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#1
08-27-2021, 10:45 AM
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My Predicta crapped out
Howdy All,
Well, tragedy struck last night. We were watching "What's My Line" on the Predicta Holiday and the picture was a little unstable. No adjustment helped. It was just jiggling, it didn't seem to be the horizontal lock. I have noticed a little occasional jiggle over the last few months, now that I think about it. The jiggling got worse and then *poof* we lost picture. I can't say if we lost sound because we have been running the sound through the stereo and I was on my feet and hitting the power off as fast as I could. This morning I tried turning it on. It has a picture, disturbed as it was last night. I am guessing if I left it on it would go dark again. Sounds like something is getting warm. The set smells fine, no hot smell. Some background: I "restored" this set, finishing about 4.5 years ago. "restored" is in quotes since it was my first and only TV that I have worked on. "Got it working with the help of this forum" might be a better description. It has been recapped, new tube sockets installed on the PCB, new couplates, new diodes, replaced the fusible resistor. It has been working fine for years with hundreds of hours on it. I am hoping for some help with troubleshooting, I am not an expert and my theory is weak. Many thanks in advance! 
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#2
08-27-2021, 01:44 PM
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You may have encountered a random failure of some part you did not replace in the last 4 years, you did real well for a Predicta.
 Anyone could assume the worst-case: flyback arc-short is possible as I have witnessed color sets behave this way prior to losing HV for good, which yours didn't, fortunately! But shorted turns (AKA internal spot-welds between adjacent windings) never fix themselves. Your HV came back because whatever part was failing decided to heal itself on a cold start. Get some freeze spray after all the parts around the horizontal oscillator. I am assuming H - jitters caused by H-hold or H-range pots being dirty or having tin-whiskers. I hope its that simple for you. There are some Predicta-savvy techs here, but I avoid THOSE Philco products myself. Most all us Philco-techs would agree: OEM Philco caps/resistors/pots are all SUSpect until confirmed otherwise  !
__________________
"When resistors increase in value, they're worthless" -Dave G
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#3
08-27-2021, 07:06 PM
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You are enjoying the true vintage Television experience of having your set die mid program, just like it was back in the day.
 Reading your description I wonder if it has a bad tube in the Horizontal section, oscillator or output. You might tap around on them and see what happens.
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#4
08-27-2021, 08:41 PM
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Eric H., you reminded about one of my TV repair customers in the mid 1960s. You will remember that at the end of every show Red Skelton would look into the camera and say, "Good night and may God bless." My customer was watching that show and the instant after Red uttered those famous words, the screen went black and a puff of smoke came out of the back of the TV. Flyback!
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#5
08-27-2021, 11:28 PM
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If it repeats that you probably want to have meters on the grids (G1 and G2) of the h output, and possibly meter the HV.
I few weeks ago I had something similar with a CTC-25. I powered back on and it was fine for a bit, then a few sparks flew inside the output and as the HV faded the damper began to redplate...Next power up it was dead and the output wouldn't light in my tester....The output base cracked and it had filled with air (hadn't had enough time to get white getter yet).... Surprisingly the damper was fine and with a new output it was happy as a clam. I've got 3.5 of the Predicta tandem/penthouse model on my bench right now. One of the 4 is necked and I'm going to be hard pressed to make 3 very nice cabinets out of the 4. Three chassis have life so far so once I work out the kinks I should have a keeper and 2 flips. Not sure what to do with the last one, build an extension cable for the HV, try to make a color set out of it, keep it for parts, or sell it cheap?
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#6
08-28-2021, 09:56 AM
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Pulled the chassis out and ran the set again. All seemed normal. I wiggled tubes and aside for one in the IF that needs the socket cleaned, no problems. The picture disturbance was the same. After about 10 minutes the screen went dark. No hot smell, noise or any sort of drama, just poof. The flyback was cool and no evil smells.
