Hello all,
I have been trying to fix my TV which has sound, but no picture.
I am not very good at fixing TVs, and was wondering if someone could help
me.
The power supply voltages are ok, and there is no life in the high voltage
transformer.
The circuit that supplies the transofrmer has DC but no AC.
As I understand it, it is fed by the horizontal out of the AN5607 chip.
I measured all the pins on this IC, but I don't know what to expect.
I have listed my findings below.
Can anyone help please?
Please reply to my email address:
Thankyou in anticipation.
Peter



Test 30/08/05 AN5607NK

Pin
1 GND
2 sig
3 sig
4 sig
5 sig
6 low level sig
7 sig
8 sig
9 sig
10 sig
11 sig
12 sig
13 low level sig
14 sig
15 gnd
16 low level sig
17 low level sig
18 sig (not connected)
19 NO SIG
20 no sig
21 no sig
22 sig
23 sig
24 sig
25 9V DC OK
26 no sig
27 sig
28 sig
29 sig
30 not connected
31 9V DC OK
32 no sig
33 low level sig
34 sig ? Could not measure properly, but there was something there
35 no sig
36 no sig
37 no sig
38 no sig
39 no sig
40 no sig
41 no sig
42 sig
43 8V DC OK
44 no sig
45 no sig
46 6.3V DC OK
47 no sig
48 no sig
49 no sig
50 no sig
51 GND
52 sig

Peter/John Smith:
Exactly what are you "seeing" for horizontal pulses coming out of the chip?
What does the waveform look like... please describe the amplitude,
risetime, and length of the pulses that are being fed to the HDr xstr.
It looks to me from your post and listing of your measurements that you
might not be using a scope.... you need one for what you are trying to
measure..... or take a chance and replace the chip as long as you have
checked all the surrounding circuitry including the HDr, HOT,and LOPT.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -




"John Smith" wrote in message
...


Hello all,
I have been trying to fix my TV which has sound, but no picture.
I am not very good at fixing TVs, and was wondering if someone could help
me.
The power supply voltages are ok, and there is no life in the high voltage
transformer.
The circuit that supplies the transofrmer has DC but no AC.
As I understand it, it is fed by the horizontal out of the AN5607 chip.
I measured all the pins on this IC, but I don't know what to expect.
I have listed my findings below.
Can anyone help please?
Please reply to my email address:
Thankyou in anticipation.
Peter



Test 30/08/05 AN5607NK

Pin
1 GND
2 sig
3 sig
4 sig
5 sig
6 low level sig
7 sig
8 sig
9 sig
10 sig
11 sig
12 sig
13 low level sig
14 sig
15 gnd
16 low level sig
17 low level sig
18 sig (not connected)
19 NO SIG
20 no sig
21 no sig
22 sig
23 sig
24 sig
25 9V DC OK
26 no sig
27 sig
28 sig
29 sig
30 not connected
31 9V DC OK
32 no sig
33 low level sig
34 sig ? Could not measure properly, but there was something there
35 no sig
36 no sig
37 no sig
38 no sig
39 no sig
40 no sig
41 no sig
42 sig
43 8V DC OK
44 no sig
45 no sig
46 6.3V DC OK
47 no sig
48 no sig
49 no sig
50 no sig
51 GND
52 sig

On Tue, 30 Aug 2005 07:08:58 +1000, "John Smith"
put finger to keyboard and composed:

I have been trying to fix my TV which has sound, but no picture.
I am not very good at fixing TVs, and was wondering if someone could help
me.
The power supply voltages are ok, and there is no life in the high voltage
transformer.
The circuit that supplies the transofrmer has DC but no AC.
As I understand it, it is fed by the horizontal out of the AN5607 chip.

If there is a fault in the line stage, or if the B+ is excessive, many
sets are designed to go into protection mode. Often you will hear a
quick hiss of EHT followed by immediate shutdown.


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

All,
Thankyou for your replies.
BTW my name is Peter and not John Smith (silly outlook setting at the time)
I'll reply here to all the posts I got so far.

Donald - I don't think the problem is a dry joint on the flyback trasformer,
The joints look OK, and there is no life from the flyback if I prod it.

