HELP!!!! TRS-80 Mod III M/B NEEDED!!!!

From: Jason Willgruber <>
Date: Mon Dec 28 18:07:22 1998

>Most likely you either shorted the mains side of the PSU to something on
>the secondary side, or you messed up the regulation circuitry, probably
>the former. The damage sounds like what you'd expect with 110V on a board
>of TTL...
>Ouch!. It's even possible that you've blown chips in the printer....
The one paper clip fell across the little clip that supplies 110v to the
main PSU. That's what blew the breaker. I tested the printer on my Tandy
1000, and it still works.

>There are 2 power supplies in the Model 3 - one on the side of the drive
>tower, one on the front of the logic cage. Which one got zapped ? The one
>on the drive tower supplies the drives and the FDC board, the one on the
>logic cage supplies the CPU board, RS232 board and video board.
Neither. The main M/B got zapped. I can power it up w/o MB in it, the
video lights up, and the drives go for about 1 second on power on.

>You might also be looking for a second PSU and drives :-(. This is a
>machine to rebuild slowly - get working PSUs (and test them on dummy
>load), then add just the CPU board and video and check that it goes into
>ROM basic correctly. Then add the floppy controller and drives. Finally
>add the RS232 board.
>I've fixed model3's and 4's, but never one that this has happened to.
Everything's fine but the CPU board and RS-232 card.

>A couple of other suggestions. A model 4 CPU board (non-gate array only?)
>will drop in there, and will run all model 3 software. So that's
>something to look for. The other possibility is to find a cassette-only
>model 3 or model 4 and move your (working) FDC, tower, drives and second
>PSU into in.
I was thinking about that, but won't I need a new keyboard, too? I really
don't want to do that, because I just rebuilt every switch (they're not the
rubber cup type) a few months ago.

>The upgrade is (IIRC) just adding columns of 4116 chips. Worth bring it
>up to 48K anyway when you have the case apart.
Well, the RAM banks on the fried board were all full, so I guess it had 48k.
                 -Jason Willgruber
                  ICQ#: 1730318
Received on Mon Dec 28 1998 - 18:07:22 GMT

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