Chauvin Arnoux C.A 6545 5kV Megger

[Mad Axeman]

We've got a Chauvin Arnoux CA 6545 5kV Megohmmeter that's developed a fault. Initial fault was it wouldn't IR at 5kV, zero volts even with probes open circuit. The 500v, 1kV and 2.5kV were fine. It was sent off for repair and we got told it was too old and parts were no longer available. Not being one to throw things away I took a look. Since it came back from repair(!) it had developed 2 more faults. It wouldn't charge (blown fuse on charge board) and all ranges now showed a 'Fuse G' fault. According to the manual this fault refers to the ground terminal fuse. After a bit of checking I found a cracked resistor which I replaced. It now works on 500v & 1kv but shows 'Fuse G' on 2.5kv and 5kv. There's a heat shrinked package (red package in last 2 pictures) connected between 'G' and '+' which contains 5 x 222 6Kv caps wired in parallel and 2 x 10k resistors (1 each side of the caps). I didn't have a capacitance meter with me to check these. Anyone have any experience of these meters and can shed some light on my next move or have a circuit diagram???

[m k]

No experience nor schematics but arcing is clearly an option.
Maybe it has some insulation problems.
If so then possibly not very easy task.

That line of 22ohm resistors, is the last one replaced?

[Mad Axeman]

Yes, the last resistor was found to be broken when it came back from a quote for repair. Was fine when it went! I haven't had a chance to look at the unit since I posted my message but my next plan is to swap out the 5 x 222 caps (in the red heatshrink) between 'G' and '+'. 

[Mad Axeman]

I think I may have got to the bottom of the problem. I swapped out the  5 x capacitors and 2 x resistors and gave it a try. No more 'Fuse G' error message. 2.5kV range now works. 5kV tries but bombs out with a low battery error after trying to ramp up the voltage. Looks like my next job is to source a new battery and try again.

[m k]

So a good guess is that the repair place tried to boost the battery with a charger and burned the fuse.
How they broke the resistor is another thing, maybe all of those old mass resistors are more or less fragile.

[Mad Axeman]

I was thinking of replacing all of those resistors. I had to buy them in a pack of 10 so I've got plenty there.