Sony XR C5300R car radio

[N_Cook]

First of these looked as though a failure of the tuner block. Owner bought
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 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. So not a false muting problem

Some of the main chip SM solderings seemed suspect so redid the non LCD
segment ones. 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.
I'm assuming some data problem but what changes between sending data to and
from the tuner to load the presets and normal listening mode?
Schematics are out there for this model

 

[N_Cook]

I don't remember seeing this since the days of wired-in VCR remotes. A chain
of R varying from 680R to 10K for 11 of the main key switch sensing, not
diode array. That single resistance-set control line goes through the 14 pin
lift-off front panel connection to the main micro. Was thinking if outside
the allowed range, or dirty contacts, then perhaps an illegal mode, but they
check out true considering E12 series. High probability of a break somewhere
in such a chain of SM resistors.

 

[N_Cook]

I have seen this scheme of button sensing on many audio units, particularly
of Sony manufacture. Makes for very simple software to determine which
button has been pressed. The CPU only needs to read a single A-D input pin,
and then compare the result to a lookup table programmed with what function
belongs to what sensed voltage.

Arfa

Made a return with effects selection, with a standatd pot, on likes of
Roland Cubes.

One other person out there had this symptom ( unanswered)
"Im trying to fix an old car stereo, Sony XR-410. Cassette player works fine
but there is no sound in FM mode altough the frequency is displayed."
but as not a commonly reported fault I have to continue with front panel
fault cue

 

[Mark Zacharias]

First of these looked as though a failure of the tuner block. Owner bought
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 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. So not a false muting
problem

Some of the main chip SM solderings seemed suspect so redid the non LCD
segment ones. 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.
I'm assuming some data problem but what changes between sending data to
and
from the tuner to load the presets and normal listening mode?
Schematics are out there for this model

Not totally out of the realm of possibility that the two could both have bad
front ends. Have you tried applying an external tuning voltage?

Mark Z.

 

[N_Cook]

Not totally out of the realm of possibility that the two could both have bad
front ends. Have you tried applying an external tuning voltage?

Mark Z.

I did with the original one and you can manually tune via a 10 turn pot to
change stations with audio emerging from the pa. No reason to assume any
different with this one but as awkward to get to I will leave as is



Another possible variable is battery B+ but there is good regulation . With
no key presses the micro-sourced voltage is between 4.81V and 4.83V with no
power output , and invariant with "battery" between 12V and 14V

Measuring the keyed voltages , K-0, for the front buttons, pulls down to
left buttons 1.14,.60,.03V
central 1.50,.81,.33,2.57,3.69 V
right 1.83, 3.37, 3.00 V
I wonder what the acceptance bands for each of the 11 functions is in the
look-up table. I will guess at 1/3 of an interval with 1/3 for gaps for
unplaced or perhaps error so about .1V out and problems can ensue.
Will have to see if those voltages agree with the resistance chain, not
simple correspondence nor necessarily linear intervals. Minimum gap is .81 -
..6 V which looks suspicious at this stage. K-1 is similar resistance change
system for the other more minor function 8 buttons, I suppose I had better
check those also

 

[N_Cook]

unfortunately, including the .6 and .81V, all step V agree with scaling the
voltages of the resistance ladder on schema and reality, assuming a 10K
dropper inside the microcontroller.
Varying only about 20mV on any step

 

[N_Cook]

I don't know how this unit should function but this does not seem right.
Leave a tape in the unit and switch on with the front flap in place. Unit
recognises there is a tape inplace from initial jiggle. Then drives the tape
into the closed front flap , so slip clutch or whatever engages. "Nose
switch" , door switch , reset and tape present sw all function but what is
the point of sensing a tape present and sensing the door is closed and
trying to eject a tape into it. ?

 

[N_Cook]

You haven't refitted the front panel part that has the flap in, and failed
to hook the lift pin over its lever or something, have you ? This is a
common problem with VCRs, and if you don't get it positioned right, you get
the exact symptom you are describing. With VCR's, it is necessary to stick
your fingers in the flap, as you clip the front back on. That ensures that
the pin is correctly located over the lever, to allow it to lift the flap as
it cranks the tape out.

Arfa

I'd removed the tape deck and refitted but as confined space the controls
connector was refitted skew, it does now leave the tape in place at switch
on. I disabled the unused R/C receiver as that seemed stuck at 4.5v output
regardless of what random IR I fed to it, RS 170 chinese data out there.
Will reconnect and scope it properly today but am how at the Sherlock Holmes
stage

If you have eliminated all the possible then all that remains , however
unlikely, is the highly improbable - Same tuner fault with 2 randomly
obtained units.

 

[N_Cook]

I've just remembered I never checked the other A/D resistor chain for the
number buttons .

With the other chain , 4.83V V ref , you only have to add a pot and 100K or
so on the line to ground and bring that voltage down to 4.7V and that
disables any key sensing, whether it drops it to 3V or 0V on a key push. So
grime in the general sense could cause that symptom