Batteries leaked in Thandar TM351 bench multimeter - Page 1
Forum section: electronics / repair

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 21, 2016, 02:19:53 pm
content: Not too bothered as this only cost me £3, but I just got hold of a Thandar TM351 bench DMM and the batteries have leaked in it. It's a fairly primitive manual range affair but it stacks nicer than the typical handheld DMMs and it's good enough!Bit of a state inside however thanks to storage problems leading to a leaked set of batteries. It does come up and the ADC is working but it's not reading out anything sensible from the dividers. How best to approach this one?My plan is:1. Dismantle.2. Throw the battery tray in the bin and get a new one. Will run it off the bench supply until I'm sure I can fix it.3. Remove all CMOS ICs which are socketed anyway.4. Carefully clean the top and bottom of the board with IPA and a paint brush.5. Clean the chassis out with soapy water.6. Reflow all the solder joints.7. Continuity check all the traces and repair any that are open.Any other things I need to consider?All top side components appear to have missed the alien acid bath.Grim photos:

author: KhronX
author_rank: Frequent Contributor
timestamp: December 21, 2016, 02:36:04 pm
content: On the bright side, the service manual seems to be availablehttp://elektrotanya.com/thandar_tm351_dmm_1981_sm.pdf/download.htmlSeems to include a pretty comprehensive description of the inner workings, which i imagine should be quite helpful

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 21, 2016, 02:45:03 pm
content: Yeah that service manual is the only reason I considered buying it in the first place. Seems to use only standard and easy to obtain parts which is a good thing.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 21, 2016, 04:24:49 pm
content: Well this one is a write off. I cleaned the board with IPA and tried to clean up a few joints. Used chemtronics wick to clean up, then IPA wash, then resolder. But it turns out that the acid has dissolved quite a few traces entirely as well as destroyed all the tinning on about 50% of the component leads. I carefully scraped the solder mask off around the area with the idea of using a bit of kynar to fix broken traces but I gave up when I found the 11th one. I'd be about £20 down in soder-wick by the time I'd fixed this and I'd have to extract and re-tin all the damn components.Have nicked the trimmer caps out of it as they're really good quality ones, some chassis parts to repair another unit and disposed of it. Totally BER.Batteries + naughty_previous_owner = bin.

author: KhronX
author_rank: Frequent Contributor
timestamp: December 21, 2016, 04:27:29 pm
content: That's quite a shame

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 21, 2016, 04:37:50 pm
content: Yep. First thing I've had to chuck in about a decade as well. Such is life.

author: CJay
author_rank: Super Contributor
timestamp: December 21, 2016, 09:01:54 pm
content: I picked up a couple of the older LED versions of this meter from a surplus supplier, meaning to use the cases for 'something' as they'd been sat in the weather for a couple of months that I know of.Took them home, opened them up expecting to find utter destruction but, nothing, once they'd been cleaned up and dried out, they work really nicely for a simple meter, ideal for a visual display of voltage and current from my high current PSU which lives under the desk.One thing to remember though, in common with the Thandar TF600 meter, the power socket is centre negative with no protection (guess how I know there's no protection) so if you do happen on another at some point and decide to run it on a bench supply...

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 22, 2016, 12:43:42 am
content: The centre negative nearly got me on the TF200 counter. I don't have any C cells around so it went on the bench supply. Fortunately there was a big diode across it and my supply was carefully set up in CC mode(also Thandar - PL310 which incidentally I bought another one of today)I'm starting to sound like a Thandar collector now. Alas no; this stuff arrives dead, is resurrected and subsequently pays for the hobby