Hertz HP1KD pre-amp problems??


2016-01-17 2:57 pm

I have problems with this HERTZ HP1KD, which has no audio output.
I got another technical assistance, they were not able to repair the exit.
I have repaired the output, thoroughly checking the driver board (replaced ir21844s, lm211, tl072 and 1.5uf capacitors (out of values) connected to pin 2 of 21844 and all 360LC.
I've checked all the voltages, + rail –rail, + 12v -12v, 3.3v, + 5v -5v. and they are all correct and present in the circuit.
I have injected 50Hz and 100Hz signal directly into pin 2 of tl072 using R76 to limit the function generator signal. Amplify well, with distortion, but at least amplify.
I think the problem is in the pre-amplification stage, I have reviewed everything, but not having a scheme, it is hard for me to locate the problem.
I have to say that resistance R158 is missing, I don't know its value…. I don't know if it could be the problem. I have tried changing resistances of different values: 200Kohm, 4.7Kohm and 1Kohm, without obtaining any positive results.

Has anyone had a similar problem?

Thank you.


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