Sony XR C5300R car radio
First of these looked as though a failure of the tuner block. Obtained
another one for spares, removable front display missing.
This one has exactly the same fault symptom so more likely a problem with
the front panel (or improbable same tuner fault on 2 separately acquired
units).
Tuner will go into auto strongest signal search, BTM, and store in memory and also
readout follows manual input of frequency and stores in memory but at no
point does the audio come through to the output amp.
Pressing the presets shows the frequencies but no audio. Injecting local
modulated RF in there and audio is outputed and stays invariant on pressing
any preset so stuck on one RF tuning setting, probably bottom. So not a false muting problem
Cleaned the 14 pin front to interior header plug. No stuck
closed keys. It looks as though the front has been kneed at some point as
the ring around the rotary encoder button is cracked but no pcb problems
found.
The LCD clock, CE and data lines between the 14 pin header and the 64 pin
chip trace through. Not possible to scope anything on the board without
making up a one-off extender cable. The main chip internal flash write line
that comes out to the fronmt is clear of anything that may take it low.
The voltages on all the keys agree with the resistance chains of the 2 A to D
converter lines in the schenmatic.
Pressing reset makes no difference. Front panel does not load down the
B+ voltage of the main board any more than pressing the nose switch
with the display front removed.
I've not repeated it for the second one as I assume it is the same as the first on , If I
introduce a variable voltage to the tuner tuning control then the tuner works and
it outputs audio.
Anyone happen to know what, on the removable front panel. can go wrong and
inhibit the radio ?
