Salas SSLV1.3 UltraBiB shunt regulator

[gaszto]

I've replaced both of BC560C. Q2 Vbe 166mV Q3 Vbe 3.45V
M1 voltage between leg 1-3 is 11.56V (same as output voltage) M2 voltage between leg 1-3 0.585mV. Rload checked 99.6Ohm

 

[Salas]

M1 must be wrong type or broken

 

[gaszto]

I don't believe. I've replaced M1, and everything is the same. M1 voltage between pin 1-3 (Gate and Source) is 11.56V, and the output voltage is also the same 11.56V

 

[Salas]

What about the trimmer?

 

[Salas]

Q1 Vbe?

 

[gaszto]

Trimmer is ok, Q1 Vbe is 380mV

 

[Salas]

Leds are alight?

 

[gaszto]

Yes, both of them.

 

[Salas]

How much mV drop between R7 pins?

 

[gaszto]

I measured 0.5mV between the two leg of the R7. I measured one leg to GND is 0mV the other leg to GND is 0.5mV Thanks for the help Salas, it should be something very special issue...

 

[Salas]

Just measure across its own pins. We need 0.27V at least across R7 to have 1mA Voltage ref current. More is ok. If not so, J2 isn't working well and the Vref system (Q2 Q3 etc) is under-biased.

 

[gaszto]

Ok, next I'll replace J2 at the evening. Or could you suggest some measurement before the replacement? I have a basic oscilloscope as well, so I can measure more things. I used solder wire with silver and really hard to desolder components...

 

[Salas]

With power off and still soldered on board you can measure Ohm between drain and source pins on the JFETs. Should be decades or hundreds of Ohm but not shorted or kilo or open. A typical healthy PF5102 can show 70-100 Ω or thereabout.

 

[gaszto]

I measured all of the JFETs. 95-100 Ohm all of them... One thing. The minikit contained Nichicon Muse bipolar capacitors C2, and C3. Is it ok?

 

[Salas]

Yes Nichicon ES (BP) are alright for this reg in those positions. Although the RDS looks good in the JFETs we should also see them producing enough voltage drop on their respective 270 Ohm source resistors. Meaning 1-2 mA bias or about. Solder joints must be good, resistor values must be good, JFET gates must be good.

 

[Salas]

Do you have an M2 to replace? Mosfets can be compromised unconsciously by static.

 

[gaszto]

I didn't change M2. I changed M1. for the test I put another 100R load parallel, so now the load is 50Ohm, should be 100mA load. The voltage dropped from 11.56 to 6.5V

 

[Salas]

That's good showing that at least the current limiting function works.

 

[gaszto]

Yes, I have a current limiter But according to the formula the current is limited 125mA and the load is 100mA. Can I measure something on the M2 before the replacement?

 

[Salas]

You measured Vgs and it wasn't good before, I think?