Hifonics Thor X not powering on

[Dr Zeus]

In trying to fix this amp, I shorted R116 and R216 to the chassis and now it wont power up. While it was shorted, the amp actually played fine but would not turn off. It got kind of hot, but not hot enough to turn on protection or pop any transistors. I see a lot of amps posted in this state with TL494CN values. I only see 12vDC at the front of the coil and 6vDC on the back. No AC at transformer coil.

TL494CN

1: 0.772
2: 5.02
3: 4.73
4: 0.215
5: 1.411
6: 3.388
7: 0
8: 12.27
9: 0
10: 0
11: 12.27
12: 12.26
13: 4.97
14: 4.96
15: 4.97
16: 11.46

Is this TL494CN working right?

[Perry Babin]

Can you post photos of the area around the 494 and the area around the resistors you shorted.

[Dr Zeus]

This is unfortunately my handy work. The original R116 and R216 looked burnt so I replaced them. I did this all about a month ago; before I really started really learning how to apply myself in fixing amps. You can see I used two wire-wound 2.7 Ohm 5w resistors in place what should have been 2.7 ohm 1w resistors. Then, after soldering these in I forgot to clip the excess on the back and all 4 leads shorted to the chassis. Amazingly the amp actually played in this state for about 30 minutes until I realized it would not power off. The TL494CN is just near these resistors.



Starting with the 2 large pads directly in the center of this photo; R116 and R216 leads were left uncut and shorted. The small white wire is connected to Pin7 of the TL494CN :

[Perry Babin]

Those aren't causing the problem. If the leads only shorted to the chassis, the outputs are likely the only components damaged. Have you checked the outputs again?

If the leads were long and folded back onto the board and shorted to other components, that could have caused damage to other components. Is there an 8 pin op-amp on the board near the 494?

Follow the traces from pin 16 back from the IC. It goes to the hybrid module (what's the number ON the module)?

Where does the trace go from there?

[Dr Zeus]

Just checked the outputs. Nothings shorted, and diode check seems fine on all fet and output transistors.

I dont know if the leads folded back - I cant remember exactly. When I found them that way I was able to clip them without taking the PCB off the sync so i could not tell.

Pin16 is splitting in a few different directions. First is to the resistor network (You can see that in both pictures). Second is to some glas diodes which check out fine. From the diodes the trace connects to Pin1 of the 14 pin BA10324A which is quad ground sense opAmp. On the top of the PCB is written LATCH. I think this module also does Lamps and thermal operation. Is that the hybrid module?

http://www.datasheetcatalog.org/data.../233206_DS.pdf

[Dr Zeus]

The BA10324A's voltage pins (4 & 11) measure 0v from the amp's general ground.

[Perry Babin]

The module has a circuit board designation of TLPSU (long SIP component, covered in black epoxy).

The latch is used to keep the power supply off after a transient fault (such as shorted outputs, etc.).

Can you post a photo showing all of the power supply end of the amp?

[Perry Babin]

If the latch output (pin 14 on the 324) is driving pin 16, it's likely that the 324 had voltage when you read 11.46v on pin 16 of the494. Re-check your setup. If you still have 11+v on 1 and there is no voltage on pin 4, the diode may be isolating the 324 from the 494.

[Dr Zeus]

Its TLPSU-96 then. You can see it in the first 2 photos I've posted. Pin16 of the 494 is hooked into the first (Top view, left most) pin of the TLPSU.

They're not too pretty - turned a bit green but not from my doing. The amp must have been pushed really hard a long time ago. My resistor shorts did NOT cause the traces near the Fets to turn green. Continuity seems fine in all power supply areas.

I left the 494 in focus in both of these photos:

[Dr Zeus]

If the latch output (pin 14 on the 324) is driving pin 16, it's likely that the 324 had voltage when you read 11.46v on pin 16 of the494. Re-check your setup. If you still have 11+v on 1 and there is no voltage on pin 4, the diode may be isolating the 324 from the 494.

I cant seem to trace 324's pin 14 to the 494's pin 16, but I think I found the problem anyways.

Seems D2 is blocking 12v from hitting the 324's pin 1. I have D2 pictured a few times above, and on the left side I measure 11.8v. On the right side I measure .7v. D1 is in the same connecting trace and it is NOT blocking traffic. 12v on both sides.

Replace D2? I've got a spare 1w Zener on hand, but the package says its rated for 5v...