Predicta has raster, sound, but no picture
 

Just started working on my 17" Predicta Debutante. This set has been in our family for about 25 years or so now... Was working OK when put into storage about 20 years ago. Started out by testing all of the tubes on my TV7-D/U and found them all within spec. :yes: Then pulled the chassis and cleaned most of the dust and dirt --- it was very nasty! Replaced the chassis and all tubes (except for the horizontal output tube) and brought it up slowly with a variac. Heard a bit of sound from a strong local station, so I decided to power it up again with the H.O. tube. With a little fiddling of the controls, I now have a nice and bright full screen raster. :thmbsp: Am also getting sound on two local stations (with a lot of hum), but no picture....

I found a few signs of prior servicing. One of the 9-pin tube sockets has been replaced and most of the paper caps on the main board apprear to have been changed at some time. Kind of crappy workmanship on these repairs, but look OK for now. Everything else looks untouched.

I'd welcome any advise as to what to do next. Where should I be looking for a problem with no picture, but good raster and sound? Since I have sound, wouldn't this indicate that the tuner is functioning properly? Should I be happy with the results of my first testing and plan to proceed with recapping? Any known trouble-prone components in this set that need to be addressed?

My plans for this set are to make it safe for occasional use. Would be neat to be able to demonstrate it with some vintage programming via a DVD or VCR.

Thanks!

I would look at the video detector diode and video output stage.

Connect the video lead from the picture tube socket to the PC board.

Don

Right on! I'll bet that's what his problem is. That lead is easy to overlook. Its a solitary lead with a simple pin socket on the end.

All of that wiring is solid rigid unlike multistrand and can break off if flexed excessively.

A set I restored sevearal years ago had several broken wires to its' name by the time it had been shipped to me.

I've had to build up a couple of those flat monolythic component units too.(Sync Circuit?) Simple resistors and caps.

They produced a good picture when everything was right.

I've heard that these had flyback failures over the years, but I never saw a bad one.
I'd like to think that by now those that were destined to fail have done so.

Best Of Luck With Yours !!

Bob

Well, you guys hit the nail on the head... It was the single lead that plugs into the video out pin on the main board! :thmbsp: I don't recall disconnecting that lead. But, it may have disconnected when I pulled the chassis. It's a tight fit in there!

Now have a pretty fair picture and good sound:

http://members.cox.net/wlcarroll/predicta.JPG

The picture is not as dim as pictured; it washed out a bit when I photographed it. However, there isn't much contrast and the picture does tend to roll occasionally. Plus, the images are "taller" near the top of the picture, but not too bad.

I want to go ahead and proceed with recapping the main board and also the multi-section electrolytic cans. Also just sent the original speaker off for reconing.

Any tips on cleaning the tuner?
Should I replace the 5.6 ohm resistor/fuse? Seems that this is a common problem with the Predicta?

I welcome any other tips from the experts out there as this is the first vintage TV I have undertaken. I'll be glad to update this thread with more pictures as I progress. Thanks!

What's the chassis number?

Don

Don, I think the chassis number is 10L43. I'll double-check tonight.

Thanks,
Wes

This looks like the same model I have. I just pulled it out the other day. I had previously replaced a few of the caps in the vertical circuit due to insufficient height but it still wasn't right. I had to pull the chassis loose and replace one more and that did it. Unfortunately the crt on mine isn't real strong. With the normal/fringe switch turned to, I think, normal, the faces tend to go shiny and negative. The tube chart has the crt # crossed out and another one written in so I guess it was swapped, but that was long enough ago for the replacement to wear out as well. I've heard these were "motel specials" and I'm pretty sure mine is. Anyway, for no more than I use it I can't complain.

I wouldn't worry about the fusible resistor unless it goes bad. I got my set cheap because the old one was shot. I had rigged up something with some new resistors but then I found a NOS part.

Wes:

On the 10L43, vertical problems usually come from:

Bad .0015 at 1KV - feedback cap
Bad .1 at 400 volt - coupling cap
Bad 6DR7 Tube
Bad Height Pot
Bad Vert Lin control
Bad .0068 at 400 volts - discharge cap
Bad .022 at 400 volts - Buffer
Bad 30 6030-7 RC Integrator network
Bad 1.5 meg plate resistor
Bad 30-6509-1 coupling network
Bad 100K 1Watt resistor - Buffer
Bad Tube socket

In the order listed

Leave the fuse as is. When it goes bad, you'll know.

