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

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.

In sci.electronics.repair Jerry G. wrote:
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.

This particular model tuner by the way, was made by Temic.

---
Met vriendelijke groet,

Maarten Bakker.

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?

wrote:
In sci.electronics.repair Jerry G. wrote:
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.

This particular model tuner by the way, was made by Temic.

---
Met vriendelijke groet,

Maarten Bakker.

On 17 Jul 2005 05:17:30 -0700, "alitonto" put
finger to keyboard and composed:

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.

Am I right in assuming that you are playing back tapes through the AV
inputs of your TV?

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.

That could just mean that the AGC circuitry is cranking up the gain to
compensate for a weak or absent signal.

My B+ at the tuner is 12.11 and I wonder if this is the correct supply
voltage to the tuner.

This sounds typical.

Thanks in advance.
Al

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:
http://www.wagner.net.au/Catalogue/03_01.pdf


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

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.

On 17 Jul 2005 05:17:30 -0700, "alitonto"
wrote:

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

"Arpit"

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.



** You are correct.

The OP simply has a bad antenna.

The OP is an absolute dickhead.




.......... Phil

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 Allison wrote:

"Arpit"

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.


** You are correct.

The OP simply has a bad antenna.

The OP is an absolute dickhead.

......... Phil

"quietguy"
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

**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



Phil Allison wrote:

"Arpit"

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.


** You are correct.

The OP simply has a bad antenna.

The OP is an absolute dickhead.

......... Phil

Good point

David

Phil Allison wrote:

"quietguy"
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

**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


Phil Allison wrote:

"Arpit"

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.


** You are correct.

The OP simply has a bad antenna.

The OP is an absolute dickhead.

......... Phil