> Thanks Allan for the response. I have the HP-5245L and the HP-5262A Time > Interval Unit, but it is not working. Problems in the PS
One thing you can do is to replace any blown TO-3 pass transistor and associated support circuitry with a TO-3 three-terminal regulator of the appropriate polarity. It is often easier and cheaper than trying to find a NOS transistor or decent equivalent. I did this in my 5246L, and it worked great. The trouble with a bad power supply is that the problem can cascade, especially if the supply doesn't include a crowbar. If the ambient temperature gets too high -- perhaps because the fan seizes (my counter) -- the pass transistor can go into thermal runaway and saturate before giving up its smoke, frying a bunch of things on the associated power rail. Things to look for include: -- bad electrolytics tied to the rail beyond the pass transistor. -- resistors tied to the rail in series with other circuit elements (typically transistor legs). Series resistors offer some protection to the other elements with a runaway supply. Blown resistors are usually plainly evident from inspection. -- transistors legs tied directly to the rail. Carefully check over the schematic for these -- series resistors weren't used with some of the transistors in the sampling circuit of the 5246L: several have their collectors tied directly to -15V. They all fried in my counter. Hope this helps. -ch _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts