Amiga psu -29V on -12V

[Lisko]

Hi all, I bought an amiga 600 without power supply so I also grabbed a new meanwell based psu. At start the amiga powered up just fine but after about 15 minutes I inserted a floppy disk and a red guru showed up. I tried to reboot but the amiga hanged up so I switched it off and when I switched the psu on again nothing happened and no sign of life from amiga. I then used a multimeter to check psu pins and I noticed that on the central pin there were -29V instead of -12. Now I don't have another psu ready for testing so I ask you what damages, if any, could be done by this and how to check them. Thank you.

[grond]

I think -12V is only used for the audio circuit.

[MoonDragn]

Originally Posted by Lisko

Hi all, I bought an amiga 600 without power supply so I also grabbed a new meanwell based psu. At start the amiga powered up just fine but after about 15 minutes I inserted a floppy disk and a red guru showed up. I tried to reboot but the amiga hanged up so I switched it off and when I switched the psu on again nothing happened and no sign of life from amiga. I then used a multimeter to check psu pins and I noticed that on the central pin there were -29V instead of -12. Now I don't have another psu ready for testing so I ask you what damages, if any, could be done by this and how to check them. Thank you.

Check the fuses on your motherboard see if they are open. You should smell the familiar smell of burnt electronics if there is anything fried.

That's where I would start.

It looks like the -12v is used in the audio decoupling circuit and the RGB video connector(converted to -5v on pin 21)? I think there is also a decoupling circuit on the floppy that uses that -12v as well.

ps. oh that last part may be the reference voltage for the line driver for the audio circuit (for the LED?), not for the floppy.

Possible chips affected: U15 and U28.

[amigasith]

Hi Lisko,

if you're lucky, nothing bad has happened to your Amiga. I had the exact same thing a couple of years ago. When I switched on my trusty old A500 one day, I only had a white screen. No Kickstart logo, no floppy disk clicking.

I immediately switched it off again and found out that the -12V line was giving me -20V. I opened the PSU, tried to figure out what's going on and actually found the issue: In my PSU, there was a voltage regulator that generated the -12V from a -20V source. And it was this voltage regulator that was simply dead. Replacing it solved the problem.

The good news: My A500 works just fine again since that day. No components were killed

Cheers,
Marc

[Lisko]

Now the machine boots up, time to see if any damages. Thanks