Kicker ZX100.2

[Dr Zeus]

I cant get this amp to power up properly. Amp produces only +-1.8vDC rail. The TL494 has voltages as follows:

TL494
Pin 1: 0.456
Pin 2: 5.03
Pin 3: 4.69
Pin 4: 0.037
Pin 5: 1.508
Pin 6: 3.451
Pin 7: 0.005
Pin 8: 8.66
Pin 9: 0.023
Pin 10: 0.023
Pin 11: 8.67
Pin 12: 13.65
Pin 13/14/15: 5.03
Pin 16: 5.05

Q1 has 13.65vDC on all three legs

[Perry Babin]

The IC appears to be working correctly. Pin 16 being higher than pin 15 is causing the problem. I don't have any information on this amp (not even photos) so you'll have to trace it back to see what's driving it high. If you can't figure it out, post a high resolution image of the area around the 494.

[Dr Zeus]

Hmm.. Tracing through some things, there are quite a few directions pin 16 takes. I found another thread on this amp that had an opposite problem where the amp would not turn off due to a bad Q2, 2n4401 transistor: kicker zx100.2

Q2
Leg 1: 0.005
Leg 2: 0.614
Leg 3: 0.050

The thing is though, when I remove REM the amp turns off correctly.

In this photo, 494's pin 16 goes to R63 and R29.



And this photo pin 16 is directly in the middle of the picture.

[Perry Babin]

Post the DC voltage on the 4558.

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:

[Dr Zeus]

4558

Pin 1: 1.481
Pin 2: 5.04
Pin 3: 0.804
Pin 4: 0.003
Pin 5: 3.743
Pin 6: 7.29
Pin 7: 1.434
Pin 8: 8.31

[Perry Babin]

OK, it doesn't appear to be driven by that op-amp. What if you pull the TO-92 transistor near the standing resistor (assuming it's also connected to R29)? Be careful, it may draw excessive current.

[Dr Zeus]

Thats a 2N4403 at Q15 and its connected to R63 (Just next to R29) which is also comming off of 494's pin 16. Off the board the 2N4403 checked out OK.

With Q15 removed, the amp powers up but I'm affraid the power supply fets IRFZ46N w/ 100ohm gates get slightly warm to the touch after about 10 seconds. The gate waveform is a little low measuring a ~+7v square wave. The waveform on Legs 1&3 of the rectifiers is an Un-Regulated +-20v square wave. The rail voltage is +-20vDC. The opamps are getting +-15vDC.

With Q15 removed, the 494 measures as follows:

TL494
Pin 1: 5.03
Pin 2: 5.03
Pin 3: 1.924
Pin 4: 3v but then drops to 0v
Pin 5: 1.497
Pin 6: 3.424
Pin 7: 0
Pin 8: 8.56
Pin 9: 2.3
Pin 10: 2.3
Pin 11: 8.47
Pin 12: 13.65
Pin 13/14/15: 5.03
Pin 16: 2.204

[Dr Zeus]

The amp is able to produce clean audio on both channels

The power LED is RED indicating amp is still operating in protection. A green LED works with the fluke 10 meter.

[Dr Zeus]

Tracing around Q15, I find it strange that legs 1&2 are connected together through R39 (20k) and R61 (1k) in series while leg 2 is also connected to R62 and JR2. Q7 which is a 2N4401 may be suspect as its connected to JR2 but it is measuring just fine on the pcb.

[Dr Zeus]

Just found something wierd. it looks like a manufactoring defect where this 25v 2200uf cap was not connected to the PCB by more than a big glob of glue. The legs we not even going through the PCB.