Soundcraft 600 fixer upper

[FarisElek]

I've acquired a Soundcraft 600 in decent condition for very, very cheap. So far nothing seems to be terribly wrong besides:

1) LED meter bridge lights up upon start up but doesn't work otherwise.

2) 48v Phantom power light is off on PSU and doesn't work.

3) It's very dirty.


I've cleaned a handful of channels and the Master and they're behaving great, so I'm very excited to get this underway.

So today I've begun checking out the PSU and I've noticed some very odd things and I'm having trouble finding a schematic to see what's up with this thing.

TR2 isn't there and also RECT4 was cut out. I'm assuming RECT4 is the phantom rectifier, but I don't know for sure because I can't find a schematic for the PSU.


Can anyone help me find a schematic or shed some light on the parts that should be there?

Also, any information on ways to improve the PSU if there is anything that can be easily adjusted, that would be very rad. I've read that the PSU can be tempermental and there are things that can be done to improve it, but nowhere I was reading said exactly what that was.

Ryan

 

[abbey road d enfer]

PSU should be either a CPS450 or CPS650, depending on size. I believe yousr is a 650, unless it's an older type, like used on the earlier 800 series.
The CPS450/650 are in the technical documents section.
A quite frequent problem with Souncraft PSU's is the connectors, particularly the DC ones, that get corroded.

 

[FarisElek]

On the bottom it says that it's the Model S500 PSU

 

[Crosscut]

Your first job should be replacing those bulging capacitors, other than that just get it working properly within spec and think about mods later once you're up and running.

You can get going and test the desk without phantom to start with and address that once you've got the audio stable. It is worth considering that the phantom may have been disabled to overcome another problem in the desk itself, so when you do get the power supply fixed and putting out 48v it may reveal some other issues.

Have fun

 

[abbey road d enfer]

You should find the schematic here
https://www.vintageshifi.com/repertoire-pdf/Soundcraft.phpeither 500 user service manual or 600 user service manual (it's the same document).

 

[scott2000]

Your first job should be replacing those bulging capacitors,

Sometimes there are caps that have an outer sleeve that just loosens up and bulges, maybe from heat, and can be just cosmetic in some instances.

 

[Crosscut]

Sometimes there are caps that have an outer sleeve that just loosens up and bulges, maybe from heat, and can be just cosmetic in some instances.

Yes, that's true, it could also be an indication of the length of time the caps have been in there and that it's maybe a good idea to change them to avoid failure in the relatively near future.
I've never regretted changing a capacitor, I can imagine regretting not changing one.

 

[FarisElek]

I plan on recapping the whole thing, but parts are missing and i can't find any info on.The desk is working fine. All the channels I've cleaned are essentially perfect and not even very noisey.

Maybe I'm missing something, but the psu is not on service manual. I've looked through the contents of the schematics and the psu isn't listed on it and I even skimmed the schematics themselves and didn't see the psu.


Scratch that!! I found it on the schematic!

 

[FarisElek]

Also, just wanted to say, I'm not positive, but I think the phantom power rectifier was pulled out because this was used in a TV station (fact) and they maybe wanted to avoid phantom accidentally being sent to dynamic mics, or something along those lines.


Ryan

 

[Nbtone]

I plan on recapping the whole thing, but parts are missing and i can't find any info on.The desk is working fine. All the channels I've cleaned are essentially perfect and not even very noisey.

Maybe I'm missing something, but the psu is not on service manual. I've looked through the contents of the schematics and the psu isn't listed on it and I even skimmed the schematics themselves and didn't see the psu.


Scratch that!! I found it on the schematic!

I recently rebuilt a Soundcraft GB8. I checked all the caps with an esr meter. There were about 300 that tested bad, and when I replaced them my $50 sound board started working.

 

[abbey road d enfer]

I recently rebuilt a Soundcraft GB8. I checked all the caps with an esr meter. There were about 300 that tested bad, and when I replaced them my $50 sound board started working.

What do you mean "tested bad"?
What values were you reading?
ESR is almost immaterial in itself in audio circuits. Did the capacitance value differ much from nominal?

 

[Nbtone]

What do you mean "tested bad"?
What values were you reading?
ESR is almost immaterial in itself in audio circuits. Did the capacitance value differ much from nominal?

The instructions that came with the esr meter give the acceptable ratings. Test them in circuit. Some of the new ones I bought didn’t pass either. I sent them back when they didn’t. The capacitor plague and everything, you know.

 

[abbey road d enfer]

The instructions that came with the esr meter give the acceptable ratings.

How do they know what is acceptable or not? ESR must be appreciated in the context of nominal value, technology, recommanded usage... Good or bad isn't how it works. Audio circuits are very tolerant regarding ESR, but not too much on nominal value and much less on losses and leakage.

Test them in circuit.

So I guess many were considered too lossy.

Some of the new ones I bought didn’t pass either. I sent them back when they didn’t.

Couldn't it be possible that your ESR tester is acting funny?

The capacitor plague and everything, you know.

I don't know what's the "capacitor plague". I used hundred thousands of capacitors, and never met one with "plague".
I've seen ones that had lost nominal value, some that leaked, some that had blown-up, some that were shorted, but I could always identify a failure mode.
In audio circuits, ESR is benign, within limits of course. ESR is important in PSU's particularly smps, but for decoupling or signal transmission, one ohm ESR is perfectly fine, unless if it's a sign of a possible degradation.

 

[Nbtone]

How do they know what is acceptable or not? ESR must be appreciated in the context of nominal value, technology, recommanded usage... Good or bad isn't how it works. Audio circuits are very tolerant regarding ESR, but not too much on nominal value and much less on losses and leakage.

So I guess many were considered too lossy.

Couldn't it be possible that your ESR tester is acting funny?

I don't know what's the "capacitor plague". I used hundred thousands of capacitors, and never met one with "plague".
I've seen ones that had lost nominal value, some that leaked, some that had blown-up, some that were shorted, but I could always identify a failure mode.
In audio circuits, ESR is benign, within limits of course. ESR is important in PSU's particularly smps, but for decoupling or signal transmission, one ohm ESR is perfectly fine, unless if it's a sign of a possible degradation.

Capacitor plague:
https://en.m.wikipedia.org/wiki/Capacitor_plagueI’m just going by what I saw on YouTube about checking capacitors in circuit. I’m not really set up to work on switching power supplies. I just went in and replaced bad caps, and it came to life. Going from channel strip to channel strip caps in the same position on the circuit board were sometime good and sometimes bad, whatever their purpose. Esr meters work.

 

[abbey road d enfer]

Capacitor plague:
https://en.m.wikipedia.org/wiki/Capacitor_plague

Ah yes, I had forgotten they called that...

I’m just going by what I saw on YouTube about checking capacitors in circuit. I’m not really set up to work on switching power supplies. I just went in and replaced bad caps, and it came to life.

What do you mean "came to life"? was it non-functional?

 

[Nbtone]

Ah yes, I had forgotten they called that...

What do you mean "came to life"? was it non-functional?

 

[Nbtone]

Yes. Nothing worked.

 

[abbey road d enfer]

That means the capacitance was largely off, which a normal capacitance or signal continuity test would have shown. IMO, the ESR test has resulted in unduly rejecting perfectly good brand new capacitors.

 

[Nbtone]

 

[abbey road d enfer]

Well, this guy checks capacitors used as reservoir caps and by-pass, where low ESR is necessary, but for signal transmission is almost irrelevant.
A capacitor used for signal transmission in a typical 1k-10kohm circuit could have an ESR of several ohms without any consequence. However, it may indicate some kind of failure, taht a proper measurement of nominal value and leakage would definitely clear.