Predicta Tandem / Penthouse scored - Page 4 - Videokarma.org TV - Video

bandersen · #46 01-09-2014, 12:41 AM

I checked the push on/off power switch for continuity and wasn't surprised to find it's flaky. I have to push it in firmly, hold for a second and release slowly to get it to stay on. Luckily my supplier has some NOS replacements left

bandersen · #47 01-09-2014, 10:09 PM

I'm done working under the chassis. Next up, I'll reinstall the flyback, hook up a CRT and attempt a power up. I'll have to clear off space on the workbench and squeeze in the 21" CRT unit and 25' foot cable. Not exactly the most convenient setup!

I noticed they have one side of the AC line goes all the way from the chassis AC plug down one 25' wire to a safety interlock inside the CRT and back down another 25' wire. So the set is effectively always running on a 50' extension cord. I assume that's a safety feature so the set can't be turned on with out the CRT plugged in. There must be some losses associated with that setup though. I'm almost tempted to short it out in the chassis.

VintagePC · #48 01-10-2014, 11:05 AM

Quote:

Originally Posted by bandersen

I'm done working under the chassis. Next up, I'll reinstall the flyback, hook up a CRT and attempt a power up. I'll have to clear off space on the workbench and squeeze in the 21" CRT unit and 25' foot cable. Not exactly the most convenient setup!

I noticed they have one side of the AC line goes all the way from the chassis AC plug down one 25' wire to a safety interlock inside the CRT and back down another 25' wire. So the set is effectively always running on a 50' extension cord. I assume that's a safety feature so the set can't be turned on with out the CRT plugged in. There must be some losses associated with that setup though. I'm almost tempted to short it out in the chassis.

Who knows, that extra 50' might contribute enough of a voltage drop that you don't need to do anything to go from 125 at the wall to 117

bandersen · #49 01-10-2014, 11:19 AM

OK, here we go! I ended up having to put the chassis on a box I'd have clearance for the CRT cable.

First, I check for continuity at the AC plug when the set was turned on. I got around 500 ohms which seemed reasonable.

Next, I powered it up without the fusistor installed just to make sure all the filaments would light up.

Finally, I popped in a NOS Workman 7.5 ohm fusistor, crossed my fingers and fired it up. After a little warmup, I was treated to a raster

I really didn't expect that on the first power up!

Now for the bad. No sound or video is getting through. No response at all to changing channels. I did the obvious things like wiggle the tuner and IF tunes and checked the connections, but no response.

I'll try injecting signals with a B&K 415 at both the input and output of the IF module. I've never even popped the cover off it so there could well be something wrong with it.

bandersen · #50 01-10-2014, 01:17 PM

Injecting a composite signal directly into the main board produced this. Funky video and the sync was non-existent. Probably the signal needs to be inverted but there's no polarity switch on the generator.

Injecting an IF signal into the front end of the IF strip proved more successful. Stable video and some sound.

I also tweaked the vertical height and linearity.

So the problem seem to lie with the tuner. Remember these were the only tubes that had been replaced. I'll do the simple checks first - swap out the tubes and check connections.

Kevin Kuehn · #51 01-10-2014, 01:51 PM

Looks like you're well onto the problem. FWIW your BK 1077 should have a polarity switch for the video out.

bandersen · #52 01-10-2014, 02:28 PM

Indeed it does, but I have it packed away up in the attic to make room for other equipment. I need a bigger workshop

bandersen · #53 01-12-2014, 12:52 AM

I removed the tuner and swapped in an identical one from another set.

Unfortunately, it made no difference

Of all the things that might have given me trouble with this set, I never expected it would be the tuner!

bandersen · #54 01-12-2014, 03:22 AM

I couldn't find any wiring errors and the voltages looked OK and I was running out of ideas when I had a thought about the tubes. Both tubes in the tuner are 9 pin and easy to mix up.

I had been using the tube placement chart in the Sams Photofact as my guide and it shows the 4BC8 RF AMP tube near the IF strip.

So I decided to take a look at the real tube chart in the Tandem cabinet. It shows the opposite

I'm just glad it's finally working and I didn't waste any more time on it!

The sound is excellent and the picture isn't too bad considering it's an original, nearly dead 21EAP4.

The brighter I make the image, the worse the focus gets. I believe that's typical of dying CRTs.

berta12 · #55 01-12-2014, 12:01 PM

Wow! Very impressive! I have a Predicata Tandem that looks just like yours and had someone fix it for me, since I'm not a tech.
Now I'm going to buy some orange goop and clean the cable (and the back of the TV where the cable hung for so long unless you or anyone could give me a better option for this) My Tandem is now fully operable--great picture and everything works! I need to sell it to someone who's looking for a Tandem that works well (probably use ebay) but I think I need to go with local pickup only, which would really limit the potential buyers, but even if I had UPS or FedEx pack it, I'm afraid that something will happen to it in transit. I would appreciate any thoughts on this, this you have so much more experience with vintage TV's than I do. Thanks and congrats on having your hard work pay off so well!

bandersen · #56 01-12-2014, 03:05 PM

I found Novus #2 Fine Scratch Plastic Polish to be very effective on the plastic CRT housing. I would avoid shipping these sets. I've seen several that were sold on eBay, damaged in shipping and the remains put back up on ebay to sell for a fraction of the original selling price.

berta12 · #57 01-12-2014, 04:46 PM

Thanks for the tip on the Novus. You also confirmed my gut feeling that shipping a set like this could end up in disaster. If no one buys it, I'll keep it. It's great to watch and to blow the minds of guests. And it's great company for my collection of antique radios. Thanks again for your help and your quick reply.

Electronic M · #58 01-12-2014, 09:08 PM

Hey Bob is this the first time a sam's typo messed you up?

I've had work bleeped up by sam's inaccuracies 2-3 times now...At this point if the set is different form the sam's in any way I automatically assume sam's is wrong.

dieseljeep · #59 01-13-2014, 09:29 AM

Quote:

Originally Posted by zenith2134

It's been fun to follow this restoration thread. When it's all done, I'd send the antique shop owner a pic of it running--people get a kick out of that.

Don't ever do that! Sending a picture of a set working well.
You'll never buy a set like that for a reasonable price. It's bad enough, those money-grubbers, consult the E-place and price their items, accordingly.
Most of these people, don't have a clue, how much skill and effort, it takes to restore a set of this kind. Also, the hundreds of dollars invested, beside the original purchase price.

dieseljeep · #60 01-13-2014, 09:53 AM

Quote:

Originally Posted by bandersen

I removed the tuner and swapped in an identical one from another set.

Unfortunately, it made no difference

Of all the things that might have given me trouble with this set, I never expected it would be the tuner!

]

I see Philco made their own tuner in that model.
The only Philco sets I worked on, that have a similar chassis, are the Seventeener II's.
I don't remember Philco using the Gated-Beam type of audio detector, in any other chassis.