Megger bm10 help - Page 1
Forum section: electronics / repair

author: algorithm
author_rank: Regular Contributor
timestamp: December 10, 2023, 01:17:49 pm
content: Been trying to repair this for a few days and feeling like a failure.Testing the battery, the meter needle goes up to 100. (Much lower than the battery line on the meter)Any other mode doesnt work. Visually no damaged or blown parts.I really dont mind if the voltmeter or ohms mode dont work.But I would like to at least get the insulation test modes working.https://elektrotanya.com/megger_bm10_insulation_tester_instruction_manual.pdf/download.htmlInside theres 2 boards, which appear to be of beautiful quality.2nd board has a transformer with taps for 50v-1000v, 2nd board has a pcb link to 1st board, as well as jumper wires.1st board has 3 switches wired to all those jumpers, as well as + output banana jack socket and - output socket. middle switch directly connects to the needle meter.I guess the rotary mode switch determines how many of those wires get output from the transformer.To make things harder I cant test it with power, putting a dmm on the circuit on 4 c cells either gets no reading or erroneous readings it seems.If I put the com of the dmm on what I understand to be ground I get nothing, if I put com on -ve I see voltage on parts but it abruptly shows the full 6v, even on the - of caps, or diodes, I guess since the circuit is floating is why my tests are messed up?Strangely theres a test pin right beside + input and transformer but I dont know how im expected to use it.Since the boards are layered it makes testing some things difficult. But I fully disassembled both boards yesterday and couldnt find anything to blame.1 of the most confusing parts of testing involved those jumper wires to pins on the 1st board. Namely because 1 of the 1st boards posts is named "14". It has wire "11" going to it. The schematic doesnt show 14. Wire "10" goes directly to 1 of the 3 test switches. As does wire 12. All that seemed okay but pin 14 made me spend hours trying to find it in the schematic.Theres an old ashcroft cap 0.047 1250v, 4 phillips electrolytics, 330uf, 100uf and 2 47uf 10v. The phillips had good esr and testing capacitance in circuit seemed like they were in parallel.Tested all the diodes I saw, took out tr1 but it was good out of circuit.There is an orange drop cap but im uncertain if its worth inspecting. Testing it in circuit it did seem to be 0.100uf over its rating but I still was doubting its why.Every resistor tested good that I tried.If anybody has any ideas for me to try id be happy to. Thanks in advance if you have suggestions or advice.Especially how to test with voltage.

author: algorithm
author_rank: Regular Contributor
timestamp: January 04, 2024, 05:05:13 pm
content: I got this working. Not that anybody seems to care. I replaced the electrolytics and that fixed it.Strange that the in circuit tests made the caps seem good but after I removed them they were all bad on esr and capacitance.But yeah the measurements in all modes work now.Its a huge annoyance to work on this, to work on the base board requires disconnecting the needle gauge wires in order to lift it out to be able to flip it.But the quality of the boards for the time is beautiful.Made in england ! How often can you say something made in england is proper? If I recall theres a "thorn" logo on the rear. As in "thorn emi". 198£ back in 82.Mine had been calibrated at some point (presumably in the 90s) and about half of the wires disconnects were broken off with wires soldered to the post. So that made it more tedious. If separating the top board was possible would have made working on it easier.But the test button interconnections are quite complex. Having to replace the 3 buttons that the external button actuate would be rough.Anyway if you are confused like me about the absence of 14 in the schematic its not a concern.And if your battery test needle only goes up to 100 try replacing the 4 electrolytics.

author: johnrobjr
author_rank: Newbie
timestamp: April 14, 2025, 12:13:22 am
content: Hi:I have one, I want to open up.How did you open it up to revel the PCB.I know how to take the back off, to revel the batteries.But, I don't see any... obvious...screws to remove there.It seems they may be under the front panel plate?Shame to remove it, and perhaps bend it.Regards.