Trouble with Dynacord powermate 1600 protection circuit

[babu123]

I have one Dynacord power amplifier powermate 1600. The problem with this is it power up and suddently stops and fan is not working .I checked the secondary voltage the volts -15 and +15 are present .but i herd the relay is cutting off .if any body has any idea please help me. Thanks

babu

[Jazz P Bass]

If the relay is dropping out, then the amp is going into 'protect mode'.
This is a powered mixer.
There are a few voltages that have to be present other than the + & - 15 Vdc.
For a starting point, I would suggest that you check the output transistors for a shorted condition.
Here is the schematic.

[babu123]

Dear Jazz P Bass,
thanks for your replay
I checked the power transistor its ok .I disconnected the +-Vcc rail then also it is the same.one thing I noticed is that the relay drive -24 volt at the collector of transistor Q811 that is BC337 Is not coming .but there is -vss at the emiter.that circuit is accociated with number of transistor and ends with TL074.all other places the voltage is present.I am confused where to start?
babu

[Jazz P Bass]

What is the base voltage of Q811?

[babu123]

Dear Bass,
the base voltage is -17v

[Jazz P Bass]

That circuit is giving me a headache!
At -17 Vdc, Q811 is barely on.
What is the collector voltage?
On the left, Time In, is marked -11Vdc.
Is that true?
The fact that the amp does turn on but turns off gives you a chance to see where the input signal is coming from to turn it off.

[babu123]

Dear bas it is true it is -10.5 when i measured.when the amplifier is on it should on the relay through the ptc resister .but it doesnot. I am also confused where to check

[Jazz P Bass]

Your reply is confusing.
In the original post you said that the amp relay turns on & then off.
Correct?
How long does it stay on?
At that point you should have 24 volts at the relay.
What is the collector voltage of Q811?

[Jazz P Bass]

when the amplifier is on it should on the relay through the ptc resister .

The relay 'bypasses' the PTC thermistor when the power supply is up & running.
A fault in the power amp section can turn the relay off.