On 06/08/18 18:37, Adrian wrote:
Got to kick this habit! I won a 1502 TDR machine for really not a lot of $.
There's little point in fighting the inevitable. I have an inordinate fondness for 1502s - except for the PSU/ battery charger :(
I found another (different) dead transistor in the primary side of the LV PSU and that is now running again but although that may just have been a latent fault from whatever befell the poor thing in a previous life I want to check it a bit before firing up again.
Capacitors are an obvious problem. The axial tants on the PSU are OK until they aren't - I've had a couple emit sulphuric acid (on the 25V rails, IIRC - but see an earlier message of mine.
So the question: Although chassis, battery minus and 0V are electrically the same a lot of thought seems to have gone into the internal grounding/power returns of the various boards in this instrument, I presume to avoid ground loops and things, some boards don't have a '0V' wire back to the PSU but do have a chassis connection for instance and others the reverse. Given the history and crispy -ve wire evidence I want to check I am not sharing amps down returns I shouldn't and I see a large solder tag screwed to the top chassis cross-bar that has had a wire cut from it (next to a warning about the LV PSU board having 165V on it - and it has too, trust me!) but I can't see any wires floating in the breeze, does anybody who has one of these instruments know what should be connected at that
point?
If you mean right by the three coloured connectors mounted on the rear of the PSU board, then there should be a 1cm bare single core wire from the chassis' tag to the 0V PCB trace on those connectors.
