exxos's Atari, Amiga & retro forum

OK. Looks like the PSU is having "issues" Smooth output but +5v is 4.64V and +12V is 11.4V.

I'd better recap it.

Well, there's your problem...

I've got all the caps in stock, except for the two 220uF 25V ones. So I've replaced everything but those two for the time being.

The modular power supply is easy to take apart so when I have the replacements I can can do those. All the other caps had leaked so those will have done too.

Hmmmm, bulgy!

OK, the +12V and -12V are now in spec. The +5V is still low, at 4.77V though, so it's probably those 220uF 25V caps. Still, it's better than it was.

I'll put the order in now. Of course, I'll not get them until Monday now.

A quick question for those of you who understand power supplies:

Would failing caps reduce the ability for a PSU to supply current or regulate a voltage?

Basically, the Aztec manufacturer power supply in the Apricot FP is failing to keep the voltage at 5V. Would the fact that the two 220uF/25V caps may be dodgy prevent the proper regulation?

If not, what other fault may be causing this?

stephen_usher wrote: 10 Dec 2021 09:59 Would failing caps reduce the ability for a PSU to supply current or regulate a voltage?

Yep. They are part of the feedback loop. Similar as ive shown on my website, failing caps can cause huge voltage ripples where the output is more like AC than DC. Failing caps cause huge voltage spikes which will kill whatever its powering or the PSU overvoltage protection will kick in and power down etc. Some PSUs can even explode.

back to basics :

The diode bridge keep the voltage positive, transform the sinusoid from main into a what I would call a McDonald-oid

And then the capacitors plugged accross the Positive and Ground output do smooth the McDonald-oid into something that ripple between the max Voltage and a lower point (Vmin) that depends of the discharge rate of said capacitor

Thus the answers to your question, to me, is that failing capacitor would fails at regulate the voltage in that it would have taller ripples (between Vmax and a lower Vmin), hence a lower equivalent DC voltage.

edit: ha, too late

Well, the voltage is very smooth and constant (according to the oscilloscope) with no spikes at all, merely not able to keep a consistent voltage.

On or off load ? How much you loading it with ? Is there a schematic ?