Pls HELP, fried my analog board...

[Gab04]

I accidentally touched the unit's 9V supply voltage with my probe (GND I guess)

The screen works fine but measurements are broken, the display looks like the pic.
After a few (dead) seconds the trace jumps to the top of the screen and stays there, voltage reading usually goes to 51V.

Here are my test readings on the analog board:

Input 9V
V+ 8.14
V- 0.63
AV+ 5.03
AV- 0.81
V- 0.63
V1 2.22
V2 4.43
V3 2.56
V4 3.43

Board No. PN 109-15001-00F

I ordered a replacement unit just in case but I hope it is repairable.
What ICs do I need to replace? U5 maybe?


Thank you

[jye1]

The negative voltage was gone. Maybe U5. Was it hot?

[Gab04]

It was burn-smelly after the incident, now not hot, when I turn the unit on.

Microscope revealed a burnt point, chip also puffed a little...

[Gab04]

Chip replaced now.

Values:

Input 9V
V+ 8.14
V- -7.76
AV+ 5.03
AV- -4.94
V- 0.63
V1 0
V2 0
V3 0
V4 1.62

Still not OK, but getting closer.
I see measurements going, just the trace was at the bottom. See Vavr and other values on the pic, in the negative region about 5 div level constantly.
Freq value not displaying, although I can get the trace triggered.

What's next? I bought all the chips that are on the analog board, so that I can replace whatever else needed.

Thanks for the reply

[Gab04]

Double checked V4, it is positive instead of negative.

Also, when I probe V4 with the multimeter, the small red LED D1 lits up on the back of the digital board.

[jye1]

The voltages are good. V4 should be around +1.6V so your measurement is correct. Please set couple switch to ground and do VPos alignment and see it the trace goes to normal.

[Gab04]

THANK YOU

Everything is back to normal

Now I'll have 2 units