Yet another Predicta Holiday restoration
 

Once again I've agreed to restore someone a set for someone else. This time it's a Predicta Holiday. After speaking a while on the phone, we decided all he needed to send me was the chassis. He;s got a 21FDP4 replacement CRT with a good filament so we're keeping out fingers cross it has some life left. He gave the chassis to his shipping department with instructions to pack it very safely.

It arrived in a giant box. Inside I found a big shipping blanket wrapped around a smaller box and inside that the chassis.

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Based on our phone conversation, I knew there were going to be some challenges.

First off, the HV cover and power switch - volume - contrast control are missing.
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The owner volunteered to track down those parts and has a lead on some already. Meanwhile, I've started work on the chassis.

There's evidence of earlier repair attempts. For example, the fusistor (which is open) had a piece of solder wrapper around it, the thermistor was jumpered and I have a wire to nowhere.

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Interestingly, the thermistor tests OK while the filament dropper is open. I bet someone noticed the tubes weren't lighting up and and went after the wrong part.

It also appears that someone clipped wires are parts so they could tip the main board on it's side. However, I can't really find any evidence that any work was done to it. Maybe they were just troubleshooting ?
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The electrolytics have been replaced but otherwise it appears stock underneath.
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On the positive side, the power supply choke, flyback and VOT ohm out good.

I decided the first order of business was to unmount the main board and get to restuffing it.
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Oh boy, here we go again....Bob, I notice you are no longer labeling the wire ends to the main board. How are you keeping track? Photo, color code referenced to pin numbers on the board, Philco diagram? I'll be starting my Princess in a couple of weeks, and I'd like to streamline my efforts as much as possible! :p:

Hi All;
If you look at Bob's Video, He says the He has reference photo's and Past Video's to guide Him, along with doing alot of these sets recently..
Good Luck Bob, You are the Man.. We will need to start calling You, Admiral Predicta Bob !!!
THANK YOU Marty

BTW, the Philco factory service manuals for the Predictas have very nice diagrams with labels, so you don't need to draw your own board diagram as I did once upon a time. You occasionally see an original manual for sale on eBay. There is also a guy who sells the complete Predicta set on CD.

Another advantage of using the Philco manuals is that the little numbers on the boards match the Philco part numbers in the manuals.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Good luck Bob! The official Predicta Repairman for the USA!!! :D

And thanks, Phil, for posting the factory board diagram on your website...That will be most useful:thmbsp: I know Bob has addressed this, but every time I look at that setup, I can't help but wonder if there isn't some kind of connector that could be soldered & shrinkwrapped to the ends of the board connect wires that could then be plugged/unplugged directly to the board studs...like a loose octal socket female pin?......something that would make good contact:scratch2:

Keep in mind the wires come off the board at a right angle near the base of the post. If you try using a connector, I doubt there would be enough slack to have it coming off the top. It's really not that bad to remove them anyway. It took me less than five minutes to get that board out.

Well, I was really thinking it would be nice to be able to install & remove the board more easily for progress testing, ....you know, recap, re-install and test.......but if I just go ahead and rebuild it k-nets, resistors and all like you do, Bob, it's probably extra work for nada!

Hi guys,

I have a Holiday that I'll start working on soon, the metal work is at the electroplaters and the original CRT (21EAP4) luckily has good emission. Although I used a far more clunky method to repair my 17 inch Predictas, I have ordered a set of grasp type test clips like those used on the CR-70 CRT tester. The ones you use when you don't have a socket to fit the CRT.

I'm planning on connecting wires with alligator clips to them. The idea is so that I can easily power and test a recapped Predicta board before desoldering it back onto the chassis. The grasp clip end attaches to the terminal posts on the board, and the alligator clip end connects to the (now floating) wires on the chassis.

For the less experienced like me, it seems like a good way to go, especially to save the trouble of removing the board a second time to tweak something after it's been soldered in.

Hope this helps someone!

Cheers,

Adam

Unfortunately, there is no quick & easy solution to the problem of connecting the main board to test it under power. In my Siesta article at http://antiqueradio.org/PhilcoH3412L...Television.htm you can read about my investigations into permanently installing quick-disconnect connectors. In the end, I decided they would create too much clutter. Using a bunch of clip connectors for the temporary hookup might work, if you don't mind investing the time & money for a bunch of connectors you may never use again.

