Help with piccolo j-310 pincushion

[Pjaska]

Hello, i bought this nice little 6 inch portable color television from japan (it was unconfirmed operation). Tv came wrapped in news paper and tape but it was in one piece i then went on and tryed it out and it worked normally except it had little bit of pincushion problems..

Tv model is piccolo j-310 and its made in taiwan, board says emperor PWB CTV 004D. I cant find schematics or any data on it.

I changed all electrolytic caps as google suggests + all film caps near flyback transformer but it didnt help.

Board has only pots for vertical position and size and b+ adjustment and AGC adjustment + some color pots at neckboard and un named adjustable coils i believe. I tryed the redneck method of messing with the screw driver but didnt help.

I got some scope pictures of signals but im not smart and experienced enough to do accurate diagnosis.

While doing measuring one of the caps blew up. I replaced it with old one and picture got narrower. I learned that it was bi polar cap that is one side to horizontal deflection coil and other leg goes to inductor who then passes the signal to ground. I looked in to it with scope and indeed voltage is spikeing just over 25v witch is capacitor rating. The old bipolar cap is very big in size compared to new one (same values 3,3uf and 25v) old cap dosent get very hot. I tryed shorting inductor to ground and picture got almost good, just little too wide and and still very little pincushioning. This made me to believe that it must be horizontal deflection yoke coil partially shorted becouse it isnt producing enough magnetism to image but still passes too much voltage to ground side(this is my theory but im basically guessing here)

I made some bipolar caps of regular caps to try different values but 3,3 - 5uf range seems optimal for picture widht but these caps go hot.
Old 3,3uf cap gives different widht then the one that blew up or 5uf that i made of 2 10uf caps

I then started to looking at horizontal output transistor (HOT) vaweforms and I also took amperage measurement from horizontal deflection circuit to see if its shorted or something i try puting up some photos.

Is here any experienced tech who can lead me to right way?


Horizontal output transistor voltage:blue and yellow is current of same circuit






Blue: voltage coming out of HOT
Yellow: voltage that is driving HOT






Voltage coming out of horizontal yoke coil. Is this normal looking? Seems odd to me and i cant find any reference vaweforms for this side of yoke.






Symptom

[Alex KL-1]

Bipolar caps comes with categories/types; rarer ones are for high ripple content. These are special ones, sometimes also found in tweeters in intermediate quality coaxial speakers.
If space allows you can use a film cap; heat problem solved.
But about the function of this cap... this serves for the H. linearity at one side; this don't affects pincushion, at least directly.
You mentioned about this cap being connected directly to ground, so I suppose this model not having any pincushion correction (special inductors or dedicated circuit. Some TV's really don't have any; they rely only on the CRT quality/design. And this can varies...
I've seen some pincushioning present on some 5" color CRT, but I cannot assume all need being the same.

[Pjaska]

Thank you for your valuable info, i was thinking if i could replace it with film cap and i even asked local tv repair shop guy but he didnt know if it would work.

The horisontal yoke coil ground side is connected to bipolar capacitor and goes through it (connected in series) and it then travels through inductor to ground (also in series). Sorry for my poor explanation im still learning electronics and english

I tryed connecting it directly to ground (bypassing the inductor) and it streightened image a bit but image was little bit too wide this way. you said it was "special" kind of inductor, i was thinking if i could get some general choke coils to try out if i could get it better?? Do you know if they could work?

[Alex KL-1]

About the cap, you can use "generic" polyester cap with proper capacitance; basically any will handle the required current (exception is the very small ones for signal).
The generic bipolar cap can be upsetting the horizontal linearity due to ESR. If this is the case, the poly cap will restore correct operation.
The series inductor probably is a premagnetized inductor for correcting the linearity at opposite side that the cap corrects. So, is a special kind of inductor, also. By the way, a pincushion one will resemble a mini transformator, with at least 4 terminals.

Then, is interesting to play with proper cap first, to see the result, with the linearity inductor in place.

[Pjaska]

I will order the right cap and report back. There is 4 legged mini transformer that is connected to drive the horizontal output transistor, is it the one responsible of pincushion?

[Alex KL-1]

Originally Posted by Pjaska

I will order the right cap and report back. There is 4 legged mini transformer that is connected to drive the horizontal output transistor, is it the one responsible of pincushion?

No, this is the horizontal output driver transformer, to better couple the pulses (it have a choosen turns ratio for adequately driving the base of H.out. transistor).

[Pjaska]

Hello, i have not ordered the cap yet but i did try to "reverse engineer" the circuit and heres the result:



I also looked in to jungle ic datasheet but i cant understand what to check out and if there is anything that i can adjust to make the picture more barrel shape.

