Sony XR-C5300, car radio -failed tuner block
N_Cook
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.
Mark Zacharias
news:iijkvl$g3t$1...@news.eternal-september.org...
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.
N_Cook
news:4d4f48ea$0$29669$c3e8da3$92d0...@news.astraweb.com...
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.
N_Cook
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
Chuck
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
N_Cook
news:lu10l616sepoipln3...@4ax.com...
Interesting point to check, willdo
N_Cook
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 ?
Chuck
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
Mark Zacharias
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.