Proel powered monitor repair help

[diydidi]

Hi There.
See attached schematic.
This speaker came in with no sound problem.
The only sound I hear is a ticking sound every 2 seconds from the woofer.
I checked the lines labeled CSD on the schematic. These are the mute lines that go to the TDA7294 and the IRS2092.
According to the TDA7294 datasheet, it needs a positive voltage over here to get it out of mute.
I confirmed this by removing D17 and feeding a +5V here. This takes the TDA out of mute, and the tweeter works without any ticking sounds like the woofer.
Weird thing is a can see a shift of DC level along with the ticking sound on my scope at pin 5 of IRS2092 woofer amp chip. I replaced this IC, no change.
My first question is, where does the TDA get the positive voltage from to take it out of mute? Q12 sinks to a negative -5,6V. Weird....
Maybe the IRS2092 sends a positive voltage out of its pin 5?? I don't understand...
Secondly, If I can get the tweeter amp to work, surely the power supply is fine?
I also replaced C51 and C56. I double checked all the voltages indicated on the schematic. The supply rails ±5,6V for the IRS2092 are there and clean.
Any suggestions .

[mozwell]

the CSD line according to the datasheet http://www.irf.com/product-info/data...ta/irs2092.pdf can just be a capacitor from pin 5 to pin 6, so pin 5 is a 100uA current source from an internal positive supply (6V internal zener), and when the capacitor charges & reaches approx 4V the chip goes out of shutdown. This will act as a soft start, and can also be for external shutdown by pulling pin 5 low

Check the positive supply to pin 1 of the IRS2092 chip (measure between pin 1 & pin2 0V) is this steady, also do the same for the negative supply between pin 2 0V and pin 6 -5.6V, is this steady,
The other circuits that may cause CSD to operate, are from the +30V supply & +52V supply, check these, are they steady, are there noise spikes (noise spikes on the 52V supply will cause CSD to operate.
Check the base of Q12, is this going high (+0.6V above the -5.6V supply), check the temperature sensor SW1, is this ok ?

To check if the whole amp is working, you could temporarily remove D18 or short B-E of Q12 and see if audio passes through the amp. If that is ok, then the problem is in the protection circuit around Q12 / Q13

[diydidi]

Thanx Mozwell.
Will have a look.

[xpert2k22]

Hi diydidi,
Sorry for the late enquiry, did you repaired this unit and which parts were faulty. I have the same fault in a unit. Appreciate if you would reply through my email shahid_ptv at yahoo dot com