Setton RS-440 protection indicator

[SorenBx]

Hello
I have a problem with my Setton RS-440: Protection is on all of the time so there is no more sound coming out. Any idea why and what I should do ?
Best regards
Søren

 

[peterpl]

Hi,
I don't want to open another topic as I have the same problem with my Setton AS 3300.
I have replaced all electrolytic caps and the speaker relay plus the ICs ( I have S-80W) were replaced as I had a pair of spare ones.
Everything was fine and Setton played for about an hour and then a protection circuit was activated, lamp on point 14 is on and I don't know what to do.
I attach a schematic - on point 7 there is +44V, point 8 -44V and point 9 +20V, caps C31 and C32 are bipolars and they were replaced as well.
Before I was generally checked all transistors in protection circuit (without taking them out) and they seemed OK.
Any suggestion is welcome.
Best regards
Peter

 

[llwhtt]

First check for DCV on Pin 4 on both of the S60W power ICs, should be 0VDC or close to it.

Craig

 

[peterpl]

There is -32mV on the right hybryd and -50mV on the left.

I also wonder on the role of that small PCB 009 which is connected through pin 10 and when activated goes to the ground through transistor Q1.
When I was checking if relay works ( before final assembly) I just connected voltage to pins 7,8,9 plus grunding but I connected nothing to pin 10 and relay worked.

 

[peterpl]

Guys, please help
I am not sure whether under normal circumstances (no dc offset detected) transistors Q5 and Q6 should be ON or OFF?
Now they're off, below are measurings:
Q5 and Q6
Base -32mV -49mV
Col. +43.3 V both
Em. -43mV -59mV
 Q11
B 43.3V
C 2.5V
E 43.3V
 Q14
B 631mV
C 80mV
E 13mV
 Q15
B 80mV
C 43.5V
E -21mV

 

[llwhtt]

I have most of the protection circuit figured out, just need to figure out the last of it, patience.

Craig

 

[peterpl]

Thanks, maybe I should measure BE and BC voltage if each transistor, I will do that tomorrow. Each transistor passes a diode test but it must be a failure somewhere.
Attached there is a description of protective circuit in Setton RS440 very similar with clipping detection added

 

[peterpl]

I have measured VBE and VBC for each transistor:
Q5 VBE 10mV
VCE 43,3V
Q6 10mV
43,3V
Q11 -15mV
40,7V
Q14 618mV
75 mV
Q15 38mV
43V
I think both Q5 and Q6 are off
The VBE on Q11 is floating, I will replace that transistor and will check again
Any thoughts are much appreciated

 

[peterpl]

Problem solved !
The reason was faulty Q11 leaking current threfore had 2.5V on colector.
I have replaced it with KSA992.
To summarize: on normal operation Q5 and Q6 are off thus Q11 and Q14 are also off so only Q15 Is on.
DC detection activates Q5 or Q6 so they activate Q11 and Q14 which "steals" current from base of Q15.

 

[llwhtt]

I knew Q15 had to be ON as it controls the relay and the OPERATE lamp. I got stuck figuring out the initial time delay which I think is Q14 which turns off when the circuit times out. Good to see you figured it out.

Craig