I think where it said on datasheet 110v +b there is not voltages that high on that pin. And other parts of suggested circuits do not match 100% with actual circuits (i have done some schematics of those too but they are not ready yet).
Also when i was fooling around with settings i think it once got really good picture shape when i turned down g2 alot and picture was kind of dim, but when i switched to other game the geometry got really wobly...

[zeno]

This cap had a pretty high failure rate in older sets. I think it was ready to go
& blew on power up. The replacements wont work, they are the wrong type.
We used the OEM replacements as NP caps were hard to find.
Keep in mind the hoz out spikes can be quite high & lots of current.
Example is on a 25" TV the hoz out B+ is @120 volts but the spikes are
@ 1 KV
So I think the right type of cap will fix it maybe the PIN problem also.

73 Zeno
LFOD !

[JohnCT]

Consumer level TVs of this size never had any sort of geometry circuitry on board. Any distortion would be a function of the yoke design.

I have a feeling your original capacitor is fine as is and the pincushion error you're seeing is normal (remember that flat displays have spoiled us with their perfect geometry, perfect purity, perfect convergence, etc.).

Since the cap is old anyway, replace it with a good plastic one. Old scrapped plasma sustain boards are a good source of quality plastic caps in those value ranges.

John

EDIT: I have some caps in that size from a plasma. The brown one is 250V and the larger blue one is 315V. If you'd like one, I can stuff it in an envelope for you.

[Pjaska]

I will try to ask on monday if anyone local has the right cap. i tryed looking at my scrap philips chassis but it had no right value caps. It sucks paying 7€ shipping for 0,3€ part
That is really nice of you john but i wonder how long it would take to reach finland?
I also think that the cap will probably not fix the pin cushion tho.
How can i attach images to post like you did?... Never mind I figured it out!

This forum is very helpful and friendly place

[JohnCT]

Originally Posted by Pjaska

That is really nice of you john but i wonder how long it would take to reach finland?
I also think that the cap will probably not fix the pin cushion tho.

I don't know how long it would take to get there, but I bought an oddball vacuum tube off ebay years ago from somewhere near you and it took about three weeks if I recall correctly.

I got my collection of high value/high voltage plastic capacitors from the sustain boards of plasma TVs I scrapped out - very handy in rebuilding bypass filters in old tube radios and such - once done they will last forever. If you can ask a local repair shop if they have any scrap sustain boards they're willing to give you, that's a good place to start.

In any case, if you'd like either or several of those caps I have I'd be happy to put them in a padded envelope and mail them to you.

I also don't have a lot of faith that a new cap will correct your pincussion error. Can you post a picture of it running?

John

[Pjaska]

Here it is running, i think it looks worse in person. S/N looks good to me but E/W is bowed inward.





It is bowed so much that i dont think it left factory this way..

I will ask monday if anyone has caps or scrap boards so i would not have to wait 3 weeks

[JohnCT]

Honestly, if I repaired that TV I wouldn't have given the bow a second glance. It looks within the expected geometry of a TV that has no active pincussion circuitry. Only a change in the deflection yoke design would change the geometry.

At the time that TV was made, all the images viewed on it would have been full screen and that hard border would have been overscanned out of view. Only a TV program that showed a (for instance) doorway on one side or the other would have been noticed (and how long would that door have been in the shot?) or if it was connected to a video game with fixed sides.

I do remember getting some complaints on geometry when Pong first started selling. On typical live video that most people would be using the TV for, most people simply didn't notice.

For capacitors approaching .5uf (500nf) that are not electrolytics, plasma sustain boards are a gold mine. I have several poly types that are over 5uf at 200V or so. Sustain boards need higher value capacitors that have the low ESR of plastic caps, so they don't use electrolytics for coupling.

If you run into a dead end, let me know.

John

[Pjaska]

You might be right.. As it is now there is not enough overscan to hide the bowing(black bar is visible next to "sandstorm") but when it had the new cap that blew up image was little bit wider (more over scan) maybe the cap has dropped out of spec and it was like that.

If this the case then my next queston will be is there a way to hack this circuit (tweak component values or add/remove components) or would it be possible to add magnets to the sides or some other way to get it even a little better? It really looks annoying when playing games becouse they have lots of straight lines everywhere and i keep staring the geometry and not focusing on the game

[JohnCT]

It's possible a little more width might cause a slight change/improvement in the pin distortion...

Replace the BP cap and reaccess.

The problem with adding magnets is that it will affect the purity and convergence, and make the TV more sensitive (purity wise) to compass rotation. If you want to try, use the soft "refrigerator" advertising magnets like you get from a car dealer (for instance). Cut it into small squares and try moving around the yoke to see if it helps your pin distortion, but be aware of purity and convergence changes at the same time

John