Laney Ah210 PA mixer power supply

[J M Fahey]

Check added graphic above

[ziggy007]

Isolated 15v easily but 30v to audio chip near impossible on this board layout. (For me anyway)
The 15v rails oscillate between 5.1 and 5.3, the 30v are 6 to 7V.
The phantom pwr is at 45v which taps off the 15v rail prior to diode.
The Vcc oscillates between 10-13v which is not enough. It’s 20v unloaded. Replaced the quasi regulator chip again to see. Same. All components in that cct checked ok.
At a loss unfortunately.
Maybe just buy a new power board from Laney if viable.
Thanks for your help.

[J M Fahey]

Mmmm, what a pity.
Let´s try just one more time, can we?

IF we have disconnected all loads, then any trouble may be attributed (and eventually solved) EITHER to one of the rectifier diodes being shorted or filter capacitor shorted, since for the power supply "all are in parallel" meaning all suck power from the same core OR to Live side of supply, including the funky controller+switcher IC

Now if one important and highly suspect load, the power amp, is not disconnected, then we can´t be certain of anything.

My mistake, I always referred to the generic datasheet schematic posted, which may or may not help you.

Now I downloaded and opened the ACTUAL schematic, sameinstructions asbefore but now more focused.

I *think* you are lucky.
I guess the tracks feeding the (suspect) power amp are already interrupted because I see inductors at each of them which must be external components solered topads, doubt they can put a ferrite bead around aprinted track, so by (carefully) removing them, we can disconnect power amp from supply.
Please check that, and if possible, remove them.

Since they certainly use terrible lead free solder, first apply a little regular (leaded) solder to make it more liquid at lower temperature and then suck solder and remove inductors; then you can measure unloaded supply.

Check these points:

Isolated 15v easily but 30v to audio chip near impossible on this board layout. (For me anyway)

Try my suggestion.
If possible post some inductor area pictures, one above, one below, may clear things a bit.

The 15v rails oscillate between 5.1 and 5.3, the 30v are 6 to 7V.

Either supply is heavily loaded and self turning OFF or primary side is not yet fully repaired ... but we can test that now.

The phantom pwr is at 45v which taps off the 15v rail prior to diode.
The Vcc oscillates between 10-13v which is not enough. It’s 20v unloaded. Replaced the quasi regulator chip again to see. Same. All components in that cct checked ok.

That´s why I seem to be obsessed with "functional testing" rather than a "part by part" search ... unless we find a smoking gun that is.
Do this last test and post results.
I´m kinda stubborn

[ziggy007]

Thanks Juan.
Yeah, it’s killing me too as I hate being beaten.
I’ve just found out I can get a whole new Laney SMPS board for $45 Aussie. That’s ridiculous. Should’ve done that research first. Haha.
I’m definitely going to keep trying when I get the chance as I love the learning of new areas. I’ll pull those inductors. Plainly obvious now you’ve pointed it out.
The fact that the Vcc oscillates to me points that it’s still primary.

[J M Fahey]

Oh, for $45 just replace it; and leave the old board aside for further use.

When/if you repair it, it can make a nice plate amp driving *two* monitors or a powerful PC or TV speaker or ....

A 100+100W amp able to drive 4 or 8 ohm loads is always useful in lots of places.

[Scorps]

Hello everybody!

I have a problem with the same mixer, AH210. Everything works, but the transformer makes a very irritating, high-pitched squeal when turned on. The worst part is the fact that this noise also comes through the speakers!

It can be heard here (I'm switching it on and off):
https://youtu.be/mJrq_HasGLI

I've determined that the sound comes from the transformer itself. When pushing hard on one edge of the transformer, the sound almost vanishes most of the times until I release the pressure.

What can be done to eliminate this noise? At least from the speakers! Although it could still be disturbing in quiet environments.

I also asked for advice from a local electronics specialists' group in Facebook. Some guys told me to dip the transformer in wax or use hot glue. I've never done that, but I have some doubts, since I have to apply quite much pressure on the edge of the transformer to suppress the noise. And should I remove the yellow tapes before dipping or gluing?

Thanks a lot in advance!