Sjöström Audio DIY forum

With new rectifiers, the psu seems ok. I soldered the amp section in, and it does not shut down like before. It makes a mechanical 50hz humming sound, and e29 lights up with the thermal camera.

What should I measure next to make sure it is ok? I sort of assume that this is a temporary thing until the new rectifiers brake down.

Switch over to "diode" on your DVM and measure the diodes in the rectifier bridges. If you read near zero, the you probably have broken diodes => change the parts.

I have measured all the electrolytics in the psu, and all the resistors. When still on the pcb, they all measure the same.

When I watch the amp power up with a termal camera, the only thing really different is the rectifiers. The two in the middle (the two failing ones) gets really hot. When I measure resistance across these, I get almost a short between the ac and the positive on the two failing ones, but the working ones show several megaohms.

Should I simply order new ones, or do you think these are only symptoms for another error?


Thank you for following me through this so far!

One positive regulator works the other doesn't afters one time. It means that most parts are in the right place. The two halves of the pub's are indentical so compare especially how electrolytic caps are mounted. You have probably made same mistake for the negative regulator.

This is at the output of the lines from the psu that i have cut previously.

I will have a look with a thermal camera.

Is this the output from the regulators? Is the voltage at each amplifier zero(should be since you have cut the connection)? Can you notice any heated component?

These are the values. I noted the fuse number on the rails i measured. (In parenthesis the values after some seconds, when the amp fails)

F1 +13,8v (5v)
F2 - 13,8v
F3 +13,8v
F4 -13,8v (-5,5v)

Per Anders, here is what was at play. The DAC board was actually drawing more than 100mA. The choke was designed for this rating, which wasn't enough. Hence the choke saturated and behaved as a resistance. Installing a choke with higher current capacity has solved the issue. Thanks again for your support and for the regulator.

What is the values of the output voltages?

The two in the middle. The leds stop shining after about five seconds.