Hifonics A3000.1D

[biscuitownz]

Hi all,

I have a hifonics alpha 3000.1D that goes directly into protect upon connection of remote power. Nothing on the board looks bad to the naked eye. All of the FETs measure OK.

This amp uses the TL494 for the power supply. I've checked all the SOT23-3 transistors near it and they all "measure" OK. Of course they could've failed in an open state.

I'll check the voltages going into the 2 opamps of the TL494 tomorrow. Does anyone have a schematic for this guy?

Attached some pictures of the amp.

 

[Perry Babin]

I don't have a diagram.

What's the part number on the IC U108(?) adjacent to the output driver IC?

 

[biscuitownz]

It is 74hc02d.

Attached better picture for that section

 

[Perry Babin]

Does it have any shorted output transistors?

 

[biscuitownz]

None that I can find. PS FETs measure fine as well.

 

[Perry Babin]

Copy and paste the following list and fill in the blanks. If there is no blank space after the colon, add one between the colon and the numbers you enter. It makes it much easier to read.

DCV on all terminals of the TL494.

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:

 

[biscuitownz]

Pin 1: 2.65V
Pin 2: 4.47V
Pin 3: 4.64V
Pin 4: 4.17V
Pin 5: 1.46V
Pin 6: 3.70V
Pin 7: 0V
Pin 8: 14.03V
Pin 9: 0V
Pin 10: 0V
Pin 11: 14.03V
Pin 12: 13.28V
Pin 13: 5.03V
Pin 14: 5.03V
Pin 15: 5.03V
Pin 16: 10.09V

 

[Perry Babin]

Can you post a good quality photo of the components near the TL494?

 

[biscuitownz]

Here you go. Let me know if you need another angle.

 

[Perry Babin]

IUf you lift Q604, does the amp power up?

Be careful, this should disable part of the protection circuit.

 

[biscuitownz]

It powers with Q604 removed!

I see rail-rail oscillation before the LC filter as well. But there doesn't seem to be any modulation when I input audio. I can trace that tomorrow but what would cause it to be in protect like that?

 

[Perry Babin]

Do you have supply voltage across the PS pins of U108?

IS there a burned component just behind the RCA jacks?

 

[biscuitownz]

I'll have to check the supply voltage tomorrow. But there are two components that are burnt right behind the RCA jacks. Seems to be coming directly from the signal trace of the RCA as well, makes sense why signal wasn't getting through. Any idea what part they are?

 

[Perry Babin]

Likely something like this. You can bypass them, for now.

 

[Perry Babin]

This amp has some similarities with yours (different/missing output stage).
https://www.diyaudio.com/community/threads/ir2010-burnt-traces.402358/post-7477196

 

[biscuitownz]

I removed the filter after the RCAs and jumpered them. The amp plays music fine, I can drive it into clipping and the waveform looks clean all the way up.

It seems that the issue is now isolated to the protection circuit on the TL494.

 

[Perry Babin]

Reconnect the protection circuit to see if it still has a problem now that you jumped the inductors.

 

[biscuitownz]

I did reinstall Q604 and the protection light comes on.

 

[Perry Babin]

Do you see a Q608, Q609 and D606?

 

[biscuitownz]

Yes, they're right behind the speaker terminals and the relay.