I'm restoring a QX-949 (not A) which was not coming out of protection when I got it.
I found DC on Pin39 of one of the power amp boards, and rebuilt the entire Power Amp assy. Replaced all small transistors, caps, diodes, and trimmers. Outputs were fine, they got new micas and Dow 340. It now comes out of protection with no issues, and overall the unit is working fine.
I cleaned every switch and pot at least once. I cleaned the relay.
BUT, here is the problem: I am getting what I describe as wind noise/static out of both channels when Phono 1 or Phono 2 are selected. This is more than just hiss, and not hum. It comes and goes, but is there more than not. Only on phono, dead quiet on AUX.
I know the usual culprits for this kind of noise are the notorious 2SC1312 and 2SA725. Especially on the EQ board. I have rebuilt the following boards, one at a time: Power Amp, Control Amp, Power Supply, EQ assy, Matrix Assy, and Decoder circuit. "Rebuild" in this case means replacing all small transistors: 2SC1312 (or 2SC1000, 1344) with KSC1345, and all 2SA763 with KSA992 (this unit had 763s, not 725s) but I replaced them any way. All electrolytic caps on all boards were replaced with either Nichicon UPW, UKL, UFG, Panasonic FC (power supply), or WIMA MKS2 for the small values.
I have checked solder joints, wiring (jiggled all at the selector switches), and ground points, but the phono noise is still there.
Noise is there with nothing connected to the phono jacks, with shorting plugs in the phono jacks, or a turntable connected, does not matter.
To try to narrow down the source, I connected the output of the EQ board (pins 14 and 17) to the aux input of my bench amp, and to my scope, and the noise it not there. So this tells me the noise is coming from downstream of the EQ. Once I determined it was not the EQ I went ahead and rebuilt the Matrix, board and Decoder board. No improvement.
The noise is present regardless of setting of the MODE switch (2CH, RM, SQ).
The only boards that have not been touched (yet) are the Protection board, the Sub-Channel (SQ) circuit, and the tuner board.
Anybody got any suggestions?
I found DC on Pin39 of one of the power amp boards, and rebuilt the entire Power Amp assy. Replaced all small transistors, caps, diodes, and trimmers. Outputs were fine, they got new micas and Dow 340. It now comes out of protection with no issues, and overall the unit is working fine.
I cleaned every switch and pot at least once. I cleaned the relay.
BUT, here is the problem: I am getting what I describe as wind noise/static out of both channels when Phono 1 or Phono 2 are selected. This is more than just hiss, and not hum. It comes and goes, but is there more than not. Only on phono, dead quiet on AUX.
I know the usual culprits for this kind of noise are the notorious 2SC1312 and 2SA725. Especially on the EQ board. I have rebuilt the following boards, one at a time: Power Amp, Control Amp, Power Supply, EQ assy, Matrix Assy, and Decoder circuit. "Rebuild" in this case means replacing all small transistors: 2SC1312 (or 2SC1000, 1344) with KSC1345, and all 2SA763 with KSA992 (this unit had 763s, not 725s) but I replaced them any way. All electrolytic caps on all boards were replaced with either Nichicon UPW, UKL, UFG, Panasonic FC (power supply), or WIMA MKS2 for the small values.
I have checked solder joints, wiring (jiggled all at the selector switches), and ground points, but the phono noise is still there.
Noise is there with nothing connected to the phono jacks, with shorting plugs in the phono jacks, or a turntable connected, does not matter.
To try to narrow down the source, I connected the output of the EQ board (pins 14 and 17) to the aux input of my bench amp, and to my scope, and the noise it not there. So this tells me the noise is coming from downstream of the EQ. Once I determined it was not the EQ I went ahead and rebuilt the Matrix, board and Decoder board. No improvement.
The noise is present regardless of setting of the MODE switch (2CH, RM, SQ).
The only boards that have not been touched (yet) are the Protection board, the Sub-Channel (SQ) circuit, and the tuner board.
Anybody got any suggestions?
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