11/34a problems continue

I've not even started my normal rant about board-swapping (rather than repair) yet.... Anyway, I do feel that it is somewhat foolish to replace a part -- any part -- withoug a clear idea of what the problem is. You might be looking in totally the wrong area,. or the part might be being damaged by a fault elsewhere... The initial fault, IIRC, was that the lamp on the -15V regulator brick wasn't lit. Now that doesn't even mean that the -15V rail is missing (the lampe might have blown). I can think of many reasons why that lamp might not light, including : The lamp itself has burnt out The -15V rail is missing due to a fault in the reuglator brick The -15V rail is missing due to a shrot-circuit in on of the loads on that rail (e.g. a serial card) The input to the -15V regulator is missing due to a bad connection, open-circuit transformer secondary winding, whatever The +15V supply to the -15V regualtor is missing due to a fault on that regulator board The +15V input is missing due to a bad connection/broken wire between the +15V board and the -15V brick The +15V rail is missng due to a short in one of the loads on that rail (e.g. a serial card) The +15V rail is missing because the input to that regulator is missing (brocken connection, open-circuit transformer secondary, etc) It is pointless, IMHO, to go any further unless you know where to look, and that means doing tests to eliminate some or all of those posibilities. When you know where the fault is (e.g. you know the +15V rail is misisng, you know the inputs to that board are OK, and the load doesn't seem to be a dead short), then you can look at the next level down and find, e.g. an open-circuit power transistor. The best advice I was ever given for faultfinding (and it applies to everything, not just classic computers) was 'Measure, think, then repair'. Make measrurements and gather evidence. Think about what those measurements are telling you (it may then be necessary to make more measurements..). Then, and only them, start replacing components. This may not be the modern way to repair things, but it's not let me down yet (which is more than I can say about some other 'methods'). -tony