Well, Fez. I'm not surprised that it's working, but I am surprised with the repair. It's up there with the "intermittent fuse" which I have seen twice. What was bugging me, was the power supply had no evidence of current limiting, yet you were loosing 12V.
I got lucky suggesting freeze spray on the bridge. I could see the point of going further until the supply was fixed. So, the puzzle was is it the supply or something loading the supply. No current limit through me a curve.
I said earlier that adding TVS diodes on the secondary(s) might be a good option. Your call.
I just got a broken Keithley 485 autoranging picoammeter from ebay for like $90.00 USD delivered. I ordered the suspect $0.25 USD part to fix it. One range read zero, All the other's overload. My finger made the digits jiggle in the nA range. So, one part for sure, possibly two. I'll bet if I snip the part, all of the other ranges will work. The front connector was loose which took out a FET,
The current source I need to work on has more issues. Parts in hand. This one supposedly was fixed and broke again, the seller said and he didn't want to deal with anymore.
The voltage source works with the IEEE board disconnected, so there is a direct short.
Either the 160B voltmeter or a Keithley 480 picoammeter needed a converter chip.
I have frequency counter that needs some tact switches replaced - I have them in hand.
I might get more fixed, because I have to dig out the soldering/desoldering station soon.
Then I have some scopes to work on. A Dallas clock chip replacement that also holds calibrations. So, it's remove (no socket), read it, and program it into another chip. Put a LP socket on the board and hope for the best. The floppy drive will get converted to USB. Then there are two battery scopes, the TEK 211 and TEK212. To get both working, I would need a 3D printed part. Taking a course and doing it locally is an option, but first it has to work electrically. One scope needs battery pack holders which act as spacers for the PCB.
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This week, I was tracking down how to make a high temperature insulator for an isolated NC switch on a 1/4" phone jack. I asked a friend, but he wanted to do it. It's his lathe. So, anyway after his failures and my success at home, I can use a plastic thread forming screw in a piece of Macor (Machineable ceramic) or for reduced temperature service (450F), I can tap a piece of PCTFE.
https://en.wikipedia.org/wiki/Polychlorotrifluoroethylene. It has a slight impact load, but I'll try the ceramic first. Titanium washers will reduce the thermal conductivity from the wall to the part itself. Fun little home project.
Now, my wireless mouse died. So, I just ordered USB surge protectors and a replacement on ebay. The receiver side blew in the last one.
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Glad you liked the label maker.