Attempting to repair a JVC 4VR 5456X CD-4 Demodulator Problems.

[Paul Pettegrove]

Hello all ..this is a great thread ..Ive just recently bought a 5456 in the Uk and have been putting it through its paces …I realise its going to need a service as its very noisy with all speaker outputs creating hiss. It seems to be doing what its meant to though. I have a question on that stereo separation knob on the front as its not referred to in the HIfi engine download manual. Can anyone explain it ?
Are there any dos and donts in servicing this amp. Im sending it to a repair person today.Welcome to the vintage rabbit hole of Quadraphonic.

 

[par4ken]

Hello all ..this is a great thread ..Ive just recently bought a 5456 in the Uk and have been putting it through its paces …I realise its going to need a service as its very noisy with all speaker outputs creating hiss. It seems to be doing what its meant to though. I have a question on that stereo separation knob on the front as its not referred to in the HIfi engine download manual. Can anyone explain it ?
Are there any dos and donts in servicing this amp. Im sending it to a repair person today.

With CD-4 it is necessary to adjust for best separation.

CD-4 uses a combination of FM and PM (PM is related to FM). With FM the demodulated signal comes out the same level regardless of the carrier level. That distinguishes it from AM and is why it is more immune to noise. The demodulated difference signal is mixed with the audio signal from the phono cartridge fed via the RIAA preamplifier. Phono cartridges vary in output level over a wide range, necessitating the adjustment for best separation.

 

[jupp369]

Thanks a lot for that 5456 manual!
Does anyone has a detailed circuit from a CD-4 board of this factory line? I mean not only the circuit, but with ALL voltages (special right side) for a new calibration.
My (new) 5446X put suddenly always the radar on, no chance to switch it off and the supply main resistor get's hot. I got cold sweats! After a couple of days everything gets normal.
But still the old problem: low amplitude compared to all other modes. 5446X has no more any potentiometer in CD-4 like the other before.
(It's rewired with new matrix boards)