TDA7294 AMP Thermal cut out. HARTKE AC5

[ziggy007]

Ok. I’ve isolated it to a rising voltage on the input to Q4 base. Rising from 0 to .620v where Q4 turns on and mutes.
I gotta say I’m not getting why. Hopefully I’m just a dumbarse and it’s captain obvious that I’m not seeing but I’m not seeing why. No diff to input from the phone sense. It stays at 0v. So it’s obv c86 or D23 or is it Q4? I’ll shotgun replace them tomorrow arvo but would love to understand better. Cheers Gav

[J M Fahey]

I’m not seeing but I’m not seeing why. No diff to input from the phone sense.

We can´t see it either because YOU HAVE NOT POSTED THE FULL SCHEMATIC AS ASKED TO SO WE CAN NOT SEE THE PHONE SENSE ACTIVATOR.

[ziggy007]

Ok sorry, no need to yell at me! Lol. Sound like my ex wife. 😆(I posted the relevant schematic previously).
The phone sense input stays at 0v when the fault is active. (Unless phone jack inserted) The 15v rail stays steady.

[nickb]

Can you post the actual file rather than what looks to be a screen shot please?

[Enzo]

OK, so the phone jack thing stays grounded, the only other path for the voltage is through R149, which points to the cap and diode. Yes or the transistor itself. So replace the two small parts and see.

[J M Fahey]

Ok sorry, no need to yell at me! Lol. Sound like my ex wife. ��(I posted the relevant schematic previously).
The phone sense input stays at 0v when the fault is active. (Unless phone jack inserted) The 15v rail stays steady.

Well, I *still* don´t see it.
*Still* don´t see the full schematic.
*Still* don´t know what´s at the other end of JP16
Geting data from you, to help you, is like pulling teeth.

[ziggy007]

ACR5 schematic_V1.5 - 2016 1122.pdf
Hope this works. Sorry I thought the screenshots were ok. (Hard to figure out via the iPad)
I’ve unplugged the phone jack and confirmed that line stays at zero.
I will change the 3 sus components this arvo, no probs. Wondering why, how/why this part was of the circuit is slowly building voltage.
Cheers. Much Appreciate all the help.

[ziggy007]

Traced the fault to D23 in the mute cct. Removed it tests ok but in circuit it was allowing the 3 second start up mute circuit voltage to to slowly rise and bias on Q4. A lot of lessons learnt. Thank you all for your help! Cheers Gav.