HT-5 2009 build Silent treatment

[Doctor49]

I have a 2009 build HT-5 head that just did the classic crackling log fire and no guitar from the speakers and perfectly reproduced output on both channels from the Emulated Output.
So I opened up and there is no sign of any overheating of any components on the topside of the PCB. I didnt check the back side yet.
The PCB layout is also different from the later versions in that the TR2 and TR3 are nowhere near the R38 R39, R10 resistors. In the overheating cases they are either side of the resistor pair.
So.....this is different from the usual R38, R39, TR 2, TR 3, R10 burned out issue, because in this case the crackling continues from the speakers even when the Emulated Output jack is in place and headphones are working.

Does that mean that there is something wrong in the emulation circuitry that turns off TR5 and the power stage when the headphone jack is inserted, otherwise there is no way for the crackling to continue through the speakers.....is there?

i'm fishing here....any ideas?

BTW I'm in Bangkok so the sole Blackstar dealers have a long throw back to UK for repairs

[thephantum]

I don't believe the power stage gets turned off when you plug into the EO. Rather, the input signal to the power stage gets cut (on later models, you have to put the amp in standby to use the EO silently). So the power stage is on with no input signal.

Have you tried changing the output tube?

[Doctor49]

Thanks - that looks like being the next step..............

I am thinking about this first though -
http://www.thegearpage.net/board/showth ... ?t=1259222
But some thoughts--- First, the headphone jack. You say the sound is correct here, but not through the speakers, so anything BEFORE the jack is likely OK. The jack itself might be flaky though (common). It's got a switch it in that turns on TR5 when nothing is plugged into the headphones. (via R94). To see if this is the problem, you can jump from R94 to GND and turn on the amp. If it works, voila you found the problem! (Jump the side of R94 that connects to the jack, NOT the side that goes to TR5)

[Doctor49]

No apparent fault anywhere else, so its back to the dealers today. They have EH power tubes and an alternative to the Sovtek preamp tube in stock. They are not convinced its the Power Tube, so let them play around and see what it really is!

[Doctor49]

Well its not the tubes.
Now they are tracing the signal and checking components................

zzzzt......zzzt....
zzzzt......zzzzt.....

[Doctor49]

They say its the output transformer, they ordered a replacement from the factory which I guess means Korea (who knows how long to wait ) so lets see.