The TV and the work bench are in different houses so I will have to grab some meters and come over and check voltages. I do have an HV probe, not a great one but it will give me an idea. I will do as you recommend Tom. Will be next week before I am back here, I live a nomadic life and only spend 2-3 days a week where the set is. If I have to drag it back to the house with the work bench I will but I sure hope not. Not only will I have to bring the set but also the RF modulator and all that jazz. I have been meaning to get some sort of test jug so I could just bring the chassis. I also have a spare chassis I would like to restore, then when this sort of thing happens I can just slide the other chassis and take the other to the bench. Any other simple things to check?
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#7
08-28-2021, 04:41 PM
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Does it have high voltage after it goes dark?
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#9
08-29-2021, 03:45 PM
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If you put the tubes on a tester let them sit for a while and see if they change readings and also at this time check for shorts.
When the set goes out are the filiments still lit? My stab at it Thermistor going open once it warms. Sand resistor goes open when warm. Weak solder joint in a area that has higher current or high heat. The way you described the flickering I wonder if you're losing horizontal oscillation, and in turn losing horizontal output, HV and B+boost. I would start it back up and see if the filiments go out, and if they stay lit move on to the horizontal section.
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#10
08-29-2021, 05:59 PM
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I assume loss of pix means "went black". Almost always thats loss of HV.
Easy first. There are 4 tubes that will cause it. Hoz osc, hoz output, damper, & HV rect. I have never seen a HV rect go int. so leave that out. With the set running lightly tap the tubes & see what happens. This is usually better than a tube tester for this type fault. You can also do it on a checker to smoke out an int tube but having the TV raster works BEST ! Freeze mist was mentioned also. A real life saver sometimes. Best way to use it is spray it on a Q-tip & touch it to suspect parts one at a time. It will almost always be a cap. BUT keep in mind if you chill down some caps to much they will drift out of tolerance & act up but still be good. good luck 73 Zeno  LFOD !
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#11
08-31-2021, 10:51 AM
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Thanks for the help!
I am at work for a 72 hour shift but should be back to the set on Friday. I will bring meters and an HV probe. I will try the tube tapping, I did wiggle them. The filaments do remain lit when the screen goes dark. Sand resistor has been replaced when the set was restored. The thermistor is new but you never know so I will check it. I think there has been a progressive deterioration. It started with some screen jiggle a few months ago. The first time it went dark we had run it for 20 mins or so. Last time I tried it took 10 minutes or so. I have plenty of spare tubes so when I go there this week hopefully I will find the fault or at least gather some more clues.
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#12
09-02-2021, 04:32 PM
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Finally where the set it. Now when I power up I get nothing.
Swapped out V8, V10, V11, V12, V13. No change. The horizontal output tube looks like it might be red-plating a little but I am not sure. It is just a dim orange. Voltage at the rectifiers is a little low, 247 instead of 290. I couldn't find my HV probe before I came over to where the set is. How did I misplace something 12" long with a cord on it? I dunno. Anyway, I measured the flyback resistances and all are exactly as they were when I restored the set. What do do next? I guess start trying to track down the low B+ voltage. I think I have a test socket I can put on the horizontal output tube and do some looking at the voltages there.
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#13
09-03-2021, 03:24 PM
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Voltage is seriously low. Look at power supply first.
Next check the voltages on the hoz output tube. DO NOT measure the plate cap ! The G-1 voltage is most important. It needs to be very ( see manual) negative. If not look to the Hoz osc stage. 73 Zeno LFOD !
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#14
09-03-2021, 04:31 PM
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Quote:
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#15
09-03-2021, 06:24 PM
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True. I tend to assume OP hasnt had 40+ yrs in the entrails of a TV. So
I try to keep it simple & safe, one step at a time. In a perfect world the OP, TV & me would be all in one place with a great parts stock & the best of equipment. Without that its a challenge for all of us to help. 73 Zeno LFOD ! Quote:
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