Blackstar HT20R MKII No sound

[Mars Amp Repair]

Hello folks,
I believe most know that these HT models require a speaker & input to be plugged in, in order to release the bias muting and take the power tubes out of cut-off.
I found that this model has a unique schematic from the others (find attached).
In this case, the transistor that works off of the input jack, TR26, was leaky causing the transistor to not conduct, thereby keeping the PA_ON_L signal to TR32 from activating the bias adjust control, thereby keeping the power stage in cut-off.
TR26 and TR27 work in conjunction to release the bias muting. They are small SMD parts located about 1 1/2" behind the input jack.
Find schemo attached.
glen

[glebert]

I worked on these a couple years ago, here was the hack that we came up with to get it working. Easier than trying to replace SMD transistors for a largely unnecessary feature like the input jack mute.

https://music-electronics-forum.com/...probably/page2

[Mars Amp Repair]

I worked on these a couple years ago, here was the hack that we came up with to get it working. Easier than trying to replace SMD transistors for a largely unnecessary feature like the input jack mute.

https://music-electronics-forum.com/...probably/page2

Glebert,
that link took me to an explanation of how the muting ckt works, but no hacks to circumvent it. I could have done that, but it is a store stock dealer item and I tend to not modify units that fall into that category. Since the xistor most likely went out as a result of a static zap from the input jack, I would either add a zener diode to hopefully limit that if the issue seemed to reoccur.

Replacing the SMD in this amp wasn't really a big issue with a hot air device.
Thanx for the info. Glen

[glebert]

Glebert,
that link took me to an explanation of how the muting ckt works, but no hacks to circumvent it. I could have done that, but it is a store stock dealer item and I tend to not modify units that fall into that category. Since the xistor most likely went out as a result of a static zap from the input jack, I would either add a zener diode to hopefully limit that if the issue seemed to reoccur.

Replacing the SMD in this amp wasn't really a big issue with a hot air device.
Thanx for the info. Glen

Sorry, the hack was on page 1 of the thread, the link was to page 2. See post #10.

https://music-electronics-forum.com/...oblem-probably

[Mars Amp Repair]

Solution to keep tr26 turned on would be by shorting its collector to ground. That way if TR27 were open, it would not affect the bypass. Thanx for the redirection. Glen