Audison LR 604 XR Protection mode

[pippolonia]

Hi folks,

this year only question about Audison 🙂

Amps is a LR604 XR in protection mode.

Voltage on pin 10 of SG3525 is about 2,5 V (shutdown is up); if I disconnect the base of Q66 (forcing 0V in the shutdown pin of SG3525), switching supply start without any problem; outputs are +- 27 V, B+ current is 0,6 A ... I suppose they are OK.

Probably the fault is the circuit of safe mode, but it's a little bit difficult to understand with a double-face board without a circuit diagram 🙂

The PTC resistance is 100 Ohm, transistors, diodes, resistances around the power supply (tested with a multimeter) are fine ... I don't know what to do more !?!

Someone has an advise for me (or the circuit diagram) ?

Thanks

Giovanni

 

[pippolonia]

Hi,

a good conclusion for a little, but with good sound, amp.

The control of the state of output stage is made measuring the voltage on the emitter resistance. If value raise (probably a transistor blow), a BC550 (easy to find because it's connected to the others with a little red diode) set the amplifier condition as PROTECTION.

One of these BC550 was shorted ...

Happy week end

Giovanni

 

[Bertje]

Thanks for this onfo, nice amps!

 

[killerkeoki]

Thanks for the update, good to know.