Amiga 3000T Power Supply

[madgrizzle]

Will an Amiga 3000T power supply "turn on" from the switch if the motherboard power cable is disconnected?

NM:  It does when it feels like it apparently.  I think this one is bad.  -9V on -12V rail.. when it feels like working.

I ordered an adapter from http://www.ianstedman.co.uk.  The 3000T case is missing the front, top and left side panels so I don't know if it makes sense to continue to use it (I doubt I will find these parts).  I'm think I will have to move it to a different case, unfortunately.  Has anyone had experience doing this?

[dannyp1]

How are you not missing the right side cover? The cover for the computer covers the front, top, and both sides.

[madgrizzle]

For the 3000T, they are individual panels (left, right, top, front).  The previous owner could not locate any of the panels and has moved.  No luck finding them for certain.

[Castellen]

Will an Amiga 3000T power supply "turn on" from the switch if the motherboard power cable is disconnected?

NM:  It does when it feels like it apparently.  I think this one is bad.  -9V on -12V rail.. when it feels like working.

Yes, without the main board connected the fan should run normally, and you should measure close to 5V on the 5V output.

Without a bit of load on the 5V side, don't pay too much attention to the regulation on the +12V and -12V outputs.

Was working on one of these PSUs the other day which was working normally aside from after an off/on cycle, the PG (power good) output would stay low (inactive), despite all the DC rails measuring as expected.  Meaning the computer would stay in reset state, because _FAIL is permanently low.  Since the supply contains a few proprietary parts with no information, it wasn't an easy fix.  So simply removed the PG output to the main board, and implemented a 5V watchdog the same as what's used in the A3000D.  Not too difficult and it worked fine.

[madgrizzle]

Thanks for the info.  Sometimes trying to power it on results in nothing out of the PSU and when it does seem to want to work, the 5V is 5V.  But then it just stops after a while and there's no power coming out.  I don't think that's normal

[Castellen]

But then it just stops after a while and there's no power coming out.  I don't think that's normal

No, that's not normal.  When it does power up, does the A3000T run normally?

Have a check of the components on the PCB just in front of the fan.  As I recall, there's a couple of 5W 33k resistors with sleeving over them, and an optocoupler with a diode across the LED side.  At least in the 230V version.  I've seen it before where these components can get corroded and cause problems, especially the diode.  It's nothing special, probably just a 1N4148 small signal diode or similar.  If it appears rusted/corroded then you can safely replace it with a 1N4001 or whatever standard silicon diode you've got on hand.

And as much as I cringe when someone suggests electrolytic capacitor replacement as a sure fix for every problem imaginable, it might actually help in this case.

[madgrizzle]

When it powers up, it will run for a few seconds and then just die.. long enough to get green and yellow screens.  Now, it's just not doing anything.

Thanks.  I opened up the case earlier and everything surprisingly looked rather clean.. I was expecting a mess but there was just some dust on the transformer.. One of the pieces that's mounted to a plastic standoff was misaligned (one of the standoff's didn't go through the hole of the piece).  I fixed that, but didn't see anything else glaringly wrong.  I'll open her back up and take another look.  Thanks for the advice.

[dannyp1]

I was having similar problems with my 3000T several years ago. I ended up taking the power supply to a repair shop and having it fixed which cost quite a bit because of the $60 charge just to get it on the bench. I also ordered a new one from Germany which didn't really cost much more than getting the original repaired. I had to convert the German one down from 240 volts to 120. As I recall it was an easy fix. It may have been Versalia I bought it from.

[Kawazu]

When you say that the amiga just dies, does the fan on psu still spin and does it output power and the lights are on or is it completely dead?

[madgrizzle]

When I turned on the computer for the first time, it was working and I had green/yellow screens.  I plugged in a hard drive to the scsi cable (to terminate it) and when I turned it on, the scsi drive made a rather disturbing sound.. like it was trying to spin up.. and then the computer shut down (lights off, fan off, switch still on).

Last night, I couldn't get the fan to spin on it.  I let it set all night and just a few minutes ago I plugged it in and the fan came on.  It's disconnected from the motherboard which I assume drives the lights because there's no light on the panel.

Got it back running and let it run for bit.  I turned it off to try reseating the 3640 but now it won't turn on (fan won't spin).

Also, cap lock doesn't work on the keyboard.. I assume a 3000T is like the 3000.  Maybe CIA (I think that's the chip) needs reseating?

[Kawazu]

If i where you i would try to find a modern PSU with all the correct negative rails and just replace the whole inside.
I had to do that with my PSU, did not get a tick signal so i just gutted the whole thing and i now got a 400w psu inside the original psu case and works like a charm

Just remember to messure the power output before and after so you have connected all the wires correctly

[madgrizzle]

If i where you i would try to find a modern PSU

I ordered an ATX adapter from http://www.ianstedman.co.uk/Amiga/designs/Amiga_ATX_Adaptor/amiga_atx_adaptor.html

It's supposed to provide -5V, tick and fail.. So I think I'll be good using it.  Maybe I'll gut out the original PSU case and shove the new one into it.. so I looks authentic