My First Predicta
 

I've successfully restored 2 Seventeeners that have similar guts but this is my first purchase of a Predicta. They don't come up for sale too often in my area. Holiday model in mahogany. Cabinet looks in good shape but the safety "plastic" looks pretty cigarette tar stained. I'll be picking it up this Saturday. I don't know the status of the CRT but that doesn't matter to me. I'll get a decent one from somewhere.

First hurdle. 21EAP4 tests strong at 2.4 volts with good cutoff. Happiness!

Could the seller have rejuvvied it before selling the set? Finding one of those jugs that's not flat is a rarity.

I don’t think so. He was not an electronics guy. Had the tv for a month after finding it cleaning out a house.

Chassis Removal
 

Flyback looks to be in good shape. Chassis is almost all factory except for a capacitor on the main circuit board and the fusible resistor has been bypassed. Pretty clean and looks like it's had modestly light use. If Bob A is out there, do you know of a resistor substitute for the fuse plugin?

I typically sub a fuse of the same current rating and a resistor the same or higher resistance and power.
You can still sometimes find NOS fusistors. I've found if the one in the set is good it'll typically stay good unless I mess something up, so if I find a bad one and I have a good replacement NOS I'll use the NOS.

Ah, but what is the current rating of the original? It's not in the service info.

The only thing I've ever found is this which rates them in wattage - not current. I assume 5.6 ohms at 5.6 watts translates to 1A. I've measured the B+ current in a few sets and it's slightly over 1A.

Watch this for suggestions on replacing them: https://youtu.be/hYDJZvHPM1A

https://live.staticflickr.com/65535/...4b92b818_z.jpg

Got it...thanks Bob and Tom. I can't find the startup thermistor on this one though. They're usually on the bottom of the chassis right? Hmmmmm.

Probably fell out. It happens a lot

You gotta hand it to Mr Rigotti. These are fantastic and a wonderful timesaver.

Got the shell and safety plastic off the CRT. I think the condition of the yoke provides more evidence this is a low hour TV. Nothing looking burned or full of dust...electrical tape still soft and adhered...plastic cover on the back of the yoke still pliable and no heat damage etc. Even though the glue on the label failed, the label itself is perfect and still glossy. The dag is perfect. I'm starting to believe more and more the CRT test on the Sencore showing strong emission with good cutoff is real.

At this point, there's no HV so the next step is to investigate that.

Chris

Some photos of the neck and its insides.

For no HV check power supply is good, H osc is working (look for sufficient negative grid bias on the output), make sure the paper caps in the horizontal are changed and that the width pot isn't open (or dirty enough to act open), and make sure the damper tube is okay. Once those are checked good if still no HV lift the HV rect top cap and try to draw an arc from it....If you get a healthy arc then the rect tube is bad, it's heater winding/heater limiting resistor is bad (open or shorted to ground) or the wire from the HV rect socket to the CRT is open or unplugged.

If no arc anywhere after all that report the control and screen grid voltages on the H output tube vs schematic. Screen grid voltage will tell you if the flyback is drawing power from the flyback and if it's got a partial short or open.

Thank you Tom! Will investigate as per your flow chart this evening and will report back!

What about the rest of the set? Are you getting anything out of the speaker? Can you tune a station in?

There is some static from the speaker but no change when the channel is changed. All tubes are lit.

Oh and Bob, it's been completely recapped...all electrolytics cut out and replaced with Nichicon caps and all waxies replaced. I installed new couplates from Mr. Rigotti's website. I guess I need to consider the possibility the TV suffered some sort of catastrophic failure, like a flyback short, early on in its use and was put away. That may account for what looks like, to me, minimal use.

The safety "glass" is another issue. The inside had the well described white powder residue. I've been using some fine automotive polishing compound and an electric buffing pad and it seems to be working but with considerable effort. It smells bad. I don't know if that's a common thing. It's also pretty dark. Do they yellow with age as well? I do know some plastic yellowing reversal techniques using hydrogen peroxide and UV light that I have successfully used on old computer equipment and vintage games. I would want lots of opinions and advice before I take any steps like that.

