Trace Elliot 715x Combo Woes!!

[HIWATT69]

Hi folks.
Posting in on behalf of our bass player.When playing through his amp with the built in 8ohm speaker after a couple of minutes it cuts out and the mute light/circuit comes on.
Speaker has been checked and is fine.
He's discovered if he adds an extension speaker(speakon connection,4x10 8 ohms) along with the internal speaker the amp works fine but using either the external speaker(speakon connection) on it's own or the internal speaker(Jack) on it's own the amp cuts out and the mute circuit/light kicks in?
The only thing I can think of is when running both it will be running at 4ohms?
He put it in for repair and was told it would need a new OT but surely a shorted OT would give no output at all?
Also was told it would need a new PCB but not sure why if it's the OT?
Has anyone experienced anything similar with this amp?Could it be the mute circuit that's dodgy?
Any help would be much appreciated as it's being written off as an uneconomical repair and he's not long bought the amp.Thanks in advance.

 

[Downunderwonder]

Not familiar with the model. What year?

 

[HIWATT69]

I'm not sure what year exactly but it's a 715x GP7

 

[delta7fred]

I'm not sure what year exactly but it's a 715x GP7

Time for a new amp tech, that model doesn't have an OT but is a solid state power amplifier, either bi-polar or mosfet.

The bi-polar amps had a nasty habit of going unstable (and self combusting) because the ground connection to the output amplifier board goes high resistance due to a star washer being missed off at manufacture.

Mine did this and took the speaker with it, the PCB was burned beyond economical repair so was replaced by the later Mosfet amplifier and I need a new speaker. It started by being intermittent and rapidly went downhill, I would advise against powering it up until you check foe the star washer.

See also this thread (Older) Trace Elliot tuning ports?

 

[HIWATT69]

Time for a new amp tech, that model doesn't have an OT but is a solid state power amplifier, either bi-polar or mosfet.

The bi-polar amps had a nasty habit of going unstable (and self combusting) because the ground connection to the output amplifier board goes high resistance due to a star washer being missed off at manufacture.

Mine did this and took the speaker with it, the PCB was burned beyond economical repair so was replaced by the later Mosfet amplifier and I need a new speaker. It started by being intermittent and rapidly went downhill, I would advise against powering it up until you check foe the star washer.

See also this thread (Older) Trace Elliot tuning ports?

Thanks for your reply.
I am getting the information second hand but he did mention an output transformer and having to replace the PCB which is why I was confused as the PCB is obviously completely separate(I'm more familiar with tube amps)
As far as I know there is no visable damage to the PCB.
Any idea why it would work with both speakers being used but cut out only the one being used?

 

[delta7fred]

Any idea why it would work with both speakers being used but cut out only the one being used?

Not really, faults like that usually point to a bad connection that makes or doesn't under different conditions.

The muting circuit uses a push button switch so that is a bit of a puzzler why the light should come on when the amp cuts out.

Disclaimer - Fault finding over the net is an order of magnitude more difficult than having the item on your bench.