Predicta Princess
 

I am new to the TV repair thing and have a couple issues with my Princess model TV. On the bench in pieces it seemed to work fine after a full recap and reresistor but once reassembled into the cabinet I am get HV arcing at the HV connection to the picture tube, what would cause this?
Another issue is the horizontal is not very stable, it will go out of sync if I change channels or start and stop the vcr, any thoughts on this?
Thanks

Gregb

Have you thouroghly cleaned the area around the HV connection to the CRT? Does it only loose synch for an instant or does it stay out of synch? Temporary disturbances in synch are to be expected on video source switches.

I have not cleaned it but I will give that a try. When it looses synch its gone and I have to re-adjust the horz control to bring it back or it will never come back.

Gregb

IIRC there is one or more of those 'K' networks in the horizontal, did you replace that? If not it is likely the source of your horizontal problems...

Sometimes if there is good synch range on a hold control it has to be set to a certain spot within (sometimes the edge of) the range to keep hold on scene transitions.

AGC adjustment can sometimes be critical to synch stability too.

In addition to all above,
Dress the yellow CRT lead away from all yoke and high voltage wiring
Make sure the CRT is properly grounded
Align the horiz osc per instructions. It is easy and important.
There is no AGC adjustment

Thanks for all of the suggestions and no I did not rebuild the "K" networks but I think I will go back in and do them all. The bigger problem at the moment is the arcing at the HV connection to the picture tube. I pulled the cover and cleaned it with no improvement at all. I am afraid it will damage the flyback if I don't solve this issue.
Thanks for any suggestions.

Gregb

Do you have arcing where the HV wire connects at the base of the 1B3 HV rectifier tube inside the HV box or at the other end where it connects to the picture tube ?

Is there anyway you can measure the high voltage? Maybe it's running too high. Worst case scenario, if your voltage is correct but it's still arcing, you can always use RTV33 high voltage silicone to cover the entire area. This stuff is also great for re coating flybacks. Not cheap though. Bob Andersen has a lot of info on this as well as rebuilding networks, using either a cluster of parts covered in epoxy, or little pieces of vero board used. Both are effective and do the job nicely.

The other consideration you may want to try is replacing the high voltage lead with a modern one. I've gone on night walks armed with a screwdriver and wirecutters many times to salvage this cable out of curbside TVs, and I use it to replace all sections of the high volt cable in my Predictas.

The arcing may be disrupting the sync. The RC networks are pretty reliable, especially the dark red Erie Pacs.

I suggest fixing the arcing before getting into the RC networks.

It is arcing right at the connection to the picture tube. You can see and hear it shooting out about 1/2" in all directions around the connection. Its strange that it was fine when on the bench and only started doing this once back in the cabinet. I will put the HV probe on it when I get home and see what the voltage is. When on the bench I did take a reading and it was just under 15k.

Gregb

that is odd that it would arc like that with just 15kv unless the cable at the anode of the crt got knocked loose and is not actually in contact with it.

agree with the grounding, of the dag, I would ohm that to ground and make sure the spring or what ever was used is still in place and the ground is good.

If the dag is not grounded it could become charged and start arcing from the dag to the nearest ground.

I did have the cover off last night and cleaned the tube real good and made sure the connection was properly made and it was and still is. The arcs are radiating out from the nipple on the tube in 3-4 different directions and about a 1/2" long making that nice sizzling sound.
I did clean the whole tube and made sure the ground spring was in contact with the tube but did not ohm it out, I can check that as well.

Gregb

Did you clean the conductive coating off the tube??? If so, the spring is not grounding the tube, it's touching just glass.

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I don't think so, I used some Windex on a paper towel and nothing more than some dust came off.

Gregb

If the CRT HV connector is a suction cup there is a possibility that the lead has broken off the the metal clip inside the rubber where it is not visible, and that could be causing/worsening the arcing you are seeing.

This one is just a metal clip on the end of the wire. I went home over lunch and checked the voltage and it is still just under 15k. The arcing looks like it is comes from the hole the clip snaps into and they run out in random directions like I said about 1/2".

Gregb

very strange indeed. Correct no cup used on predictas, just the clip. should be fully seated inside the hole of the anode.

the dag should be grounded, try reading the dag to the ground (just touch one lead to the grey dag and one to chassis ground), it will prob be several hundred ohms since its (dag) not a perfect conductor. Wiping off can be problematic, I have seen dag wiped right of, sometimes its dust but you should still see a grey/back coating clearly on the back of the CRT (except around the anode).

I generally don't overly clean things EXCEPT around the anode and around the HV cage.

Got the arcing problem solved, pulled it all apart again tonight and had a good close look with a nice bright light. There was a layer of scum on the tube around the connection point that the Windex wouldn't even touch, used some alcohol and a scotch brite pad and it cleaned up nice and it works great now with no arcing at all. The picture is really nice and the horizontal seems much better as well. Other than some adjustments I think its good to go.

Gregb

Hi GregB .
i was suspecting the cleaner you used left a residue. i see you found the issue.
i thought i should mention for the benefit of other vidkarma memebers that-

from what i have seen over the years, best way to clean high voltage areas is with alcohol.
i always checked that the alcohol i used left no residue by applying it to my finger and checking for any "oily" substance that was left after it evaporated.
methyl hydrate always worked good for me. common rubbing alcohol left oil.sometimes there is water in methyl hydrate so i always gave it 1/2 hour drying time before i fired up the high voltage,the high volage area has to be very clean!
cheers,
RonL

It wasn't a residue left from the Windex, not sure what it was as I could scratch it with a finger nail. I have found that regular drug store rubbing alcohol is not pure alcohol and maybe has an oil in it. You have to look for the 99% alcohol and it will leave no residue and evaporates within almost seconds.
Thanks for everyones suggestions.

Gregb