M-Audio powered speaker turn on problem

[Jazz P Bass]

It looks like it would be a real PITA, but could you possibly trace where the 12Vdc for the relay is coming from.
It sounds to me like a timing capacitor issue.

A lot of these 'pack em smaller' type units have some real boo boos when it comes to component layout.

Like placing electrolytic timing capacitors next to heat sources.

[Bigdrums]

I followed the relay traces to a 100uf 16v electrolytic that checked good.
I tried turning on the unit without the electrolytic in place and SOG it turned on, no variac but light bulb limiter in line
I remove the light bulb limiter and it won't turn on.
Is that maybe because the bulb is slowing the current in-rush?

[Jazz P Bass]

I would ditch the limiter.

What circuit does the 100uf/ 16V cap attach to?
In other words, what turns on the relay?

[Bigdrums]

Very difficult to say what turns on the relay. Its a double sided board, small traces disappearing under various components. I'm wondering what risk there might be by just jumpering the relay since that seems to be where the issue is? I don't know for sure it would work but I think it might. The relay I'm referring to is just before the rectifier.

[g1]

It will work but you will lose the protection if there is a malfunction.

[J M Fahey]

I would bypass the relay with an NTC thermistor and check whether it now turns on.

Use an inrush current limiting thermistor pulled from an old unused PS smps.
This is just for testing, you may laterreplaced the "borrowed" NTC where it belongs.

[Bigdrums]

The thermistor worked perfectly! Thanks
What does NTC stand for?

[The Dude]

Negative temperature coefficient.

[Vinh]

Can someone give me the value for the capacitor C7? The big brown cap on the far right in the picture above next to the 8 pins IC chip? Thanks in advance

[tedmich]

Can someone give me the value for the capacitor C7? The big brown cap on the far right in the picture above next to the 8 pins IC chip? Thanks in advance

this one?



its an old thread I dont have one in front of me, can you take a clear picture?