Hi guys,
I'm working on a GZHA 4120X amplifier. I fully restored the power supply section, but now I'm running into trouble with the filter section.
The green 'on' light is not working and there is no audio signal on the speaker terminals. While the power supply section works excellent and the output fets recieve their rail voltage.
The audio signal from all 4 channels don't reach the potentiometers and the switches and seems to stop directly at 2 NJM4558L op-amps (1 NJM4558L per 2 channels)
They don't seem to amplificate the music signal.
NJM4558L DC values
Pin 1: 0.607v (I expect the output to be here)
Pin 2: 0.607v
Pin 3: 1.457v (audio signal from RCA's. Music signal is present)
Pin 4: -13.15v
Pin 5: 1.457v (audio signal from RCA's. Music signal is present)
Pin 6: 0.605v
Pin 7: 0.606v (I expect the output to be here)
Pin 8: 0.071v
Anybody got a clue?
I'm working on a GZHA 4120X amplifier. I fully restored the power supply section, but now I'm running into trouble with the filter section.
The green 'on' light is not working and there is no audio signal on the speaker terminals. While the power supply section works excellent and the output fets recieve their rail voltage.
The audio signal from all 4 channels don't reach the potentiometers and the switches and seems to stop directly at 2 NJM4558L op-amps (1 NJM4558L per 2 channels)
They don't seem to amplificate the music signal.
NJM4558L DC values
Pin 1: 0.607v (I expect the output to be here)
Pin 2: 0.607v
Pin 3: 1.457v (audio signal from RCA's. Music signal is present)
Pin 4: -13.15v
Pin 5: 1.457v (audio signal from RCA's. Music signal is present)
Pin 6: 0.605v
Pin 7: 0.606v (I expect the output to be here)
Pin 8: 0.071v
Anybody got a clue?
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Seems to be that the positive regulated voltage (+15v to pin 8 of the op amp) are lost!
From your photo, I see 2 things:
1) the regulated voltages (+/- 15v) are generated through 2 linear regulators (usually, transistors), try to check that they are good.
Check all the components that I have circled in yellow ..
2) what material is the one circled in red? I don't think the producer company used that tape as a thermally conductive pad, it must be replaced immediately, as it does not conduct thermally and will very soon cause the breakdown of the active components that heat (output transistors).
You can use capton tape or heat conductive rubber or silicone pad.
From your photo, I see 2 things:
1) the regulated voltages (+/- 15v) are generated through 2 linear regulators (usually, transistors), try to check that they are good.
Check all the components that I have circled in yellow ..
2) what material is the one circled in red? I don't think the producer company used that tape as a thermally conductive pad, it must be replaced immediately, as it does not conduct thermally and will very soon cause the breakdown of the active components that heat (output transistors).
You can use capton tape or heat conductive rubber or silicone pad.
Attachments
Last edited:
Problem is fixed, there was a broken trace which prevented the rail voltage to acces the +15v regulator.
Amplifier is fully working now, included the green light.
I'm not sure what material the black "tape" is. Seems like a kind of rubber with a kind of woven material inside.
There was worked on the amp before, which was done very bad. Also probably the reason why the amp died again.
I have replaced it with some proper material, due tue the fact that it already broke open and made contact with the housing. Thanks for the sharp eyes 🙂, I appreciate it.
Amplifier is fully working now, included the green light.
I'm not sure what material the black "tape" is. Seems like a kind of rubber with a kind of woven material inside.
There was worked on the amp before, which was done very bad. Also probably the reason why the amp died again.
I have replaced it with some proper material, due tue the fact that it already broke open and made contact with the housing. Thanks for the sharp eyes 🙂, I appreciate it.
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