tl494 in protect

[Hexhclass]

Hi all

Trying to find the problem with this DHD NTX3107 amp.The amp goes into protect as soon as i power it on.If i pull the diode that is connected to pin one of the 494 it will power up ok and produce rail voltage.

#TL494
pin1: 12.15
pin2: 2.47
pin3: 4.72
pin4: 4.60
pin5: 1.47
pin6: 3.62
pin7: 0.00
pin8: 13.64
pin9: 0.00
pin10: 0.00
pin11: 13.64
pin12: 13.64
pin13; 4.97
pin14: 4.97
pin15: 4.78
pin16; 0.06

PS op amp
#4558
pin1: 12.79
pin2: 7.82
pin3: 2.90
pin4: 0.00
pin5: 2.54
pin6: 4.97
pin7: 12.78
pin8: 13.14

 

[Perry Babin]

Does it also produce clean audio?

Can you post a photo of the board?

 

[Hexhclass]

I did not test it for audio.When i pulled the diode i think i had something else out of the circuit because now when i pull that same diode it stays in protect.Maybe something went bad because i pull it.

 

[Perry Babin]

The op-amp appears to be defective.

 

[Hexhclass]

I replace the op-amp.Now if i pull diode location D8 the amp will power up and play good audio.
The diode is connected to the center leg of a C945 transistor through a 47k resistor and the other end goes to the audio section through two 1k resistor.Each of the resistors connect directly to a transistor in the audio section.

 

[Perry Babin]

Reinstall the diode and lift the two 1k resistors (only one at a time) to see which channel is causing the shutdown..

 

[Hexhclass]

I lift the 1k resistors one at a time but amp stayed in protect and is trying to come out of protect about every 20 second..The voltage at pin one on the 494 is12.14v.

 

[Perry Babin]

If you remove the C945 transistor, does it power up normally?

 

[Hexhclass]

Am not sure what in happening.I install the last 1k resistor i had pull.
Now amp power up normal.I don't no if the problem will come back but it looks like the main problem was the op-amp.