An alternative is to do a very thorough restoration of the board while it is out, checking every single resistor, and so on. The disadvantage is that you are replacing a large number of parts with no opportunity to test the TV along the way. Sometimes the symptom caused by an inadvertent miswiring can be very puzzling to diagnose. Classical diagnostic methods (understandably) take the approach that you're trying to locate a failed part in a TV that is correctly wired. If you accidentally wire the neck bone to the ankle bone, so to speak, the symptoms may be rather bizarre.

Be aware that the board has multiple, separate ground connections to the main chassis. There is no single "ground" shared by the entire board. These separate grounds are made through lugs on the main chassis, and they are sometimes troublesome. On one of my Predictas, I added a ground line connecting all of the grounds on the board, to minimize this problem.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I'm making new networks with perfboard this time. It's faster and easier I think.

Here's the vertical integrator.
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Once completed, I double check my work, heat it a while to drive out moisture and encase in epoxy.
Those little blue caps are 630 volts C0G type ceramics which are somewhat expensive but very temperature stable.
If I end up doing many more of these, I'll consider have little circuit board made and use surface mount parts.
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Almost done with the main board which has warped a bit. A damaged 7-pin socket and all four 9-pin sockets will be replaced. Four sockets done - one to go.

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Very nice work, Bob.

Nice work, Bob.

It's always interesting to see you think up new ways of doing things. Did you rebuild the couplates because they were faulty or because you will be far more confident with the restoration? Surface mount components is a good idea... how do you fit these? Machine, tweezers or just great eyesight and care?

Nice work on those networks, Bob. Man they look tricky! :D

When I work with surface mount parts I use tweezers and a lighted circline magnifier similar to these.
http://www.dazor.com/illuminated-magnifier-lamp.html

That works for me as long as the resisters and capacitors are no smaller than 0603 size. For TV work you would want to use the larger sizes anyway because of power levels.

Hi All;
If you look at Bob's previous Predicta Video's.. He has many previous network, how to do video's and the steps for doing them.. As well as improvements on the process..
THANK YOU Marty

Yes, except that I made these using a different technique. Before I used perf board - this time I tacked them together in free space.

I've worked with small parts for years and my eyes are still god enough so I found this fairly easy.

The couplates that look like a bunch of vertical tubes are really made up of carbon comp and ceramic caps. I've measured a bunch and the resistors are have typically drifted high.

The flat, thin couplates like at the top of my photo are made using material deposited on a ceramic substrate and measure more closely to the specs. So I suggest leaving those alone unless you know for sure they're bad.

As for SMD, I've seen various techniques used. The most basic is to dispense the solder paste with a syringe, place components with tweezers and "bake" the board to melt the solder paste.

More recently, I've seen board vendors supply a laser cut sheet metal mask so you can squeegee all the solder paste on at once. Like silk screening.

Yes, typically when boards are manufactured they use the silk screening technique and solder all the parts at once. You can do it by hand one at a time by placing a small blob of solder on one pad first, then re-melt the solder while placing the part. After that you solder down the other terminal(s).

You can do the silk screening technique by hand too. Here's a good tutorial: http://youtu.be/qyDRHI4YeMI

My parts arrived and I finished with the main board and modules.
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I also cleaned up the icky, sticky wires with denatured alcohol
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Next up, under the chassis...

Hey, Bob.....I really like the new k-net treatment :yes: ....looks to be much easier than the perfboard assembly, and once they are glued up and painted, should be fine....after all, we are not spliting the atom here, are we!:smoke: Thanks for allowing us to check out your work!

The board has been re-installed without incident :)
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I also figured out these loose wires went to the now missing AC switch. I'm going to just short them together until a replacement arrives.
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I got a princess chassis on the way, was planning to have it as a backup, but I think I may do the full restoration treatment ala Bob. Since its not for a current working set I figure I do not have a lot to lose, this way I can just swap a chassis out if need be.

Nice work as always Bob :thmbsp:

Thanks and I'll be doing a Princess soon too. It's the first vintage set I ever tried to restore a few years back but stopped when I realized I needed more experience on easier sets first.

BTW I saw your posts in the ARF classifieds - glad you got that straightened out.

yea man I could not believe I pulled such a bone head move to send the money to some random Ebay. I was really glad I got it back so quickly.

I replaced the filament dropper with three Dale power resistors. The thermistor was replaced with a couple Ametherm 220 ohm in series to simulate the 400 ohm original.
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I stuck a 15 ohm resistor in the CRT socket to simulate it's filament.
Success :)
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Thanks again for this very useful info, Bob.

