Hertz HDP1 - Thermal Protection LED ON but works fine

[jesgatt]

Hi,

I have an amplifier Hertz HDP1 and it is working fine. The only problem is that the TH LED is always ON. I checked the SW1 on the main pcb and it seems to be working fine. I followed the LED track and arrived till the board 37PW-HDP1-01 Rev:V0.0. I tested the transistor Q10 and it seems to be fine. The transistor is fed from R36 and D15 then from U3 (TL494C). Any hints what the problem might be? Thanks

 

[Perry Babin]

What's the DC voltage on pin 3 of the 494?

 

[jesgatt]

Hi, the voltage on pin 3 of the TL494C is 64.4mV (wrt to the ground of the battery). Thanks

 

[jesgatt]

Found the fault. One of the FETs (Q1) had a bad mica insulation and was shorting to the chassis. Replaced the mica and voila 🙂. thanks