SoundCraft 600 problem with master module

Hello there!

just a heads up... Im new to this forum and I know this might not be the right place for my issue but mybe some of you might have experience with this and put me on right track before I do some stupid stuff to the board I love as is (stock version 24ch 8gr - 1984)

as well I would like to know how to add photos to the forum so I can show my module...

I am experiencing problems with my soundcraft 600 master module. It has been damaged I guess and someone has done some work on it as the wiring is custom moded and I can not understand what was done. I have problems with the Control Room outputs. Right channel is 1-3db lower than the Left. Mix out, studio speakers outputs are ok - 0.1db of difference in peaks but I belive this is ok.

The module has been factory checked on 20.12.1984 but no information about the servicing later on.. the chips that were supposed to be NE3552 are nowehere to be found on the module and all of them are tl072cp - most the same company and make and some different like malasya and portugal... bla bla.. anyway

I would like to completly change all the components but I only have an Issue 5 redrawn schematics and it seams not to be the same with the naming of the components as they are on my circuit board.

I've been loosing my mind and I dont want to damage it even more before I have some serious information on what and where I should check first to find the problem.

If aynone knows where i could get a new or used working module here in europe I would love to know...

I will appriciate your help very much!!

Thank you!

Dario

dario84 said:

l I would like to know how to add photos to the forum so I can show my module...

Click to expand...

When you write a message, at the bottom there is a line "Attachments and other options"

[/quote] Right channel is 1-3db lower than the Left.
[/quote] To my knowledge, the 600 Master has not changed much over the years; the block diagram has not changed. You should be able to trace the Left and Right signals and find out where they become different.

Soundcraft desks of that age are known for contact problems in the inserts (e.g. in your master) and ribbon wire assembly. You can bypass the insert jack switching contacts by inserting a plug with tip connected to ring.

Thanks a lot for your replys! it means a lot to know Im not stranded with this..

I know about the ageing problem with the desk and I have been cleaning all the connections on it... it helps improoving the sound and lowers the noise level.

but I think this might be a different story.. caouse all the other outputs seem to be right...

now I've noticed there are 6 trimmers on the pcb... who obviously are in the in the amp circuit.. but I  cant tell from the schematic caouse they are named different.. I see they are 1k and in the schematic they belong to each output amp.

I am not really a electrician so I can t tell what they do... I will send  photos of this to make it clear what Im talking bout.

thanks a lot so far!
D

Those trimmers adjust the output symmetry of the signal, not level.
It´s possible that - thanks to the custom wiring and depending on the modification done - an original master module would not work in your desk. You need to find a good tech with expierience in consoles to figure out what´s going on. Without proper understanding any effort is hit and miss which could ruin at least your master if not more.
If you add your location to your profile then we can try to find someone close to you who can help.

jensenmann said:

Soundcraft desks of that age are known for contact problems in the inserts (e.g. in your master) and ribbon wire assembly. You can bypass the insert jack switching contacts by inserting a plug with tip connected to ring.

Click to expand...

That is true, but does not apply there, since the C/R outputs have no inserts jacks nor ribbon connectors in the signal path; everything is on the PCB.

guys so here's some photos to make it clearer what has been done to the module.

this photo shows most of what I found out was different. except the different IC in the place of NE45532 wich were TL072CP. you can see that the line conncetions on the board were cut aswell (left side by the TB cable going to the connector)

p.s.: am I alowed to add only one photo?

and one more to better see...

and the backside...
as you can see there has been an additional wire added if you look closely...

The right channel master module should be an exact copy of the left.

Well, it's clear someone messed up with the row of 22k resistors R29-34 and R129-134. In particular R29/30 and R129/130 have been rewired to reverse phase! And others have a different value than 22k. IMO no one in his right mind would do that.
I suggest you rewire this bunch of resistors the way God the designer intended first; then you may see if the problem still exists.

I can't see the added wire on the last picture; try to resize your picture and mark the place of this added wire; Windows Paint is your friend.

so this is on part of wiring on the back side...

and this is the other one with the cut traces...

so what do you think the intention of doing this could be? why cut traces and and why invert the faze and all that jazz? wich amps does this affect and in which stage?

everything else in the desk (channels, cableing and jack/xlr sockets as well as the metering looks original and untouched)

here is a photo with all the ICs.

I have check and the NE45532 are the same pinouts as the TL072 so probably not such a big problem but I would replace to the original if nesessery.

photo top nr 2

photo top nr 3

i kind of did a recording to see what's going on with the signal in protools.

it's a sine sweep wav track (20Hz - 20kHz) sent through a channel going to the master and recorded through all the outputs in 3 positions .

1. mono (panning in the middle)
2. panning hard Right
3. panning hard Left

noticed that when panned hard L or R the signal is stronger at least 3dB (but as of my knowledge this is normal for analog desks or am I wrong?)

you can see that C/R outs are the problem.

The crossed-over resistors and caps in the photo of reply #6 look to be error corrections of left-right signal paths and / or phase corrections. Studying the Master schematic & comparing to the PCB traces will give the answer. Although deeply involved in the 600 design, the Master PCB is not one of my layouts.

The date stamp of December 1984 ties in with changes that were done to the Master rear connector PCB at about that time. The guy who made the changes did not bother to check the PCB update records and as a result made incorrect changes. It's possible that these incorrect rear conn PCBs were ordered and that it was decided that it was easier to mod the Master PCB instead of modding (or scrapping) the rear-conn PCBs. This bit of R&D history coupled with (most of the) trace-cuts and component cross-overs relating to connector CN2 (which takes a 34-way ribbon cable to the rear conn PCB) suggests that bad rear conn PCBs were used and one ended up in your console.

+1 an unfortunate reality of console manufacturing is that you don't just discard production runs of PC boards.

Documentation is rarely completely up to date, on top of the lack of precision from hand drawn schematics.

Sometimes you just need to reverse engineer what is there. At least with stereo paths you have two chances.

JR

very very thankfull for your extensive input great people! I am very honored that actuall designers and people of skill are involved into helping uneducated people like me! I dont have too much of electician knowledge but i have done a lot of soldering, schematics reading , tracing problems and fixing them eventually, basicly learning by doing and this was one of the reasons why I bought this soundcraft for. apart from the burning love for music and production...

My first intentions were cleaning the sh... out of it and inspecting the errors and here we are, the fist and the only that I found. then when those are fixed and the desk works in full then I want to move on to modding the channels but only with recaping and giving them suggested different values for more performance. no IC changing... I dont know if the the 600 needs the starground mod as well but I will come to all of this later. but for now the only error was this master problem. I guess I have to find out if the backpannel output PCB might be in any damage or the faulty one like you suggest.

If the problem begins in the output PCB I belive putting the Master Module PCB back together to the original will be no problem.

but please could you inform me about how I can find out if the output PCB is wrong? and what to look for to identify it or even to find out any labeling that might point out the year of making.

I will backtrace the master module pcb and try to redraw the scematics aswell and post it here so you can see what was done.

also I will tak a photo of the back pannel output PCB in the next days.

again, I am very greatfull for your help! if it means anything to anyone, I am learing with every step!

thank you
Dario