Chris

I changed the 1B3 out of another set that works and replaced the one in the Predicta but no change. I've got all of the B+ voltages...all maybe 10% low due to the age of the rectifier diodes that I didn't change. I'll have to look at the schematic as I can't get to the bottom of the H Osc socket, The choke or the VOT is mounted right under the tube and I don't have a test socket so I can check the bias. The resistor between the HVR and the HV lead to the CRT is right on at 5.5K and the HV lead has continuity. I did find something interesting as one of the wires going into the yoke chassis plug had pulled out of the pin socket but that's probably something I did moving the chassis around. It's been repaired.

They used tined plastic - do NOT try to chemical treat it. I've worked on about 200 vintage TVs at this point and have never found a bad flyback so that's the last thing I'd consider.

Yes, they smell - it's the Tenite plastic Cleaning them exposes fresh material and it will smell worse for a while. I've had good luck with ScratchX and Novus #2 plastic polish.

As for the CRT looking pristine, that's great, but not that unusual because the plastic shell protects them from the environment.

If you're not hearing anything when you change channels, you have at least one other fault - maybe related to the lack of HV like something is off with the power supply.

I always recommend the easiest thing first. Grab an ohmmeter and go through the resistance chart published in Sams. No need for socket extenders or an isolation transformer.

Everytime I've made a wiring mistake, I found it very quickly with this method.

One thing that makes this hobby more difficult than it probably should be...I am significantly colorblind. Resistors and bumblebee capacitors are very difficult for me to interpret and I rely on Sams chassis pictures, what the installed capacitor is labeled as and the parts list. Below is the only capacitor in the main chassis that I have not replaced. I can't see it in the small Sams picture and I can't find it on the schematic. It reads a very weak .015 and leaks at 25 volts. Can I get some help?

Thanks
Chris

Thank you very much Bob. I'll check the resistance readings

OK there is an issue with the B+ voltages in 3 of the 6 DC sources. There is no 260v C source, the boost voltage is 225v (should be 435v) and the 140v source is reading 41v. Sorry about that. Looks like there is an issue!

That's a 0.01uF cap rated for 600v

Thanks for the information and the translation on the bumblebee capacitor! In my CRT evaluation, I was referring more to the heat damage I've seen on yokes after prolonged use. Just about every yoke on an almost dead CRT I've come across shows obvious signs of heat related degradation. Plastic warped and brittle...applied tape dried out and burned...wires with heat baked brittle insulation...discolored ceramic capacitors and resistors etc. Nothing of the sort on this one. Do damaged or dead 21EAP4s test as good sometimes? I really hope that's not the case with mine. It tested with good emissions and cutoff on my Sencore at 2.3V

Keep in mind the 21EAP4s have a design flaw that resulted in a short life - less than two years. Long before the issues you mention show up. For example, here's a dead 21EAP4 and yoke that look brand new.
https://live.staticflickr.com/65535/...18d61651_z.jpg

No, it would not test good if it had issues. I'm not saying all 21EAP4s are duds or doomed to early failure - just that that had a high failure rate initially. I replaced this dead EAP4 with another that tested like new. It had no label - so I don't know who made it though.

I'm not sure which Predicta you have, nor have I had a chance to work on one yet, but they should be mostly alike, found this, so.

http://www.earlytelevision.org/pdf/p...sams_439-1.pdf

Obviously the missing voltages are the first task.
No 140v = no IF, thus no video/ sound.
No 260v C will kill the horizontal oscillator/ HV, and thus you have no boost and it will be at low of 200v ish.

Looking at THIS schematic anyway, there has to be something really weird wrong for 260v C to be missing, without that, the cathode of the audio output will be all wrong, and thus 140v will be wrong as well.

That's the Sams I'm working from. I see what you're saying about Source C and the 140v. I'm not all that great with schematic symbols...is there anything significant to that X on the line between 260 B and 260 C line right next to the .047 capacitor designation? Could resistor R75, the 18K 2 watt be an issue? I'm going to replace the rectifier diodes anyway but I have 250 v DC coming out of them and not the 280-290 V that should be there.

