Sony XR C5300R car radio

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.

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

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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

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.

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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

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

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. ?

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

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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.

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