1. Home
  2. Electronics Repair
  3. No horizontal output from IC, please help

No horizontal output from IC, please help

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: peter snipped-for-privacy@engineer.com 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
Reply to
John Smith
Loading thread data ...

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

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Reply to
sofie

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

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.
Reply to
Franc Zabkar

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 peter snipped-for-privacy@engineer.com

voltage

Reply to
John Smith

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

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.

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.

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.

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

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

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.
Reply to
Franc Zabkar

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

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.
Reply to
Franc Zabkar

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.