You're wetting my appetite, I can't wait to start mine! Luckily I have sourced all the needed cosmetic parts to finish the 17 inchers. Now I'm just waiting on the players to do their bit. One question remains: to powdercoat or not to powdercoat... I'm not sure how I'll reestablish the lettering on the top of the cabinet where it says Brightness etc...

Cheers and well done,

Adam.

I finished with replacing the paper caps and resistors under the chassis. All the electrolytics too, but some are temporarily tacked in. I'll do a more permanent job once the set is working.

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I'll be powering it up without the CRT using a power resistor in place of the filament.

Hmm, only 75 volts at the output of the filter choke. Should be around 300.
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Eventually, I traced the problem down to the voltage doubler diodes. My DMM's diode check function showed them as good, but a 0.1 volt forward drop didn't seem right.

Sure enough, when I tacked in a couple temporary 1N4007, B+ came right up to where it should be, I got sound out of the and hear a high pitch from the horizontal circuit.
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Finally, I popped the CRT off a restored Holiday set and got a raster :banana:
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Even better, I can tune in a station although the vertical is messed up.
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After adjust the vertical linearity and maxing out the height, I'm almost able to fill the screen. Also the vertical hold is very touchy.
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The replacement control arrived and it tested good so I installed it. Power. volume and contrast are all working correctly now :)
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I then went through the vertical circuit and everything checks out. For example, here's the vertical sync pulse at 2 V p-p just as indicated. So although it's a little touchy, I think it's working as designed.
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I'm going to let it run for a while then ship it back to it's owner. I sure hope he's able to wire it up to his CRT and get it running at his end.
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another great job Bob. Now on to the Princess!

Not so fast!

First off, I got a new tripod and better lighting on my workbench :)
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Next, I wasn't really happy with having the electrolytics scattered around the chassis. So I found an old cap of the proper size, restuffed it and restored the original wiring.

I also added another 10 ohms to the filament dropped to compensate with the higher line voltages encountered today.
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I also rebuilt the old dual diode assembly with modern diodes.
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Then the "fun" process of installing the chassis. Remember I was just sent the chassis. The cabinet and CRT are from my set.
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It played fine for a few minutes then the horizontal collapsed to a vertical line then disappeared altogether :( The sound is still good though.

I pulled the chassis back out and wiggled some wires. That seemed to fixed the problem at first, but after about 30 seconds it collapsed again. I pulled the chassis twice more with the same result.

So it seems to be an issue with a loose yoke connection or possibly over heating. I'm not so sure about heat though because once the problem occurs, letting the set cool down does not help.
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It was a pain to pull the set apart again, but I think I found the problem.

When the picture goes out, it collapses to a vertical line then quickly fades away. So I figure it must be an issue with the horizontal circuit.
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Sure enough. A scope confirms that although the hor. oscillator is running just fine, there's no signal on the 12DQ6 HOT grid.

After a little poling around, I discovered that putting slight pressure on the K5 hor, network in just the right spot restores the raster. I figure there's a cracked PCB trace or bad solder joint under that network.

I wedged a bit of foam against the network and the sets has been running fine for a bout 30 minutes now. Next, I'll pull the board out and fix it properly.

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When I restored my Siesta, I found the plastic cap from a Bic pen wedged tightly between the main board and the chassis. At the time, I wondered whether it fell there by accident or it was purposely stuck there to "fix" an intermittent connection on the board. The TV worked fine after I redid the board, anyhow.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

It helps if you remember to actually solder the leads :sigh:

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I know this already but sometimes forget and then have to "re remember", but I am adding to my check list is a good magnifying glass and strong light, and just go over the pcb/wiring as part of my normal check out.

I recently added some Xenon under cabinet "puck" lights. They get kinda hot but do kick out a lot of light and they're cheap :)

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Based on his performance of the miracle of healing upon a severely stricken chassis, I believe Bob should be canonized henceforth as Saint Predictia IV. :sing:

Well I don't know about all that :o I still have several Predictas to restored so we'll see.

I soldered up that open joint and reinstalled the board. The task was made easier because I happened to have another 9L37 chassis nearby for reference.
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Viola! It works and has been running for 30 minutes without any more problems popping up :)
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Bob,
Would you be interested in selling the round bezel + dial glass from your extra RCA 222 cabinet?

I sent you a email.

Thanks