HiFi Power Amplifier High Temperature Problems

[Filipe Zadeira]

Hello
i do have a hifi amplifier

two compoennet is geting hot very fast, as soon as i start the amplifier

On transistor had failed
I changed it , but as soon you start the power , it is getting hot verry

on the schema it is the Q5 ans also R10 is getting hot

Any idee , i did have problem to understand
R16 ,D5 look ok
i did have 15volt on U1 pin 15
on my bord R42,R43 and Q7 is missing or shorted somehow

see the file here


You can find the full service manual just google
labgruppen_fp2400q_v02_amplifier_service_manual


thank you

 

[D.A.(Tony)Stewart]

DO you have all the required test equipment including variac, isolation transformer and scope.?

This suggests the supply voltage is too high for the current sink or the sink is supplying too much current. Check across D4 = 5.6V (zener) and across R16 (180Ohm) is 4.9V (18mA) then R10 (4k7) is 85V (1.5W /7W)

 

[Filipe Zadeira]

Hello
unfortunaltly no variac, isolation transformer and scope, just a multimeter !

i do have on
R10 125v i am in Europe 220V
R16 4.9V
and zener is 5.6

 

[D.A.(Tony)Stewart]

then Q5 & R10 needs ventilation as it is only using 50% of 7W of rated power. (WW)

 

[Filipe Zadeira]

then Q5 & R10 needs ventilation as it is only using 50% of 7W of rated power. (WW)

Ok thank you

 

[FvM]

It hasn't been explicitely stated in the thread, but I assume that the power supply was working correctly before. If so, you are possibly looking in the wrong place. R10/Q5 seem to be part of a startup circuit that shouldn't dissipate much power in normal operation. Instead the controller voltage supply will be fed from a transformer winding.

So the underlying problem might be:
- inverter doesn't start
- normal supply path is interrupted
- controller supply voltage is shorted somehow