cps450 or soundcraft 6000?

[matiss]

Hello,
it seems that every once in a while the mixing desk or the psu have problems.. (24 channel, 16buss)
2 years ago I did a recapping of my cps 450 because I had noise and crackles on the sc6000, the caps were chosen a little bigger according to someones competent advice. Noise&Crackles were gone after the recapping. But in a short time after, the 17V rail shutted down when firing up the psu connected to the desk. Disconnected, the psu seems to work fine, which leads to look for the problem in the mixer, am I right?
I find out that when firing up and shutting down the psu disconnected, then waiting for the power-leds on the psu almost to be darkened, then connecting the cable to the desk and firing it up again, everything works fine. So it it is some kind of start-problem, as if there was too much current needed for firing up, whether it's the mixer, or the psu to weak..
I have now taken out all off the 24 channels, master section and the buss-channels, it seems like it needs only any 3 channels, or any of the buss channels, or even just power connection to the VU's to be connected to cause the psu 17V rail to fail.
When there is just few chanels connected it seems there is just one of the 17V rails that Fails, while when you go on connecting more, both rails fail.
I'm aware this looks like looking for a needle in a haysack, but for some technician this might have a simple and obvious reason. If so, I'd be happy to get a hint.
Many thanks!

[matiss]

just one more thing: at the connector pin 1 where there should be +17v I measure 12,7V, and at pin 3 there is- -15,7 instead of -17V.

on the Psu pcb there are two trimmers, I wonder if if I can set the voltage there, but even if you can, what might have been caused the voltage to be reduced?

[matiss]

measuring the power at the psu board in the mixer, the power of the 17V rails drops with every module added till it fails.

[Jim Williams]

That supply is only 3 amps, not enough. Replace it with a larger supply or repeat.

[matiss]

Hmm, but the mixer used to work for a long time with that psu, and as far as I know, it's that psu wich comes with that desk, I think according to soundcraft, it is with the 24 buss 48channel and more that you need a bigger one.

[matiss]

Just for those who experience similar problems: when the described problem occured the first time, a few people in this forum already told me, it sounds like a bad soldering connection. I did resolder the new caps after this, and still had the problem after a while.
In the mean time I exchanged the powerregulators and the rectifier diodes just to see what happens, Voltages were closer to specs as a result, but still the 17V rails shutting down when connected to the mixer (+17 shutting down first).
In the end, I thought maybe I did misunderstood some advices to increase the capacity of the smaller caps, and this causes the rail to shut down... So I was just up to exchange the caps to the original values when I discovered the bad solder connection at the first of the caps... I should have paid more attention to this!
I also experienced that with my standard solder-iron which goes 450°C it was very difficult to desolder the parts in the PSU, I probably don't use the proper tools for the job.
Anyway, it seems like all the trouble was due to a bad solder connection at one of the smaller caps.

[GJC Designs]

Thanks for the information on how you traced and solved the problem.
It is always useful to get information on what the solution to a problem has been and also how the problem was solved.

[s9dd]

I have the same issue with a 24:16:2 S600.

+-17Vdc drops to 14Vdc when loaded with the connsole. New caps etc going into the PSU unit.

Want to know if there is a set up procedure for this PSU? Manual is not helpful on this point.
Do we power up, trim, then load? Or load, power up, then trim? Is there any merit in one then the other?

Secondly, removing the master module, these voltages climb to 16Vdc, so it may that there is (still) an issue I have yet to drive out that module. Is there anything I should be looking for on the master module that would cause a 2Vdc drop to both rails?

Long shot asking, but all clues/ideas welcomed at this point.