Soundcraft Folio 16/2

[bfisk]

Hi all,

I've got a real headache of a fault with this mixer. After removing about 6 duff chips all the others seem to be working OK.
There's a ripple on the +ve supply which I suspect is coming from the board somewhere. The power is clean where I've cut the tracks to the rest of the board.
Measuring the resistance to ground, the +ve is approx 2K whereas the -ve is >1M.
Other than removing every chip on the board I'm at a loss what to do next. All the existing chips output pins are at 0v so they look OK (not including the cmos switch and the level meter chips).
I don't have a schematic either so trying to trace the power to maybe isolate sections of the board is nigh on impossible!

One other thing, the 5532 op amps run quite warm to the touch and I don't know if this is correct?

Help!

Bob

[Leolabs]

Seems that something wrong with the -ve voltage rail.What is the output volatge of both rail???

[bfisk]

Hi,

The +ve is approx 16.8v (it does vary intermittently from approx 16.6) and the -ve 17.0v on load, and both 17.0 when off load.

Bob

[moamps]

Hi Bob,

From my experience with Soundcraft folio consoles, power supply on ICs should be +-15V. Generally speaking, malfunctions in these consoles are most often caused by the power connector, regulators ICs (7815,7915), bridges and headphones opamp.
Anyways, I have the schematic of the 10/2 console, which is similar to yours. I can send it to you if you drop me an email.

Regards,
Milanl

[Eva]

It's normal for 5532 op-amps to run quite warm to the touch, particularly when powered with rails above +-15V.

Check for bad electrolytics in the +Ve rail, this may be causing excessive current consumption and voltage drop in the power supply. Ovbiously, the faulty capacitor, if there is any, is going to get quite hot.

[bfisk]

Thanks for the replies guys,

The supply lines are actually meant to be 17v on this board. The regulators have an led between them and ground to up the voltage.
I do have the copy of the 10/2 already thanks and although similar it does have slight differences, the PSU being one.
The headphone and o/p op amps have been removed as they were faulty.

OK on the 5532 running warm, I thought that should be OK as the ones left in cct appear to work fine audio wise.
I've done tests with hot air and freezer on all likely components with no success but the +ve voltage varies intermittently on it's own, the ripple also varies and at sometimes almost disappears!

I don't think it's a psu problem though. Both regs have been subsituted along with smoothng caps. The waveforms on the dirty side of the regs are identical, as well as the voltages, so the bridge would appear to be fine too.

It would be good to know whether the resistance readings I'm seeing across the supply lines are correct. Why the +ve reads 2K and the -ve >1M is a bit odd (tracks cut to the psu section). There are other feeds that just use the +ve eg the pfl led's but nothing I can see that would give such different readings?

[Eva]

I was talking about the dozens of electrolytic supply decoupling capacitors that are probably spreaded over all the modules or the board (I don't know the exact topology of that console). The situation you describe matches quite well with what happens when there is a bad leaky capacitor somewhere.

People from a local service shop told me that in extreme cases, with 32 channel consoles with a shorted rail, they just connect a 5V 20A PC power supply to the faulty rail in order to make the faulty capacitor explode, and locate it by the way, thus saving the work of checking each channel. I wouldn't do that, though.

Have you checked how much current is being drawn from each rail of the power supply? If the power supply is working properly, then this voltage must be either due to excessive current consumption and regulator protection triggering, or due to a false contact somewhere in case current consumption is normal.

[destroyer X]

And very practical, mui bien, sin embargo una gran idea.

Also can remove the Chips, if the are not soldered in the board, and invert polarity for a couple of seconds.

This will guarantee explosions..... wonderfull that...the repair man revenge!... killing them all..hehe

regards,

Carlos

[bfisk]

Update to the problem.

After more hours of head scratching (this has become a labour of love now) I've dicovered that shorting out the LED on the 7815, which grounds the regulator, stops the ripple and all hums disappear. This is good news, but why?
The voltage on the +ve line drops obviously to 15v and the board seems quite happy to work with 15+ and 17-.

Now, as I've said, the regulator has been swapped, the LED's have been swapped and the 6K8 resistors that feed them checked OK. The +ve line has been loaded up externally from the board and shows no ripple at all (with identical current draw).

In all my years of mending stuff ths one takes the buscuit!

Bob

[SoundQuakeAudio]

I had a problem too with my spirit folio,just inherit the unit without PSU..i have a xformer with a 19-0-19 vac 1amp. and top it temporary into main lead..humming is produce when u lift of mic.fader 1-6...with or without input..i had replaced possible broken OP amps and capacitor in main supply ckt.and nothing happen..i dont have schematic nor service manual..anyone experience this before or even now? pls..help kind-hearted people..
Thanks..