Soundcraft TS-12 - SIP Channel 1 does not cut when another channel is solo'ed...

[stuartpre]

Hi thanks for reading,

My board is a Soundcraft TS-12 and has an issue.

Channel 1 does not cut, when another channel is solo'ed. It should, the other channels 2-24 do.
I have attached a pdf of the schematics.

Here is what I have found;

A jumper 'J1' should be installed to avoid (the optional 'do not cut my fx return' option), J1 is installed and continuity checked.

The schematic of i/o channel (1st page) middle bottom shows the 'Cut' button circuit... I noticed what I guessed to be a DC control voltage enters that circuit via connector 2 pin 19 'the CUT line from Automated L/H i/o' and connects directly to pin 1 of IC 14-A.

1. I tried replacing IC14 (A-D), no change ;(
2. I replace IC12 in the SOLO circuit but this had no change.

3. I measure a DC voltage at Connector 2 pin 19 on the smaller switch pcb (connector 2 is part of a interconnect system between main pcb and smaller switch pcb), I measured both the faulty module and a working module while soloing another track;

I noticed the presence of approx -8.6VDC present whilst un-Cut (no LED active) this signal was interrupted on the working channel when I solo'ed another channel (hence cutting the channel as it should), however the signal WAS NOT interrupted on the faulty channel when I solo'ed another channel! So this is a clue....but I am stuck

This DC voltage on connector 2 pin 19 the ' CUT line from Automated L/H i/o' DC voltage WAS  interrupted  on the faulty channel when I pressed the CUT button on the faulty channel itself. So is there something stopping the signal from the other channel? What is this something on the other channel? The SOLO circuit...is there a SOLO bus or something that interconnects between channels? Can anyone see it by looking at the schematic?

This is as far as I got. I suspect the Fet's TR5, TR6 in SOLO circuit, they look important and connected to CUT circuit but I am just guessing... I confess, I am at the limit of my knowledge, I did not study logic circuits ( i was too busy building GYRAF kits and recording) and I only know that a FET can be used as a switch...so this is why I suspect the fets, how do I test them? Do I de-solder them? Can I test them in circuit with my multimeter?

Thanks.

 

[ruffrecords]

Is each channel removable?  You could try swapping channels see if the fault goes with the channel.

Cheers

Ian

 

[stuartpre]

Yes, i've done that. It is as described above, see the discussion of differing voltage readings between the faulty channel and a working channel...

 

[ruffrecords]

I think you are right about it being the FET. The negative voltage will turn the FET off so it is high impedance. Removing it or taking it to zero will turn the FET on which is probably what is needed for cut. Hard to test a FET in situ. Can you try replacing it?

Cheers

Ian

 

[abbey road d enfer]

Since the CUT switch apparently does what it should, we can probably assume the FET's work as intended. Looks to me like the voltage from the Solo Sense Bus does not reach the daughter board.
I would suspect the connection (flat cable?) between mother and daughter.