Question about vcc at IC wine cooler psu

[billbyrd1945]

I'm working on two identical 12.5v power supply boards for a dual Peltier wine cooler. One seems to be working while the other one doesn't. I barely know enough to ask a good question, but here goes: The voltage at vcc on the IC is a little over 5vdc on the working one and a little over 12vdc on the sick one. But I don't know if that condemns the IC, or if the problem exists before the IC. Is there some way to determine this without desoldering it? (I have oscope and multimeters) Thank you.

link to data sheet:
https://www.mouser.com/datasheet/2/115/AZ494A_C-271601.pdf

[hermit]

It looks like that chip can use a voltage up to 40V at VCC so my question would be, "Are you absolutely certain that those boards are identical?"  Look for revision numbers, etc.

[billbyrd1945]

Yes. Both boards are PCB90829F1. Since my last post I've been checking the two power transistors on the non-working board. They are 13005D. In searching for tests, I find seemingly credible sources with two conflicting methods. One school is testing diodes B to C and back, and testing B to E and back. My transistors pass that test. But the other school is to do the same tests with one additional test from C to E and back. That test shows my computers to be bad. Maybe we can settle it here on the forum.

[billbyrd1945]

Here's a drawing that shows how I understand the test to be done. Several videos show it done this way. Conflicting videos show that the last transistor in the drawing should be OL so that the middle and right pins would pass no voltage in either direction. One method condemns my transistors while the other says they're good. What do you guys say? I have no schematic. The markings are all I have.