I purchased a TRS-80 Model 3 with multiple issues as stated in my original post. This issue is for a burnt trace on the PSU that was powering the main board. I'm currently using the PSU that powered the two internal disk drives as my main board PSU--I assume the PSUs are interchangeable. Looking for advice on how to fix the broken trace. Can I just solder a trace, or do I need to bridge the break by soldering a short jumper wire? Looking at the components, I don't see any physical issues--especially around the broken trace (D2 - diode). Has anyone come across a burnt trace like this or would there be a likely (or known/common) cause...e.g. a failed capacitor, resistor, etc. Thanks.
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Burnt trace on PSU for TRS-80 Model 3
- Thread starter gerha7
- Start date
Chuck(G)
25k Member
First thing is to isolate the fault--why did the trace burn? Typical PCB trace can handle several amperes before becoming charcoal. Repair with wire after that is perfectly okay.
daver2
10k Member
Are you sure the two power supply units are compatible with each other? You use the word "assume".
If they are not the same (for some reason) then you may have caused the failure.
Yes, you need to find the fault before repairing the vaporised piece of PCB track. Otherwise, if it is still present, something else will go.
Solder us only really a conductive adhesive. You need to repair the break with a piece of wire. You will also need to carefully scrape some of the protective coating off the remaining PCB tracks to get a good solder adhesion, and then apply some paint or varnish once repaired to return the protection.
Dave
If they are not the same (for some reason) then you may have caused the failure.
Yes, you need to find the fault before repairing the vaporised piece of PCB track. Otherwise, if it is still present, something else will go.
Solder us only really a conductive adhesive. You need to repair the break with a piece of wire. You will also need to carefully scrape some of the protective coating off the remaining PCB tracks to get a good solder adhesion, and then apply some paint or varnish once repaired to return the protection.
Dave
daver2, the trace was burnt when I got the machine, before I even turned it on. It had a lot of mice damage--even the power cord was chewed so I wasn't even going to plug it in. I took it apart to assess the damage and that's when I found the trace (among many other issues).
daver2
10k Member
Ah, the dreaded mice...
Dave
Dave
mark0x01
Experienced Member
Other than component failure, another possibility is a stray screw shorted it out to the chassis.
It looks to be in the rectified mains DC feed heading to the switching transformer.
It looks to be in the rectified mains DC feed heading to the switching transformer.
Jay Newirth
Experienced Member
Why not consider a new modern power supply replacement for the Model 3? I sell them at https://jaynewirth.wixsite.com/newsoft (also sell a version for the Model 4/4D and 4P)
Hi Jay, yeah I think that's what I may have to do. Even though I could repair it, I still got a 40 year old PSU. Plus, I don't know where it's been, i.e. I bought the Model 3 on eBay so it could have been stored in a shed in the heat & cold for years--who knows.
I assume the two PSU's that come with a Model 3 with two floppy drives, are identical PSU's?
I assume the two PSU's that come with a Model 3 with two floppy drives, are identical PSU's?