Daniel - Yes I am using as CRO, I borrowed a 100mghz HP from a friend,
but did not spend much time in trying to figure out how to use it.
If I knew where to start looking, I would probably spend more time
connecting the test lead properly, and analysing.
As to your question, the horizontal output from the chip (pin 19, I attached
a block diagram of the IC in my original post,
but it did not come through) Anyway, the Horizontal output is non existant.
Ie = zero.

Franc - I think that your onto something here.
On powerup, I do get a brief static pop as if the tube is firing up, but
nothing else.
Is there some indication to show that the set has gone to protection mode?
I don't know what the "line stage" of the "B+" are, but I did find that pin
20 on the chip is called the
"High voltage detection/shut down input", so I could trace back through the
schematic to see where it goes (I guess).
But how can I test for excessive voltage?
Correct me if I am wrong, but if the chip goes into protection mode, then
the excessive voltage is likely to be shut down as well?
I could, disconnect pin 20, but don't I then run the risk of frying more of
the set?
I remember reading an article where someone used an auto transformer to
bring the mains up slowly,
but I don't have one, and it's not likely to work on a switch mode power
supply anyway.

Anyway,
I'll go away and prod the TV some more now.

Thanks once again for your tips & pointers (tups & punters if your a Kiwi
:-).
Peter



"Franc Zabkar" wrote in message
...
On Tue, 30 Aug 2005 07:08:58 +1000, "John Smith"
put finger to keyboard and composed:

I have been trying to fix my TV which has sound, but no picture.
I am not very good at fixing TVs, and was wondering if someone could help
me.
The power supply voltages are ok, and there is no life in the high
voltage
transformer.
The circuit that supplies the transofrmer has DC but no AC.
As I understand it, it is fed by the horizontal out of the AN5607 chip.

If there is a fault in the line stage, or if the B+ is excessive, many
sets are designed to go into protection mode. Often you will hear a
quick hiss of EHT followed by immediate shutdown.


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

On Wed, 31 Aug 2005 09:14:00 +1000, "John Smith"
put finger to keyboard and composed:

On powerup, I do get a brief static pop as if the tube is firing up, but
nothing else.
Is there some indication to show that the set has gone to protection mode?
I don't know what the "line stage" of the "B+" are, ...

The "line" stage is just another name for the horizontal deflection
system. The B+ voltage is the main voltage (typically 100V - 150V)
that supplies the line stage. You'll find it feeding the primary
winding of the flyback transformer. Another way to locate it is to
look for the heaviest diode on the secondary side of the switchmode
transformer and an associated 160V (or higher) electrolytic cap.

... but I did find that pin
20 on the chip is called the
"High voltage detection/shut down input", so I could trace back through the
schematic to see where it goes (I guess).

There are at least two common methods of protection used in TVs. One
involves sensing the amplitude of the flyback pulse from a winding of
the flyback transformer. This looks to be what is happening in your
case. A second method senses the beam current via a resistor in the
bottom end of the flyback's HV secondary winding.

But how can I test for excessive voltage?

Locate and measure the test points alluded to above. If the B+ voltage
is much greater than the spec, I would suspect any small electrolytic
capacitors on the primary side of the switchmode transformer.

Correct me if I am wrong, but if the chip goes into protection mode, then
the excessive voltage is likely to be shut down as well?

The flyback pulse that triggered the protection will disappear, but
the B+ voltage will probably still be there.

I could, disconnect pin 20, but don't I then run the risk of frying more of
the set?

Most definitely, not to mention potentially excessive X-ray emissions.

I remember reading an article where someone used an auto transformer to
bring the mains up slowly,
but I don't have one, and it's not likely to work on a switch mode power
supply anyway.

If you need to test the B+ supply on its own, you can disable the line
stage by shorting the B-E junction of the line output transistor.
Otherwise you can desolder its collector or its base. Then wire in a
suitable dummy load across the B+ supply. I use a 240VAC 100W
incandescent globe.


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

On Wed, 31 Aug 2005 20:16:18 +1000, Franc Zabkar
put finger to keyboard and composed:

But how can I test for excessive voltage?

Locate and measure the test points alluded to above. If the B+ voltage
is much greater than the spec, I would suspect any small electrolytic
capacitors on the primary side of the switchmode transformer.

I should have said that another common fault which gives rise to an
excessive flyback pulse amplitude is an open or partially open tuning
capacitor. This is often a metallised film type (eg 10nF 1.6kV)
connected between the C and E of the HOT (horiz output transistor).


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