Hi everyone,
I cleaned it, still doesn't work but the shim is not the issue as one could see the above pictures but that lead me to the issue.
At close inspection it doesn't seem that any other component misses the magic smoke, ...
(Attachment Link)
After some fail attempts to source a new board (contacted the distributor (Welectron), they sent me to Brymen, Bryman sent me to eevblog and then was silence) I would like to give it one more try before send it to a better place.
But before going that rabbit hole, I have some questions:
- beside the schematic is there any other documentation to speed up the process?
- does any know if there are internal traces around the affected area?
- some higher resolution photos in the affected area (for a good one )?
- pcb parts placement would be great
Any tip will help.
Thank you.
That is significant damage, and I did something similar to my 121GW as shown back in post 1314 and in another thread at
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1599418/#msg1599418 (and earlier).
In my case I had mistaken measured a high voltage (1200V 25kHz from memory) that burnt my PCB, but after I cleaned the PCB to remove the burnt section it worked fine again. For you to have a similar burnt PCB (although on a different section of the switch) indicates that your 121GW very likely was also exposed to a high voltage to cause the arc over and burnt FR4.
So, the first thing you need to is dig away at that burnt PCB surface a bit, and then wash it with some IPA. The carbonised section is going to be conductive and is likely causing leakage currents between the pads of the rotary switch.
If that doesn't help (or even if it does), then you might want to check the state of the protection components close to the HY3131 chip, e.g. D13, Q1/Q2, and Q3/Q5. If those seem OK (not leaky or shorted) then it is possible that your HY3131 chip is damaged. The parts may not show visible damage, but still be causing your false readings.