Samson Servo 260 problems

[ew]

Greetings, I've got a Samson Servo 260 that when turned on, never comes out of protection mode & keeps one channel "clip" led on. Has anyone encountered this issue before? I've heard that the soft start relay on the Samson Servo's is often a cuprit, but I havent ever heard the symptoms of the relay circuit failing. Any info would be greatly appreciated!

 

[EchoWars]

Sounds like the output is stuck on a rail. Measure it and see what ya got.

 

[unclejed613]

just fixed a QSC amp that is very similar. had the same problem, except that the QSC doesn't have a relay..... clip LED in one channel was stuck on...... with signal applied, only the top half of the signal was there (hint, put a scope lead on the junction between the + and + half emitter resistors, as this is the speaker line before the relay).... one of the driver transistors had a broken emitter lead....

the samson amps are similar in design to QSC, Behringer, and Tapco amps.
check for dc offset and/or one half of the signal missing at the emitter resistor junction.... those are the main things that will latch the clip led with no signal........

 

[ew]

I looked over the board really closely & noticed that there were burns around Q111 & R124 as seen on the schematic on the attached link:

http://www.eserviceinfo.com/downloadsm/24098/Samson_550/260/170.html


Any ideas on what may have caused this destruction?

Thanks again!

 

[bobby2002]

Hi there,

I have the same symptoms with my servo 260, but there is no sign of scorch marks on my PCB. I realise that this is an old topic, but by any chance did you find the cause of your problem, and do you remember what it was?

thanks for any help you might be able to give

 

[jaycee]

ew's problem sounds like the amp was abused, the VI limiter formed by Q110/Q11 activated too much, and thus burnt out.

So, test the VI limiter transistors and the circuitry in that area, especially if you know the amp is likely to have been abused into clipping often.

 

[bobby2002]

Hi

thanks for the tip! I was putting off taking the pcb out because it looked at first as though you practically have to disassemble the whole unit to get it out, but you just take the back panel off and the pcb comes out with it. phew!

Q111 is indeed dead, and R127 has gone from 100 to 40 ohms. The casing of R127 is also bubbled from heat, which I did not notice before. Q108 has also been pretty hot. Proper testing to follow after lunch.

My knowledge comes unstuck a little here, but I am thinking that the DC offset (clip light on with no signal) would come from just one half of this stage burning out?

 

[ew]

I still havent gotten around to doing anything with that particular amp, although I have picked up two more dead ones since then. My main holdup has been the intention of picking up a 'scope, but still havent spent the $$. Thanks again everyone!