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 Post subject: Trying to rebuild Philco Predicta Tandem
PostPosted: Feb Wed 28, 2018 4:40 pm 
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Joined: Feb Mon 26, 2018 12:39 pm
Posts: 1
HI everyone IM new to the forum. I recently picked up a Philco Predicta Tandem on eBay. The story behind the set is the woman I bought it from, got it from another woman who swore it worked but when she drove it to her house they couldnt get it to come on. I tested the picture tube and it tests well. So at least that is ok. When I got it I plugged it in and the tubes all l lit up, but I had no sound or video. Last night I tried to use my DVOM to test the output of the filament dropping resistor and the FUsistor and when I plugged it in nothing lit. Also the output of the filament dropping resistor is 119 volts on all terminals. I have the Sams photofact for the TV its sheet 441-2. At this point I am trying to figure out the next step in getting this tv working. Many of the resistors I tested on the main board were open. However the board is covered in dust and some sticky substance. Id like to clean it to make sure the filth isnt keeping me from getting a connection. What is a good choice for cleaning the board? I have some CRC Electronics cleaner I can take from work. Ive never restored a tv before but I have fixed other electronic devices, I can read a schematic and have very basic electronics knowledge from high school.
What I dont know is the school of thought when working on one of these TV's do you just replace everything on the board? Or do you test everything and just replace what is needed? I only see one leaky cap, but I assume they should all be replaced? What do you guys think?


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 Post subject: Re: Trying to rebuild Philco Predicta Tandem
PostPosted: Feb Wed 28, 2018 6:07 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 26442
Location: Detroit, MI USA
A 21" Predicta of any cabinet style would not be a good TV to learn on, they are extremely difficult to service and require physically removing the circuit boards from the metal chassis in order to properly replace capacitors, resistors, tube sockets and component combinations. You don't automatically replace everything, but you do automatically replace all the known failure parts that others have experienced over the past decades on the same chassis.

There's likely either a burned out tube, or bad socket not making contact with a tube, causing none of them to light since it's a series string. The first thing you need to do is get them to light, only then can you do further diagnosis allowing you to see if they were telling the truth about the working condition of the set. It's unusual to find an unrestored Predicta that works very well, but it could have worked somewhat.

This is a set where you want to try to get the screen to light at the minimum before tearing into it, so you have some idea that major components are OK. While that's not always possible, many times it is.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Trying to rebuild Philco Predicta Tandem
PostPosted: Feb Wed 28, 2018 8:20 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 837
Location: Southwestern,Ontario Canada
You might consider watching a whole lot of video's made by Bob Andersen on Youtube. He has quite a few (videos) on the Predicta line. You can check them out here:
https://www.youtube.com/user/bandersentv
He restores the various models of Philco Predicta's from start to finish. Watch and learn from the master. This should answer a lot of your question's as to if you are in over your head or not.
Tony


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 Post subject: Re: Trying to rebuild Philco Predicta Tandem
PostPosted: Feb Wed 28, 2018 9:46 pm 
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Joined: Aug Thu 20, 2015 3:09 pm
Posts: 726
Location: Albion, CA, USA
A Predicta Holiday was my first and only TV restoration. I did have a reasonable amount of electronics experience prior to starting. It was indeed a PITA but doable. I did as recommended above, did the minimum to get some life out of it (Open fusistor, replaced the electrolytics, bypassed the broken on/off switch and a few other things). Then I went through the whole thing. The PCB is indeed a pain to remove, 18 wires or so to remove and label. I replaced all parts on the board to avoid having to take it off again. Only had to take it off twice. :shock: I had the wife help me double double check all components and values as I did it and again before it was put back on. Look at the tube sockets VERY carefully, they are known to be an issue and that is why mine came off a second time. I left the IF board alone as I do not have the tools or know how to align it. The speaker cone is likely to be disintegrating, I used another speaker while sending off the original to be re-coned. Don't run the set without a speaker connected. And don't stick a soldering iron tip through the freshly re-coned speaker, you will use a lot of cuss words, at least a month's worth. Or at least I did. :oops: Get an original copy of the Sam's, much easier to read than a scan. The tandem's are very cool. They have one of the video tubes up in the CRT shroud because of the long wire to the chassis.

It works fairly well now. I have a few small issues that I will work on one of these days. However, I watch it weekly and really enjoy it. Watch Banderson's stuff FOR SURE no way I could have gotten mine going without his videos and help.


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