Horizontal frequency

OK, we'll be all too glad to give you as little help as possible.

The answer to your question is maybe.

OK Art, here it goes - Sanyo model #HT32744, chassis #32744-00. Hit power button, Relays click, high voltage starts, then relay clicks again and set shuts down (approx 2 seconds time). Can repeat this once before having to unplug the set to repeat this sequence. I have checked the power supply including the SMPS which is operating normally. I have 140vdc at the collector of the HOT (steady). There is a power failure circuit that I am trying to understand by looking at the schematic. I disabled this (set stays on) to keep the set running long enough to check a few more voltages. Even though the set stays on, there is a faint raster in the middle of the screen about 2" square that pulses (seems to be in sync with the slight ticking noise of the flyback). The screen and heater voltage is swinging all over. I have never checked these voltages on a working set, so I'm not sure what's normal. I work on TV's as a hobby, and have about 2 years experience. I have a good basic understanding of electronics and electricity, and am self taught with the exception of help from this group. This is why I may ask some seemingly retarded questions. I hope this is enough info. Thanks for replying.

As others have said, information is key. However there are a couple of things you might try to zero in on the problem:

From your comments, I assume that the HOT is not shorted. Jumper the base to the emitter of it to force it to stay turned off and see if the power will stay up. Of course you will not see a raster due to the HOT being shorted out, but if the power stays on your problem is located on one of the output terminals of the flyback transformer. If this is the case look for a shorted diode off of one of those secondary windings.

It could be other things, but that is often the reason based upon the symptoms you described.

Thanks for the reply Ken. For the sake of me explaining everything I've done in the past 2 hours, I think I found a problem on a 6.5V supply. It goes to the P in P module, an RGB drive IC, and somewhere in the video deflection circuit I think. Long story short - removing power from this 6.5 regulator keeps all voltages stable off the SMPS. I was going to disconnect the output of this regulator first though to see if it was OK.

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Art, I thought my questions (yes/no/possibly) were pretty straight forward, but obviously I was wrong. "if the frequency isn't what it should be (suppose to be around 15.7Khz?), would this likely be part of a protection circuit shut down in some models? Would the same be true for Vertical as well? " Peter gave a better answer (maybe) anyway. Thanks

On Mon, 04 Jun 2007 15:25:02 -0700, Golf put finger to keyboard and composed:

I have seen a fault of this kind in an old IBM monitor. A ceramic cap drifted in value, causing the horizontal frequency to increase (or was it the duty cycle?), which in turn caused the pulse amplitude on the collector of the HOT to increase. This was reflected in a secondary winding of the FBT which then triggered the HV protection and shut down the unit.

- Franc Zabkar

I gave this guy several pointers in multiple posts about HV protect over the last several days. He seems pretty able for a hobbyist but it's tough when you don't have shelves stocked with new and good pulls to sub.