SSLV1.1 builds & fairy tales

[Salas]

1. Yes for filtering effect. Noise knee 1/F point is defined by the semis physics.
2. I had kills of 25V JXXX JFETs at the base of Vref in high Vo & high cap experiments.

 

[schubert]

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.

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?

 

[Salas]

That had to be done, OK. 3.6V spells VGS potential only. See if you got any voltage drop across the outermost trimmer pins.

 

[schubert]

That had to be done, OK. 3.6V spells VGS potential only. See if you got any voltage drop across the outermost trimmer pins.

Only 0.189V, which at the current trimmer position gives about the same 0.1mA through the trimmer as I had through R103 before.

 

[Salas]

What happens if you will short the trimmer with a wire for a test?

 

[schubert]

What happens if you will short the trimmer with a wire for a test?

Still 3.6V.

 

[Salas]

Is Q304 a BC550? Is it flanked by a couple of 2SK117s?

 

[Salas]

If yes, does Q304 measure ~0.6V Vbe? Is R304 1 Ohm and not 1 kOhm by mistake?

 

[schubert]

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.

 

[schubert]

Vbe for Q304 is only 0.026V, which appears to be the difference between Vce and Vbc (both around 4V) - is that correct?

 

[Salas]

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.

 

[Salas]

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.

 

[Salas]

Retouch it or exchange it (Q304 BC550). Do Q305 also if no cigar.

 

[schubert]

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).

 

[Salas]

Q306 Vgs=0 is no good at all. Lets see then.

 

[schubert]

Replaced Q304 & Q305, no substantive change - I'm at 4.0V now.

 

[Salas]

Q306 output Mosfet, check it. Basic Amplifier Repair - Transistor Test Applet Link (For PMOS as here reverse the leads).

 

[schubert]

Q306 tests OK - open circuit reading for all combinations, and 0.67V diode reading between leads 2(+) and 3(-). Q301 also tests OK.

 

[Salas]

If all semis are OK and all passives are OK and all soldering is OK it should be working, its no proto. Something is abnormal. Inspect all elements for value and Vbe Vgs again, do continuity tests for tracks and pins. More I can't think of.

 

[schubert]

OK thanks for your help Salas. If I find the problem I'll post.