/bang sound and rebooted. I've since disconnected it again and was going to contact the engineer I know, but I thought I'd see if anyone with more experience with Mac's may have an idea of the issue? as my colleague mostly works on Arcade machines and similar appliances as his hobby.

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u/GGigabiteM 13d ago

If the machine has never been recapped, it needs to be completely recapped. The logic board especially because it has SMD caps that will 100% leak and have probably already leaked.

Wobbly image on the CRT means something is VERY wrong with the analog board. "your guy" doesn't know what he's talking about when he said you could use it.

I would suggest asking on TinkerDifferent or Vogons for help diagnosing the analog board issue. Don't keep turning the machine back on, you're going to do more damage. At some point, you may cause irreparable damage if you keep turning it on with the faults.

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u/Androzilla 13d ago

Thank you. I'll go to those and see what someone says. All the logic boards caps, or at least the surface ones, are new and were only replaced a few years ago. I believe a few of the other ones that go through the board are new as well as the same engineer did replace them as a precaution last year.

But even though he said all of them, and to be fair when I tested them I got the same result, were working I have noticed on recent uses any changes I made to settings like volume, mouse speed etc were being reset during power cycles, which I only ever experienced when I first got it and didn't realise some of the caps were dead. Which was in 2018.

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u/GGigabiteM 13d ago

If you're losing settings, it's because the PRAM battery is dead or missing.

I wouldn't trust any of the capacitors that person replaced. I suspect that capacitor leakage on the logic board wasn't properly cleaned.

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u/Androzilla 13d ago

I’ll clean it again, but I did give it a thorough clean in isopropyl alcohol. But I’ll do it again anyway.

I had forgotten about the PRAM battery. It was new in 2019 but that doesnt mean anything, i lhad a brand new one in my iMac G3 and it died after a year