SST03 troubleshooting

[Maarten Stevens]

Peranders... I seem to have a problem with my SST03.

K1 activates, K2 doesn't. Voltage across D4 = 0V (so that's where the problem is).
Q3 base voltage = 40mv (relative to gnd)
Q3 emitter = 25V
Q3 source = gnd

Can you confirm the correct Q3 base voltage?
thanks!

[peranders]

Voltage over R10?

[Maarten Stevens]

Voltage across R10 is 31.1VDC

[peranders]

Good.

Q1, base down to ground? Voltage.

Q1, emitter down to ground? Voltage.

Q2, base down to ground? Voltage.

Q2, emitter down to ground? Voltage.

[Maarten Stevens]

Q1 base to gnd = 24.2V
Q1 emitter to gnd = 24.4V
Q2 base to gnd = 25 mV
Q2 emitter to gnd = 24.9 V

[peranders]

Q2 is broken I should think. Which type of transistor do you use? BC???

[Maarten Stevens]

bc547c...

I have actually replaced Q2 already before, but this didnt fix it.... I will try another one.

[peranders]

You could test the transistor with a diode test. Plus on bas and then check the base-colletor and base-emitter.

D4 is turned right?

[Maarten Stevens]

Just put in another bc547 as Q2... no success.

Q4 is correct position...

[Maarten Stevens]

I also switched the 2 ralays to the K1 and K2 positions... seems that both relays are still functioning.

[Maarten Stevens]

I don't really understand... K2 has 25V on pin 1 and pin 8... shouldn't it activate then?

[peranders]

Is Q3 base at 0 V and also the collector?

[Maarten Stevens]

Q3 base is 60 mV, Q3 emitter is 0V

[peranders]

And the Q3 collector 24 volts or so?

Are your really sure that you have BC5_47, not 57?

[Maarten Stevens]

Yes and yes...

I have tested the board with and without transformer to it (transformer without load)