Bad after each power reset, possible display board problem?

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Joined: Sun Jan 26, 2020 6:32 pm

Bad after each power reset, possible display board problem?

Post by bsd01 »

Hi, I have a strange issue that started happening for no reason(I never overloaded inputs or power).
What happen is that each time I turn on power, default levels are completely wrong at like -20v. Resetting help but not precise - still about ~1v off. Re-calibrating levels get it right but immediately after i switch back from GND to AC or DC level line is completely destroyed showing nonsense. Interestingly, after reset(+-) I can at least still see sine wave from oscillator.

So I started investigating it and according to manual checked everything from scratch. First voltages:
vbus: 5.06v
V+: 4.72v
AV+: 4.7v
V-: -4.02v
AV-: -4v
V1: 0v
V2: 1.12v
V3: 2.23v
V4: -1.11v

^All voltages seems fine. Then I tested display board alone and maybe this is causing it:
I remember this board worked fine before showing a proper voltage line according to manual.
Some other board pictures:
There is one thing I did and hope this was not cause of problem, I wanted it to run on battery so I connected from that white [BATT] connector to 3x AAA 1.5v batteries and closed/soldered JP4 pad(leaving JP5 and JP6 open). Looking at the board connections I don't think this should be an issue and oscilloscope did boot and worked same with batteries as it did with usb adapter. But mentioning it just in case. Problems happens both on batteries or adapter.

To me look like display board alone seem to have an issue but I have no idea why, really hope I can still fix it with your help so thank you in advance.
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