Soo... this thing is a Korad power supply, right?
Schematic:
https://elektrotanya.com/korad_ka3005p_velleman_labps3005d_power_supply.zip/download.htmlConfirm if this it the one for you device.
In PIC2 it looks like a bridge rectifier was very much overheated. And there seems to be corrosion/dirt/residue a bit everywhere. Confirm the bridge is still on the other side of the board and measures fine.
Are all voltages as expected?
- Transformer outputs 36VAC, 15VAC, 10VAC;
- DC regulated lines are +12VDC; -12VDC; +5VDC (in 2 different places because two 5V regulators) +3.3VDC. Double check the voltage over the 3 'big' 2200µF caps -> how much is it?
Have you measured the 7.8V on the output with a multimeter or is that what the displays tell you? Don't trust it, measure yourself and report please.
Most likely possibilities:
- Somehow the 36VAC from the transformer doesn't make it to the output anymore.
- The output transistors are dead (Q1 & Q2, driver is Q3 on the power board and this in turn is driven by Q4 on main board)
- Something is wrong with the analog/digital converter that measures the output and the CPU does not receive the correct information. (D6; U5A; U6A)
- Something is wrong with the D/A and the CPU can't set the output. In this case I would expect to still be able to set the value on the display (U5B; U6B; U7A; U7B and then Q4 and Q3)
Can you read the CPU model on the chip?