DS18 H-K08

[caraudioguy2100]

Amp came in with blown power supply fets .

I replaced the fets and 2 driver ic’s didn’t replace the smd transistors yet .

When trying to power the amp up it shows no signs of life .

Any ideas ?

 

[Perry Babin]

Do you have both B+ and remote voltage on the headers of the driver board?

 

[caraudioguy2100]

Yes

 

[Perry Babin]

What's the DCV on all terminals of Q2?

 

[caraudioguy2100]

Base :0.00
Emitter:13.94
Collector:13.93

 

[Perry Babin]

Do you have 12v on pins 8, 11 and 12 of the 494?

 

[caraudioguy2100]

Yes

 

[Perry Babin]

What do you mean by 'no signs if life'?

Do you have a sawtooth waveform on the 494?

If so, post the voltage on all terminals of the 494.

 

[caraudioguy2100]

The amp will not power up . It won’t produce rail or regulated voltages .

TL494

Pin 1:6.51
Pin 2:2.55
Pin 3:4.67
Pin 4:3.88
Pin 5:1.63
Pin 6:3.10
Pin 7:0.00
Pin 8:13.65
Pin 9:0.00
Pin 10:0.00
Pin 11:13.65
Pin 12:13.65
Pin 13:4.99
Pin 14:4.99
Pin 15:4.99
Pin 16:0.00

 

[Perry Babin]

It appears to be in protect. What audio driver board does it use?

 

[caraudioguy2100]

It’s using this audio driver board

 

[Perry Babin]

The DC offset transistor often fails and causes this (driver board out). It's Q226 in many of the class D amps.

Do you see any voltage across any of the protect/power LEDs?

 

[caraudioguy2100]

It’s a digital display on the amp .

And yes the display lights up so there is voltage there

This is the transistor your talking about ?

 

[Perry Babin]

It's generally a through-hole part.

 

[caraudioguy2100]

I don’t see any through hole transistors on this board

 

[Perry Babin]

This is the group of components that you're looking for. I have noting on this amp, specifically so this is purely generic and may not apply to this amp.

 

[caraudioguy2100]

Can I lift the dc offset transistor to see if the amp will power up or will that cause problems

 

[Perry Babin]

Like any time that you're disabling any protection, you have to be careful. That said, the amp will operate normally without that transistor.

Did you find a circuit that is like the one in that diagram?

 

[caraudioguy2100]

Yes

I replaced Q226 and the amp powers up now .

The transistor I circled in an earlier post was actually Q225 .

Q226 sits to the right of it marked FR

So will put new outputs and a driver in the output section to see if the amp has anymore issues

 

[caraudioguy2100]

Amp powers up now and produces rail voltage

But the amp isn’t producing any regulated voltages .

Any ideas ?