Help with faulty Valley 440

Hi,
I have a faulty Valley 440 comp/lim on my bench that needs repair, but I really can't understand where is the problem.

Manual and schems are here: http://www.galaxyaudio.com/products/PDF2/440.pdf

Basically it has a strange behaviour, sometimes there's no output signal, other times there's out signal but no compression, led bars go at full scale after some juggling with pots, etc.

I started looking at psu and it looks good, I have approx +15V and -15V from 7815/7915 to ground, but when I try to measure voltage from +15 to -15 my meter goes mad and after a while the fuse burns...
Also if I measure +V and -V on opamps I get approx +15V instead of the expect 30...
Any ideas?
Thanks
Frank

never worked on one but it "sounds" like it might be a bad solder connection, connector dirty or broken wire etc. I post this because you posted

"Basically it has a strange behaviour, sometimes there's no output signal, other times there's out signal but no compression, led bars go at full scale after some juggling with pots, etc. "

Thanks Gus,
I came to the same conclusion but I checked almost everything, however I'll give another look. I simply can't undertstand why I can't measure between -15 and +15 terminals...
Frank

Hi!

Maybe a bit far feched but have you checked the diodes after the voltageregulators?
Another tip is so disconnect the PSU and putting two 10k resistors to GND and then check if you are unshure.
If the ICs are in sockets see in anyone has "popped" up alitle bit.
(Try pushing them all down).

What is the bluredout thing in the left corner of the PSU page?
Is the jumper J1 pressent?

Good luck!
/Hampus

Hi Hampus!
Thanks for the answer!
Those diodes after the reg. look strange to me, I have 0V across them... Maybe I should try by removing them.

J1 is present, but I didn't understand what bluredout you are refering..
Thanks again,
Frank

Hi Frank,
seems that something pulls a short. Separate your power supply (on page 37) from the rest of the circuit (behind diode and cap at 7815/7915 output). Put a 1k resistor between +15v and gnd and another 1k between -15v and gnd. (those 78xx/79xx sometimes behave funny when not loaded). Your meter should read +15/-15 between reg-out and gnd and 30v between reg-outs. Case not, check voltage before 78xx/79xx and gnd. Your meter will give you something like 24v dc (for a 18/0/18v ac transformer, more likely 20v for a 15/0/15v transformer). If not, check/replace rectifier-diodes, smoothing caps across them and loading caps. Otherwise your regs could not stand the 9v voltage drop and suicided before melting.
J1 is only a ground lift, so don't care at this point.

Hi,
I disconnected the outputs of the regulators from the rest of the circuit. I can measure correctly +15V and -15V from each regulator to ground but I get 14V from the output of one regulator to the output of the other (same as with the circuit connected).

Also sometimes when I put the meter probe on on diode or at the input of one regulator I get a blue sparkle...

Should I disconnect the diodes?
Thanks
Frank