Boss CS-3 repair / schematic explaination needed

[sonic66]

This is a follow up to my earlier post, to do with boss cs-3 Compression sustainer.


The attack function doesn't appear to work - due to a poorly done mod attempt. 
i thought i'd fixed it but  i hadn't.


What seems to bee happening is that there is no noticeable effect unless the sustain  is turned up, and increases as its turned.

ok what could i have fried? i assume fried by over heating will mean open circuit , is that correct?



from the following circuit diagram...



1.  i cannot have fried ic4a  as the sustain control works.....

2 .  posssible ic 3 got fried , thouht i didn't  solder on a trace attached direcly to this chip ( dbx c1252h2 ja 6054 , its an old mij cs-3)

3. i did colder on a trace to ic1 but i still get normal levels of signal through,  from the circuit it  wouldn't seem to be obvious

4  im wondering if q8 or q7 might be damaged, though  again i didn't solder  directly to them.




I tried to replace the caps c6 1uf and c4 1uf with film caps....

c4 goes to pin 1 of ic3 via a 33k resistor, c4 goes to pin 3 of ic4a via 100k resistor.




any one can explain how this circuit works and what migh cause loss of attack control ?




Thanks


.... http://www.dirk-hendrik.com/images/cs3.gif

[Rob Strand]

If you ask me that schematic has an error which prevents the compression part of the compressor working.  Someone brought this up a long time ago.


Q6 and Q8 are the output of the rectifier which makes the gain control circuit function as a (feedback type) compressor.  You see, the output of IC4b is hard wired to the gain control input at the gate of the Q7. IC4B has a low output impedance so no matter what current flows in the collectors of Q6 and Q8 they cannot change the voltage at Q4B's output.   The result is the sustain pot affects the gain and the compressor doesn't function as a compessor - all you have is a complicated volume control.

If IC4b was an open collector output then it should work but from what I remember that IC is not open collector.

One possibility is the output of IC4B needs to connect to the node formed by, Q6 collector, Q8 collector, and Q7 gate etc, using a diode.  The anode connects to Q6 collector and the cathode connects to IC4B's output, pin 7 and pin 8 remain connected.   There may be other ways to connect this.

The point is the behaviour you are seeing is what I see from the schematic, there's probably nothing wrong with your stuff it's the schematic.   If you have a real board then I'd suggest trying to trace out that area and reconstructing the real schematic.  Also, you mods may have worked if you followed the real schematic.

[sonic66]

does anyone have a correct schematic ?

i have problem i described is on the  cs-3  that i have .... attempted to mod

I didn't use this cshematic for the mods i did....

i thought it  was correct .... and refered to it for  explaination