An x / broken line ( so on ) indicates an optional way of the circuit being wired, depending on run / make/ year / model.

Thank you...so if the model I'm working on does not have that jumper, could issues with the resistors I mentioned be a possible source of the lack of voltage on C and half the voltage on the 140v source?

+/-20% on the voltages is fine. They are very much dependent on your input line voltages and the operating points of all the circuits, condition of tubes etc.

Like I said, go through the resistance chart. There has to be a major smoking gun (or two) for voltages to be completely absent. It's not going to be something off be a few percent - it's going to be an open circuit or something shorted.

I've started to. First I checked all the wiring from the AC line to the line filter cap, through the diodes, through the choke and the electrolytic caps that bracket it. It all checks out so that means I didn't screw up those first 3 electrolytics.

I started with V1, first tube in the chart and the first video IF tube, a 3BZ6. Pin one should be 1.5Mohm and I have that. Pin 2 should be 47 ohm and I have 65 ohm. Pin 3 should be 14 ohm and I have zero. Pin 4 should be 15 ohm and I have zero. Pin 5 should be 330 ohms measured from the 140v source and I have 420 ohm. Pin 6 is the same measurement parameters as 5 and I have the same 420 ohm. Pin 7 to ground should be zero and I have 0.1 ohm. Looking at the schematic, I don't see pins 3 and 4 connected to anything so I don't know what these mean. I really apologize asking you to take me by the hand but is there a tube in a different section I should check that would help figure this out faster?

Thanks Bob

3 & 4 are the tube filaments. I wouldn't worray about them since your tubes are lighting up. I suggest checking the 12CA5 audio output tube and the 12DQ6 horizontal output tube.

Oh of course they are. Duhhhhhh! Anyway thanks for the guidance. I’ll check back in to the board once I get more data tomorrow night

Since it does not have the direct link as you mention for the 260V C, but through the unnamed 2.2k resistor ( current limiting? ) , doing as bandersen suggested should find the problem, be it a short or whatever, if it IS a short, the voltage drop across that 2.2k resistor would be rather large, and it's prob getting a bit warm!

Happy Friday all and Happy Friday Bob!

I'll keep this simple. I'll state the tube and the readings will go from Pin 1 to the last pin sequentially. I won't give the pin number for clarity sake. I'll list the resistance readings as measured/should be. All were measured from chassis ground except where indicated otherwise.

12CA5: 96/68 0/480K 0/12 0/14 530K/480K 1100/1000 295/295

12DQ6: 0/0 12meg/22 0/0 192k/9k 1meg/1meg 500k/Tie Point 20/20 3/0 15/25 (Top Cap)

To me, the 260v C voltage isn't getting to the 12CA5...but I'm kinda lost! Any thoughts? I'll remeasure to be sure.

Well some of those readings are way off. I'd start by tracing out the 12CA5. Is pin 2 grounded accidentally? Pin 2 and 5 should be connected together so you should have gotten identical readings but you didn't?

Also check that the primary on the audio output transformer is good. That supplies the plate voltage to the 12CA5

Audio output primary is good, 285 ohms. The reading on pin 2 is correct at zero. Checked several times. I thought I might get away with not removing the board but it's looking like I might need to.

So I pulled the board. At some point, the socket for the sync sep was replaced. Lousy job too. All the pins have continuity with the traces on the board except pin 2. In fact, the board is so discolored from flux and heat, I can't even see where it goes. In the schematic, pin 2 is the screen of the 9BR7 and it feeds into the K2 couplate. I do not have continuity between the pin 2 solder tab and the tab just to the right and above which would be the more likely candidate for continuity...again, the board is so fouled, I can't see if that's the case. No problem jumping the pin to another spot but I don't want to jump to the wrong spot. Anyone have any ideas?

That's the 10DE7. There is no connection to pin #2.

I better stop embarrassing myself and taking everyone's time. I'll dive into this over the next few days and see where I can get. Thanks everyone.