I bought a Tandy Portable Disk Drive 2, which is a rebranded Brother drive that has been adapted for use with a TRS-80 Model 100 portable computer. The drive has issues, some of which I have already addressed, but the one that prompts me to post this message has to do with the power supply.

I have determined that the power input is capable of supplying about 6VDC to the board illustrated below when powered by a set of four fresh AA alkalines, and about 7 VDC from a TRS power adapter, aka "wall wart".

With the adapter supplying power and with the cable to the drive PCB disconnected - in other words, with little or no load to drive - I find that the transformer T1 gets very hot; too hot to touch after a minute or two with the power switch (upper left in the overall picture) in the "on" position. The transistor next to the transformer gets hot as well, though not as much as T1. Neither component heats up unless the power switch is "on".

I'm not much of an EE but it seems to me that the likely explanation for this phenomenon is that some other component - maybe a capacitor? - has become a dead short, causing the transformer to run at capacity.
Another possible explanation might be that the two input leads to the board have at some time been switched, causing a reversal of polarity. This occurs to me because for both the batteries and the adapter the red wire shows negative and the dark blue wire shows positive on my meter.

I'm hoping for some guidance from more knowledgeable readers in order to diagnose the problem further.

Thanks for your replies,


PS Closeup.jpg PS Overall.jpg