Amiga 600 Power Issue - Help required.

[slimf]

Hi Everyone..

Just hoping for a little help..

I have been  recapping some Amiga's and one of my Amiga's has a power issue. The  miggy wasn't working when I got it so Ive done a bit of digging.

The Amiga 600 is a REV 1.5 - and the circuit diagram attached with voltages is taken from the 1.5 circuit diagram.

This is with a KNOWN good Power supply.

The voltages are all over the place.

Ive checked the inductors - they are all 1.2ohms which seems about right.

Any clues? This board has been recapped - However it made no difference to this power problem.

I  have removed a few of the caps on the under side of the board (C800)  and it tested fine. The others would appear to be OK, but if I had more  of a clue as to the problem I could remove the others and test out of  circuit.

Any help appreciated.

[rkidd7952]

The measurements show 24v between the +/- 12v rails, just shifted.  I suspect a floating ground.  Are all of the measurements relative to a single ground point?

I'd check continuity of the power and ground traces back to the power jack and check the jack itself for a good connection to the PSU.

Robert

[slimf]

Thanks for the tip Robert.. Your clue about floating ground helped a lot.

I did a check over the board - Its solid as. So I got stuck in with the multimeter.. Seems there was a break somwhere between the ground pin on the power socket and the inductor. Causing the floating ground.

I was able to rectify by putting a temporary jumper (see pic)

The trace that connects these two points is short, and on the top side of the board and is almost 100% covered by the inductor and the power socket.

After putting the temporary wire in place, the miggy fired up - probably for the first time in 18 years.

:-)

Now I just need to decide how to fix permanently - Either find some fine wire and replace the temporary wire or to desolder both the power socket and inductor in an attempt to find the break.

Advice?

[rkidd7952]

You're welcome, glad to hear you got it running!

I'd guess the break is on the power socket side.  It's more exposed and could be damaged if someone yanked the cord.  Does the socket feel loose at all?

I would try reflowing the solder joints that connect the power socket to the motherboard and see if it's just a bad joint.

If it's not a bad joint, the jumper you installed seems like a good approach.  Make sure the "ground" side of C800 has continuity to the ground pin and call it good.

Robert

[QuikSanz]

Because the jumper works after the socket, not a socket problem. The break is probably a cold solder or open trace, I would call it fixed if no bad solder is seen.

Chris

[slimf]

I had already resoldered all the joints on the power socket and inductor - So must be broken track under the power socket on top side of board.

Ive replaced the wire jumper with a much smaller guage wire and neatened it all up.. Just put back into the case and booted workbench 3.1.  :-)

Now onto recapping my next Amiga.. At least the rest work.

[AmmoJammo]

I've had a board with a broken via before... (the plating that connects one side of the board to the other)

So everything looked ok, except, there was no connection from one side of the board to the other!