OK I changed them - mosfets are soldered right to the board, but no change - now I get 3.6V instead of 3.7V. Any other ideas?First you got to get rid of the cables to the Mosfets. Only local PCB fit. You got wrong shape sinks for easy side or bottom fit I see.
Only 0.189V, which at the current trimmer position gives about the same 0.1mA through the trimmer as I had through R103 before.That had to be done, OK. 3.6V spells VGS potential only. See if you got any voltage drop across the outermost trimmer pins.
Still 3.6V.What happens if you will short the trimmer with a wire for a test?
Yes on both counts for the parts. The "1 ohm" resistors from Teabag's kit measured 1.2 ohms, but I figured they were close enough. I'll check Q304.
Use the REL DMM button when probes are contacting before measuring so low Ohm resistors. Precision is largely irrelevant in that position, just not to be mistaken for a 100 Ohm or 1K due to color bands.
Vbe for Q304 is only 0.026V, which appears to be the difference between Vce and Vbc (both around 4V) - is that correct?
No, it should be conducting at Vbe ~0.6V and the Mosfets should be conducting at several (~4) Volt Vgs measurement.
Q301 Vgs = 4.55V; Q306 Vgs = 0 (this is the second IRF9530 in this position, so I don't think it's the part). Reflowing all the solder joints made no difference, so I'll try replacing the BC550 with the one from the other kit (I have more at home but I'm at my parents house now).No, it should be conducting at Vbe ~0.6V and the Mosfets should be conducting at several (~4) Volt Vgs measurement.
Q306 output Mosfet, check it. Basic Amplifier Repair - Transistor Test Applet Link (For PMOS as here reverse the leads).
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