I have a Fluke 8800A waiting for reanimation (initial symptoms: faint red range LED, no reaction to buttons, former owner broke the the green paddle and put acetone to glue it back managing to melt it on the case
).
Because I was felling in need of (relatively) instant gratification, I've open it, changed the usual basterds (see the picture, trifecta, Sprague, Phillips and and MEPCO, this one on the 5V being actually 16pF !!!) and the old girl sprang to live, the initial readings had some offset but were stable enough, except for the high voltages ranges, where it was a real noise +/- 15%, egal what voltage was applied.
After cleaning all the contacts, carefully marking the position of the trimmer potentiates and exercising them few times, everything stabilized nicely EXCEPT for the bloody zero on short, this was moving in between +70 and+ 20 on the ends of the front panel zero trimmer
, I was preparing to replace the main adjustment resistor, as the manual suggest, realized that I have none
and staring to feel bad, but while moving the device on the table the zero offset I've seen some mechanical variation on the reading with the input shorted.
Long story short, the bloody range relay it's a POS, I've clean it as good as I could, put it back and I've got a minimum value of +14 and stable, exercising it by putting on and off a 150V to switch the relays reduced it to 6 and that was it, no way to go lower, but at least now it's really rock stable, the 10V in the picture are staying like this for 2Hrs and I'll let it run over night, so mission (almost) accomplished
.
Now I have a couple of questions for the Fluke gang:
- Any NOS or other replacement for the ranging relay available somewhere ?
- Anybody in DE/EU has a donor unit and willing to send me the green (or any paddle) to replace the power supply Pfuscherei ?
- Any ideas for the zero adjustment WITHOUT replacing the main calibration resistor if I can't get a new relay ?
Finally after almost 2 1/2h it started to blink 10.0000/9.9999, I'm taking bets for tomorrow for the drift
.
Cheers,
DC1MC
Obligatory pictures attached
.