Teac TV ctm687 tuner problem.

I am repairing this Teac TV ctm687 which has a grainy picture on all
channels; even when using the vcr (however the tapes play a normal
picture.
Hence I suspect the tuner (oscar 2900kkc) for which I measure 7.87
volts at the AGC pin which goes to i/c TDA8305A pin 5 which according
to TV schematics should only have 3.9 volts.
My B+ at the tuner is 12.11 and I wonder if this is the correct supply
voltage to the tuner.
Thanks in advance.
Al
Reply to
alitonto
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This can be a defective RF stage in the tuner, or an AGC fault. The tuner, when defective is changed as a module. You would be best off to order the service manual and follow it through, or give out the set for proper service. Take care for serious safety issues when working in TV sets.
Jerry G.
Reply to
Jerry G.
This particular model tuner by the way, was made by Temic.
--
Met vriendelijke groet,

   Maarten Bakker.
Reply to
maarten
Thanks for comments. What I need to be sure is that infact the tuner is at fault. I have tv schematic but it doesn't show enough details about what voltages should be on each pin of the tuner. Can anyone help with another check I could do to be sure the output voltages of the tuner are infact at fault? Is it possible for the higher voltage at the AGC pin to be caused by somethingelse?
snipped-for-privacy@panic.xx.tudelft.nl wrote:
Reply to
alitonto
On 17 Jul 2005 05:17:30 -0700, "alitonto" put finger to keyboard and composed:
Am I right in assuming that you are playing back tapes through the AV inputs of your TV?
That could just mean that the AGC circuitry is cranking up the gain to compensate for a weak or absent signal.
This sounds typical.
I don't have any experience with your particular set, but here are some general tips.
Check that the band switching pins (BU, BH, BL) respond to band changes (UHF, VHF high, VHF low). Also check that the tuning voltage (VT) increases and decreases smoothly as the channels are scanned.
See the bottom RH corner of this page for a typical pinout:
formatting link

- Franc Zabkar
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Please remove one 's' from my address when replying by email.
Reply to
Franc Zabkar
from the sounds of it, the tuner is not at fault. THis is becasue you said the picture is still grainy when you use the vcr, which I'm assuming means when you have the vcr connected to the AV inputs and using , thus, the VCRs tuner to watch tv. I'd check your antenna wiring and connectors.
Assuming
-thats not what you meant
and -the tv tuner is faulty
and -the vcrs tuner is fine
and -your time is worth anything at all to you
just use the vcr's tuner to watch tv, and stop risking breaking the set and just wasting time.
Reply to
Arpit
"Arpit"
** You are correct.
The OP simply has a bad antenna.
The OP is an absolute dickhead.
......... Phil
Reply to
Phil Allison
Not necessarily - some VCR feed to the TV per RF to a no station-on-there-channel, and not via an AV input - if this is the case then could still be a tuner prob
David
Phil Allis> "Arpit"
Reply to
quietguy
"quietguy"
**Quote:
" I am repairing this Teac TV ctm687 which has a grainy picture on all channels; even when using the vcr (however the tapes play a normal picture. "
How come it plays OK with tape as the source???
..... Phil
Reply to
Phil Allison
Good point
David
Phil Allis> "quietguy"
Reply to
quietguy

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