high voltage loss

[timmy]

hey all yet another problem i cant seem to get to the bottom of. has anyone ever come across a low hv problem and tried to trouble shoot it by removing the 6bk4 cap, or the crt plug, or the focus tube, and come up with the same hv,10kv bright up, turn down to get clear pic and the hv is 15kv.all tubes are good and tested, replaced all electrolytics.checked cathode current and its alittle confusing because this set has 2 hot in paralle and had to break the 2 cathodes to check but the sams shows for each one is to be 105ma but this is coming up at 220ma either together or separate both 220ma and cannot get it to adjust, it will go up alittle but wont go below 220ma and also sams states to put a meter across r155 and adjust eff coil to get 1.2 volts dc but i get nothing across that resistor. of course sams states turn bright down to min, and set hv to 24kv befor doing any of this but i cant get the hv and at a loss for what is going on now, i thought the fly may be going but just dont know. this is the set from grimer, the 66 motorola 23 inch color, its odd.

[Zenith26kc20]

Doubt it is the flyback as Motorola flybacks were about the most reliable we ever dealt with. I remember only one bad and the customer was the one who killed it. Can you give a chassis/model #?

[timmy]

the chassis is ets 908ye. what struck me as very strange is that sams calls for 105ma for the cathode current on each hot and when i had put the meter on and check i got 220ma on each and could not get it down to 105 so now days later i check it again and one tube now shows 115ma and the other 110 and wont go lower and i did nothing to the set to have made anything change. the model is 23rl325bw but this one has the sliding doors in front but it would be the same sams set 856 folder 1. i also checked the b+ voltage which supposed to be 385vdc but is running at 410-412 vdc which i think maybe alittle hi suggesting a possible short somewhere or maybe this is normal for this set, i just dont know at this point. i also tried 3at2 rec, 6bk4,and even took the anode lead off the crt and checked the hv that way.

[ctc17]

you have two sets that have 12kv that's not very possible because at 12kv there won't be enough pulse to heat the hv rectifier filiment so you would have nothing maybe it time to get your measuring instrument calibrated

[timmy]

well at least when i did certain tests with the other set i did get 30kv on my hv tester and with the first set it seems now that the crt maybe loading down the hv on that set but it has a great picture, works great and no one would ever know that it is a few kv short of what it really should be. so with this motorola set it has very low hv its affecting the width among other things and if the bright is up the center turns to fuzz then the whole screen turns to cotton, its got low hv, nothing i do will raise the hv as far as even a test. when the bright is up you can barely see the rectifier filiment but bright down that filiment is bright.caps are done i went over caps and resistors and much to my surprise as old as the resistors are in this set check very good so unless i am overlooking something then i still am thinking the fly may be responsible but again im not sure. but i will need to be sure in the end because there was no after market that made this fly, as per moyers in pa.

[ctc17]

It could very well be the secondary of rhe flyback is leaking between the two plates of the tubes. If the doughnut coil opens it will flow with carbon and eat up all the energy from the crt. Its hard to test without a ringer or substitute and because of the two tubes you can't sub anything in tthere. Does it get hot really fast? Run it for 5 minutes then turn it off and feel it. Does moyers have it? - have one of those sets here that has a weak crt but it only has one tube in the crt so its not the same. The egp crt is not very good

[timmy]

no moyers said an after market fly was never made and that it would have had to come from motorola itself.i did some crazy things to try to find out whats going on like the crt was not hooked up at all and the anode i left hanging and checked hv that way. when first turned on there is a strong smell of ozone in the area of the hv cage and the 2 hots but its gone after about a minute.i had it running one day for about an hour and the fly was hot but not burning hot, but the cathode current has got me baffled one moment its showing 220ma then another day it showed110 and 115ma. i kind of ruled out the crt as a cause, and the rec tube, and 6bk4 and that circuit and damper. i even checked resistors in the yoke and unplugged it but the hv went lower.well if something opened in the secondary, doughnut i think i would here hissing or maybe snapping but nothing really.the 2 horiz tubes test very good and appear new but maybe i should try 2 more. should there be any stray hi voltage around the ferite core like the probe of the hv tester, the point i get hv voltage from the core, by probing the point around the core, maybe this is normal.....

[ctc17]

That is radiation, what resistors did you recap the set with? Did you check or replace the small ones in the boost filTer area? The crt is the filTer cap for the hv disconnecting it will give inaccurate reading. You ssure you don't have the screens up way to high? Its not the tubes it sounds like its inefficient for some reason. The ozone is the same as cheap air purifier toxic gas that attracts cigarette smoke vut is there is liquid smoke from the flyback you know its bad for sure and you don't. Don't give up on it yet

[timmy]

resistors from top to bottom of chassis, all electrolytics were changed , all that are listed.i did the grey scale setup and the g1 master if it is down low there is no picture because then ill put the bright up and its all bloomed and out of focus. well i better put the anode cap back on then. well im not giving up and its good no smoke coming from anywhere.i did not change any fixed caps but i clipped one leg on a few key ones to check with an ohm meter set on 20 meg nothing jumps out at all. and still the sams says after setting the hv to 24kv then it says to measure 1.2 volts dc across r155, i get nothing maybe because the hv has to be up at 24kv. i guess its motorola they were different.

[ctc17]

the .1uf or .047 small ones in the boost and coupling will cause this problem more than the electrolytics.

[timmy]

would the .1uf be a disc and the other is a brown or red. well there are a few .1 and 0.1 disc caps and a few .047 and .47 that is in the area you are talking about so maybe ill get the values together and call moyers, and change them all. thanks

[ctc17]

disks dont usually go bad but they can short. the red ones get leaky, lossy or whatever. the white ceramic ones leak and explode. its best to purchase the proper tester off ebay rather than through parts inside it

[timmy]

the only white ceramic cap in this chassis is the big one that takes the ac in. this set has other issues as well like converging it the screen has the lines on the bar generator, the squares but the left side those lines are twisted alittle on the top mostly and the convergence on the same side is not right you can see colors overlapping just on that side the rest is fine so maybe a cap could very well be bad to do this, twist those lines and they are only twisted about a half inch but enough to mess things up. and i think the hv is the other issue.

[ctc17]

the lines may twist inside the screen if the flyback in not performing with the twisted lines for the pincushion transformer because some of the circuits on the convergence gets its voltage from the horizontal pulses. if the hv is not working right it will never convergence to adjusted right. you have to repair the main large issues because it all interacts with each other. even the vertical in most sets gets it power from the boost off the flyback so if thats low even if the convergence board gets it power from the vert out transformer it wont be right.

[timmy]

got 12 caps ordered from moyers might get them monday.