Hi!
Can anyone offer me any tips for repairing the 750 VAC Range on my Keithley 2100/Array M3500 4½/5½/6½ digit multimeter please?
There are no p.o.s.t. errors displayed and all the DC and low AC voltage ranges up to 100 VAC range appear to be operational!
When I connect it to mains on "Auto" the meter constantly changes ranges between 100 VAC and 750 VAC every second, displaying only dashes with no numerical readings whatsoever, and on "Manual 750 VAC" it reads "63.899 VAC" (4½ digit setting).
If you then disconnect the mains from the input it stays stuck at "52.4 VAC!"
I first became aware of this fault trying to check the 480 V secondary in a "Mullard High Speed Valve Tester", the meter displayed "131 VAC" which stuck there, and I knew that can't be right because the green spot on the Mullard tester was present, this Keithley meter showed "422 V" on the positive side of the CRT supply and "–525 V" in the negative side of the CRT supply!
The 480 V CRT h.t. secondary is ordinary 50 Hz a c., not a pulse or oscillator type supply!
Rechecking across a convenient valve heater in the Mullard Valve Tester gave me a reading of "6.2532 VAC" on the '2100!
(If there's a way to get rid of all those daft decimal places I haven't found it yet, one or two decimal places is more than enough for me!)
Before anyone asks why I'm using a Lab Quality 6½–digit meter on an old Valve Tester, the answer is all my other test meters need repairs, and the Black Star 3225MP that (did!!) once work has now got ink leaking all over the LCD so that's a goner as well !
Chris Williams