SST03 troubleshooting

[peranders]

I'l loosing track here. Can you measure once again please.

R10 and all transistors.

[Maarten Stevens]

I will post the schematic with all the voltages later... this should help I hope to identify the problem...

[Maarten Stevens]

Hi Peranders.
I have written down all voltages, and identified the fault. Voltage between D2 and D3 was 32V (good), voltage between D3 and Q1 was -0.4V. Hence I guessed there was something wrong with the caps. So I removed C4 and C5 and it worked.

Unfortunately, I am not sure if I am where I want to be.... I get a blown fuse now upon startup with transformer and PSU....  :?

[peranders]

Do you get a delay now? Have you replaced the caps which must be made of polyester?

[Maarten Stevens]

I think it is delayed (I hear c-click I think). The caps I had in were 1uF 63V WIMA....

[peranders]

I get a blown fuse now upon startup with transformer and PSU....  :?

What kind of fuse, rating? Fast, slow?
Transformer size?

[Maarten Stevens]

Hei Per Anders,
I was using a 1.25 slowblow, which blew all the time. I have now replaced for a 2A and it works now. The transformer is 400VA.

I am still running without C4 and C5 positions filled, what is the impact of that? How can I insert a suitable cap here?

Also I see sometimes a little spark around the relays... this doesnt seem to affect it though, as no fuse is blown, and the psu starts up normally. What can this be?

Thanks,
Maarten

[peranders]

The 1 uF caps are there for creating a delay - a soft start.

[Maarten Stevens]

I have replaced with another 1uF 63V WIMA... then K2 doesn't activate again!

So: it only works with C4 and C5 empty, but I do see a spark then inside K2 relay (and of course there is no softstart then...)

[Maarten Stevens]

what is the required rating of the caps in C4 and C5?

[peranders]

63 V, polyester is enough. I must say you have a mysterious error.

[Maarten Stevens]

I haven now also tried a 250V MKT in that position... still doesnt work. As the designer of the circuit... what could be the culprit?

[peranders]

When the cap is inserted how many volts across it do you get? When you test this do you have a 24 volts power supply or do you use the mains voltage?