Yet another Predicta Holiday restoration

[bandersen]

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.



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.


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.



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 ?


The electrolytics have been replaced but otherwise it appears stock underneath.


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.

[bonanzaman]

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!

[Geist]

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

[Phil Nelson]

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

[bigaudioal]

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

[bonanzaman]

Originally Posted by Phil Nelson

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

And thanks, Phil, for posting the factory board diagram on your website...That will be most useful 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

[bandersen]

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.

[bonanzaman]

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!

[Down Under]

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

[Phil Nelson]

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

[bandersen]

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

Here's the vertical integrator.


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.

[bandersen]

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.

[ChrisW6ATV]

Very nice work, Bob.

[Down Under]

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?

[bigaudioal]

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