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Sony XR-C5300, car radio -failed tuner block

Owner likes the 2 SW bands, other than find a broken one or related model also with the same tuner TUX-020 , any ideas? Courtesy of some Danish and Polish threads someone found out that the 80 pin Philips tuner IC TEA6842H is likely the same as the one badged Sony

8-759-653-23 in this tuner. All DC at the tuner 19 pins agree with Sony Schema and rails, Xtal lines etc agree with the TEA... datasheet. There is local Xtal osc, serial data and clock line signals on engaging "SEEK" , front display shows changing f but the TEA pin 42 tuning V stays at 0.045V. Nothing amiss DVMing around the variable cap diode , pushing IC pins if loose, and no bad ESR local caps. Whatever occured happened in a garage during a cold spell of weather, vehicle rarely used.
Reply to
N_Cook
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Try bringing in an external tuning voltage. If by varying this voltage you can get an IF output from the front end (and receive a channel at that point...) then you know the front end transistors etc are OK and you either have a bad PLL chip or no oscillator sample going to the PLL chip.

Mark Z.

Reply to
Mark Zacharias

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I was going to try a 20 turn preset Saturday but got waylaid - a job for today. Everything checked ,so far, pinning-wise has agreed with the TEA datasheet and they are available but a/ no confirmation that the Sony and TEA are the same b/ desoldering 80 pin .5mm spacing IC is fine , it is the soldering in of the new one I would be wary of, despite my express removal technique leaves an alignment "ghost" in the original solder pattern.

Reply to
N_Cook
20 turn 25K preset and 4K7 to the cathode of the varicap something like BB156 marked F4 so probably HVC383B . AM and FM stations come in , so VCO etc ok. Display showing bottom of the band of course. Another possibility is corrupted serial link data between master controller and this TEA tuner IC
Reply to
N_Cook

Just one more thing to check. Once you tune in a station, remove the tuning voltage source. If the station stays tuned for a few seconds, then you'll know the problem isn't caused by leaky varicaps. If the frequency immediately drifts, the varicaps need to be replaced. Chuck

Reply to
Chuck

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80

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you

either

Interesting point to check, willdo

Reply to
N_Cook

model

80

is

you

either

Incidently the radio data system works back to the display so even less likely corrupted serial link going the other way. Cutting my applied tuning voltage , the station goes off tune immediately. I've not managed to get my head around the control system - a chicken and egg situation ? Could a leaky varicap lead ,around the houses , to failure to have an applied tuning voltage through the chain of VCO / PPL etc ?

Reply to
N_Cook

I'm not exactly sure what you are asking, but if there was leakage that caused the tuned frequency to drift immediately, we mainly replaced the whole tuner. (The VT line must be disconnected at the VT terminal on the tuner before doing this test.) Exceptions were Pioneer tuners or RCA televisions where the tuner was a section of the main board. Of course, any part which can go leaky on the VT line can cause this symptom. Chuck

Reply to
Chuck

I vote for the PLL chip. If the varicap were leaky, you'd see some voltage there as you tried to tune; I've seen this just limit the tuned frequency to say 95.1. If the cap were very leaky, even applying an external voltage wouldn't get you a station. The varicap bleeds off quickly mainly because it's capacitance is very low to start with. Most PLL chips have a couple buffer transistors between the tuning output of the chip and the actual front end. You can look there, but my guess is you'll see nothing.

Mark Z.

Reply to
Mark Zacharias

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