Debugging XAPS 500W power supply issue

My Antek AN-6224 600VA transformer is providing 24 VAC as expected, but I am only seeing 2 VDC output. Any advice on how to debug? I'm assuming everything up to the power supply board is working as intended (I do have a "soft start" board before the transformer which DOES seem to be engaging properly given I am getting an expected measurement from the transformer -- I am not so sure it's a good idea to omit the soft start because the transformer is 600VA so the in-rush current COULD throw my circuit breaker to my house).

I might have heard popping sounds the first time I turned it on, but it looks like the polarity on the capacitors is correct.

Is there a way for me to check whether the problem is the diode bridge OR the transformer to help narrow things down?

(Maybe I can measure the output of the diode bridge WRT ground and see whether I end up with some DC-like signal -- I don't have a scope though...). I don't see any obvious shorts or soldering problems on the board itself, and the capacitors don't look burned or swollen.

I also have a spare set of equivalent caps I can throw on there if it comes down to it...
I have a 10A fuse on the AC inlet, which didn't blow. I removed the soft start as well.

Wondering also how safe the capacitors are? I've been acting really paranoid around them because they are pretty big capacitors. They are 4x 6800uF 63V electrolytics. How long do they take to discharge when disconnected? How bad of a shock could I get?


Paid Member
2003-06-12 7:04 pm
Maine USA
...I am only seeing 2 VDC output. ... How bad of a shock could I get?

If we believe you: a 2V shock. You won't feel this on skin, maybe not on tongue.

How long? Put your meter on it and watch!

However should be 35V. So you may not be measuring right. Are you sure the meter is on DC Volts (not AC, not amps)?? You have solid connection with meter probes? Battery in meter is good?
I don't generally give 24V or 35V much thought, safety-wise, but your results may vary.

If you know what polarity your meter uses when testing resistance, or it has a diode test function, there are a few other things you could measure before replacing parts.

But right now the likely causes are down to 1) blown parts, 2) faulty meter, or 3) pilot error.

Cheers, Rick
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Paid Member
2003-06-12 7:04 pm
Maine USA
> no shocks.

Depends on your sweat. On a hot and humid day, 12V car battery gives me a startle. OTOH I had a very dry-skin friend who did not feel a 117V screw-up which bothered everybody else in the room. I (recklessly) told him to lick his fingers and try it again. He agreed "YOW! Now I feel it!" (I was fairly sure he would only be shocked through hand, not heart, but it was a stupid thing to do.)

In most situations, 24V is allowed to be exposed to consumers. In the US we have a nominal 24V speaker distribution system because someone thought the 70V system should not be accessible except to trained technicians. However the 110V pulse for telephone ringing was often exposed on old/broken telephone connectors; standard from long-long ago.

Depends on your sweat.

Reminds me of first foray into valves.

I was well ahead of everyone in my electronics class so asked if I could build a valve guitar pre amp and was told ok.
So built it up and it didn't work.
Unplugged it and touched the circuit and got a good belt.
My tutor said the capacitors stayed charged and that's why I got the shock.
He said to discharge the capacitor with a resistor.
So next time I duly discharged the capacitor.
Touched the circuit and got a big belt.
I had forgotten to turn it off !

That was 40 years ago and amazingly I am still in electronics and still alive !
I always add an a resistor and LED on my B+ lines to give a visual indication of high voltage.