Console woes... any help/guidance?

Hey Guys,

A close friend of mine has a Soundcraft 6000 console (32 channels, 24 busses) that he has had on permanent loan from along mutual friend. It has worked fine for years, a couple scratchy pots, switches, normal wear a tear etc.

The other day he smelt that dreaded burning smell coming from the PSU and the bipolar 17VDC rails went down and the console stopped working (as to be expected).

Off the top of my head I suggest it may be one of 2 things, either the PSU had gone down from wear & tear, bad caps etc or that something in the console is pulling it down.

On closer inspection it seemed that the PSU had been loaded down as one of the secondary windings on the transformer had melted at the molex header and the trace where it connected to the bridge diodes and the connection was blacked and broken/melted through. I desoldered the caps for good measure and checked they were in spec and they are A ok.

I then repaired the PSU by cleaning up the chared remains and jumped the burnt out trace and on power up the PSU came back to life, all the voltages checked out fine and all in spec to the documentation, though with no load.

It made me think that something inside the console is loading down the rails and as expected when it was reattached to the console it did exactly the same thing, the rails seemed to power up and then sagged and are now dead again.

The dilemma is that it isn't his console and the owner doesn't want to sell it, but it clearly needs work and troubleshooting a console isn't going to be fun and as much as I want to help I doubt I can give him more than day of my time to systematically go through it all without having to charge him... which he can't afford right now...

My next course of action would be to repair the PSU AGAIN and then painstakingly look for visually damage on each the PCB's and then if they look okay to slowly plug each channel in until the PSU gets pulled down again and hopefully find the culprit that way... unless anyone with console restoration experience has any other suggestions.

Thanks in advance

Matt

Repair the PSU. -You'll have to either way.

Measure for a resistive load at the console end -ther between +17 and 0V, or -17 and 0V, or +17 and -17.

Then MEASURE the current when you reconnect it. If in doubt -and for protection- try wiring a couple of 10 ohm 20-watt resistors in series with the ±17V lines, then measure the volt drop across them. Multiply it by the resistance to get the current, and if there's too high a load, you should see it easily, without caning the power supply.

Unplug modules inside the console if it turns out to be there, this really won't be all that tricky. -I can usually get that sort of problem nailed down and fixed in less than an hour... you've got PLENTY of clues to go on, and you'll feel really good about it when you're done. -It's not as bad as you're imagining, I can almost guarantee.

Keith

I have repaired many power supplies over the years (not console ones)

Without the console, test the power supply it can still be bad.

Now what is the is the power supplies rated current?

What does the console draw current wise + and -?

If you do not have access to an active load bank you can make a simple resistive one

What I would do, get the supply working again then load it at about 1 amp on both rails with a simple resistor load bank. Maybe two 20 ohm of the right power rating

resistor value needed would be voltage divided by current

DC power = voltage x current

now connect the power supply to just the load bank

first load it at about 1 amp

load it at say 1/2 console current (add resistors or make a different test unit)

then load it at console current

Look at the rails with a scope set to AC for ripple at different currents if it works at low current and fails at higher that is a hint of what to look for.

Is there an schematic or brand and part number of the supply you can link or even a picture.

Hi Guys,

Thank you both VERY much for your insight/wisdom and thoughts.

Keith I'll have to get the PSU back and repair it as you said. As I mentioned before it seemed to be that their was/is and incredible amount of heat build up on the power transformer secondary where it connects to the bridge diode on the +17V rail CON 5 on the schematic which can be found here: http://www.crystalclearrecording.com/downloads/soundcraft/CPS450/schematic.jpg

It is a Soundcraft branded CPS450 Power Supply.

I will try ohm it out as you suggested on the console side in the next day or 2 when we are both free and I can get over to my mates studio.

Gus, RE specs. The PSU is designed to put out a max of 3.2amps on each of the 17VDC rails, I'll need to try and find out what the console in it's current configuration draws (it has 36 channels, 24 busses).

Thanks again for the input, it is MUCH appreciated.

Matt

without having read all the thread the supply wire comes to my mind (soundcraft and TAC always ring the same bell in my head). Check this for a short

I have not laid my hands on a 6000 so this may not be pertinent. However, I worked on a newer model 32 channel board that was losing it's +/-17V rail. The problem was heat build up on the ribbon cable that connects all the strips together. If this board has a ribbon in it, the solution was to divide the board in to thirds and run a wire directly from the multipin connector to each third. Soundcraft has acknowledged this problem, but like I said, it may have nothing to do with the 6000.

Even though the caps are in sepcs I would suggest to replace them all if this has not been done in the last years. When I bought my Soundcraft-console last year the PSUs were the first things I totally restored.
It had so much dust inside that I was afraid it could catch fire. So intense cleaning was the first action so I could at least take a look at details.
And there were two burnt down traces as well P48 and - I think - +7,5V. And since the caps all looked a bit bloated I replaced them. After all they were over 20 years old! Then I repaired the traces and all worked well again. Just wondering why the fuses didn't blow.
Now to trace the problem on your friend's board it could also be a good idea to try a service-PSU with adjustable voltages and test the +-17V alone. These should not blow up as problems occur. And then you could go for the board with all modules taken out and then put in one after the other, maybe only one module at the time. This could already make things clear. And if the problem mentioned by stinky is not the problem with that board it sounds like a good idea to do anyway.