Trace Elliot 715 2006 BX007 board

[JonnyP]

Can do. Must have been in a hurry when I set it up.

[JonnyP]

There ye go - fill yer boots.

[J M Fahey]

There ye go - fill yer boots.

Good

Now youŽll be spared the usual:

* junk it and get another one for peanuts at a garage sale

* Mouser orders are post free if you buy more than $12

* have it delivered by truck straight from factory <---- now that would be a good one

* you can deduce its cost in your IRS tax filing because ......

* did you check local Craigslist?

* GC/Walmart is carrying it at the special Winter sale price of .....

* donŽt call until next week, because now we are in the frenzy of Election/July_4th/Thanksgiving/you-name-it

and so on

PS. plus: phone Peavey ... but you already noticed that one

[nickb]

Ah, ok, it's not really a SMPSU - it's a complicatedly FET switched VRS.

The main filter caps, AC rectified C5 (3300uF 100V) and DC C6 (1000 uF 63V) sides have been pulled and checked on an LCR meter, and are a bit low, but within spec.

None of the cans have burst, bulge, or rattle.

The noise is a variable sawtooth, starts of at 108 Hz, but moves around, and is only on the power amp section, post VRS.

Most of the work seems to be being done by a 2sK3216 n-channel mosfet

All the other regulator circuitry is linear.

This really is too complicated - Peavey and their part numbering system, and lack of part numbers on the board make it too hard to service old gear.

I'm not sure I can help you too much but this is my take on it:

It IS a SMPS, just not an off-line one. It's called a buck converter.
IC6A is the error amplifier,
IC6B is the pulse width modulator
IC6D is the sq wave oscillator
IC6C is an integrator to get a triangle waveform for the PWM
IC8 is a half bridge driver
Q17-18 plus T1 for an auxiliary PSU for the high side.

Wow! Talk about doing it the hard way.

So, crucial questions:

1) Are you saying you see a LF sawtooth on the VRSREG?
2) Was is OK ar new and then this has started?

If yes, I might be way off, but it sounds like loop stability might be an issue. If we assume that is was once OK then I would first check the error amplifier for a failed compensation cap - there are enough of them. The error amp is also sensitive to power supply noise judging by all the filter comps.

[JonnyP]

Resale price for this is appalling. The customer has written it off, and I'm doing the same. Well and truly BER. I'll advise customers against repair on these in the future.

Thanks for the help guys, it was fun.