Another short update.
I replaced electrolytic capacitors on main board. It was just is time: in few places electrolyte started to eat into the board under the cap, but no traces had been killed yet. One of old capacitors was shorted out (channel 4) it killed this VP0808M transistor.
I will have to find and buy a substitute. For now the cell 4 is out of power.
Meanwhile with new capacitors unit did power up without problems. On power up all lights for cell 4 were off and for cells 1-3 I got:
1) “battery” led solid red (no battery connected)
2) “temp” led solid red and it would change to solid green if I let unit warmup and pressed reset button at the back
3) “average” led is solid green regardless of me putting cell in average mode or not. This is strange.
Voltage outputs on individual cells were all under 0.5v, and readings from average, buffered, 1V and 1.018V did not make any sense at all. Sometimes hung else must be wrong beside blown transistor.
With help of ManateeMafia and Pipelie (thank you, guys), found that DB15 connector that leads into the cell is providing 5V power correctly, but PWM signals on pins 11-14 are missing. I get 5V on pin 14 and 0V on others. There is a high frequency noise there but it is very small (millivolts).
This led me to the module below. Unfortunately I have a hard time opening it, as power pins (red and black wires) seem to be soldered directly into the PCB on inside. Would anyone know if there is a way to open this without desoldering pins? Thanks.