Well, the TRS-80 didn't power up after my cable work yesterday, so I had a closer look at the PSU, and none of the necessary voltages, so 15-17 VAC and 19-21VDC.
I popped the bottom of the PSU case off, which is held on by 4 screws and found a mass of plastic/cardboard insulation:
And buzzing out the mains input, I found there was no continuity on neutral, so opened the plug up and found the neutral connection had come adrift, so fixed that, but despite that, I still had no power at the lead that plugs into the TRS-80.
At that point I realised I needed to pull the plastic grommets where the cables entered the PSU and they were the horrible hard plastic cable crimpers that do this:
Both the mains lead and power to the TRS80 lead were like this, so they got copped in case 40 years of crimping had damaged them. This is the output lead and you can see that the GND lead has come away. The white lead also came away, more on that in a minute.
Unfortunately, the transformer, with the PCB attached to it is epoxied into the PSU, so I decided to stop and have a cup of tea, stirred with an engineers spoon
The PCB on the top is retained by 2 metal tabs, so bending these out of the way, it was necessary to de-solder the 3 outputs from the transformer and the mains lead to be able to lift the board up and see where the output leads were soldered to:
You can clearly see the remains of the white wire that may have been pulled when I was removing the grommet. The black GND wire appeared to have been poorly soldered in, and was just hanging loose. Having cut the cable previously, I made sure to mark the positions before soldering the lead back to the PCB:
Note that I also had removed the live and neutral from the other side of the board, but it turned out it wasn't necessary. I then put the PCB back in it's original position, folded the tabs back and re-soldered the 3 transformer outputs, and my freshly tinned mains lead:
A quick test and all the voltages were now present at the plug
So I tried the machine and we're off and running again:
It was then just a case of refitting the horrible crimpy grommets as I had no alternatives (Should be good for another 40 years
) and refitting the bottom plate, making sure all the cardboard/plastic insulation was back in it's original spot.