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VFD failure mode
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l0rd_hex:
Hello electro-pals,
I am visiting the in-laws and their GE SCB1001MSS01 microwave / oven has some issues with the VFD display. The rest of the oven functions work and I've done some voltage tests on the various circuit boards and connectors. Thankfully, GE (well, LG probably) included some schematics with voltages in an envelope inside the metal shell. The high voltage area on the display board looked OK, there is 50-80 V DC being generated for the VFD. The board itself gets 5V from another power board so I'm thinking the problem might be on the display board but not with the high voltage as the VFD lights up and prints characters but they are sometimes jumbled. The screen doesn't seem to refresh properly either, a character gets written and is briefly visible but doesn't stay on screen. I've taken a video of the screen here: https://drive.google.com/file/d/19Pmr6pW-cfShygAIXzkR9QbIK9W0dZeI/view?usp=drivesdk
I am thinking the shift registers (td62c950rfg) are borked but I didn't see any obvious damage. Picture of the board here: https://drive.google.com/file/d/19_Wc6zzwG3qXSFhNBKhnQCixacqNfwoi/view?usp=sharing
I'm hoping someone has seen this type of failure mode and might know what part of the VFD circuit I should direct my attention to.
Thanks!
jmelson:
I'd strongly suspect tired electrolytic capacitors, first. This board is certainly powered on 24/7, so that could deteriorate them. I see 3 on the display board, but there might be mre on the CPU board.
Jon
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