Clean the tuner with any standard tuner cleaner. Just spray it in , rotate the tuner a few times and let it dry. Aim for the switch contacts. Lube the tuner detent with Lubriplate or a small amount of white grease.

Don

I was bit by the video lead when I restored my Predicta barberpole ( http://antiqueradio.org/philc12.htm ).

Looks like you're making good progress. I would definitely replace all remaining paper/plastic/electrolytic caps while you have it apart. There's nothing I hate more than having a "restored" set conk out because I was lazy the first time around.

Thanks everyone for the tips. I've made a little progress on the Predicta... All of the electrolytic capacitors have been changed. This was quite a challenge since the originals were multi-section can type caps and the replacements are Sprague Atoms. Terminal strips were attached to the chassis to mount the individual capacitors:

http://members.cox.net/wlcarroll/chassis.JPG

Powered up the set, and it seems that I have a worse picture than before. :thumbsdn:

The image near the top of the screen is still squashed... even worse than before. It is concentrated into a band that is about 2" high near the top. Also, the picture will not quit rolling. If I adjust the controls to stop the rolling, it will be OK until the scene changes, or a commercial comes on, etc. and then will start rolling again.

Here are some pics:

http://members.cox.net/wlcarroll/pic1.jpg
http://members.cox.net/wlcarroll/pic2.jpg
http://members.cox.net/wlcarroll/pic3.jpg
http://members.cox.net/wlcarroll/pic4.jpg

All of the original paper caps have been changed by a previous owner. They look similar to orange drops except they are purple in color.

Any ideas of where to start checking?

Thanks!

I think those purple looking caps are original, don't think they've made those for a while so I'd go ahead and replace them.
Start with the ones around the vertical output tube and see if it doesn't improve the strech problem.

Eric is right... even though they've already been changed, change them again. There's been plenty of times that I've left caps in that had already been changed in the past... but come to find out they still needed changing. Unless they're actual orange drops, it's probably best to swap 'em out.

Good luck!

Looks like height and lin controls are misadjusted. Can you reduce the height control so the picture does not fill the screen and then adjust the lin to stretch the top?
Don

Readjusted the height and vert. lin. pots. Things look much better now. :thmbsp: Also cleaned the tuner and the tube sockets. This helped with the overall performance of the set.

The picture still "rolls"... If I adjust the vertical control, it will stop rolling for a few seconds, but always continues to roll. Is this a problem typically caused in the vertical output section?

Getting ready to order some orange drops... Looks like a real pain to change the caps on the pc board. :sigh: A previous tech soldered most of them to the leads of the original caps. I can see why he did this! It's nearly impossible to get to many areas on the pc board from underneath! :no:

You need to desolder all the leads from the board, as well as the tabs holding the board to the chassis, and remove the board to service it properly.

There is a website from a member here I believe that has good detailed pictures on his philco restoration. Definitely worth the read:

http://antiqueradio.org/philc12.htm

Once you go thru the caps (and also check the resistors) in the verticle section, you'll fix that roll. If memory serves, there's probably one of those damn combination-components in the verticle section. It's a tan rectangular flat piece with several leads on it... it's made up of several caps/resistors. Those usually go south. Sams will give you a schematic of it on the main diagram page. If you get the caps and resistors, and follow the schematic, you can build one to replace the original. Just gotta make sure you follow the diagram carefully. Make sure you number the leads that come off the end result so that you'll plug 'em in the right spots. I've built a few for some of my sets with really good results. It's just a little time consuming.

Yes, that's my Predicta restoration article referenced above. It describes removing the board. It also has a little discussion of replacing one of the couplates ("those damn combination-components"). My homebrew replacement isn't gorgeous, but it was easy to make and works fine.

Well, I went ahead and replaced the four capacitors in the vertical section as recommended by Don and others. Also checked the two resistors mentioned and they test within spec. Can't see that it made any difference. :no: I may have to build the K5 couplate next... :scratch2: I suppose the rest of the main board caps should be changed first.

But, another problem has started which has been getting progressively worse. Periodically the set will lose all horizontal output momentarily.... The picture collapses and then immediately starts to come back. When this happens, I hear a "click" sound from the high-voltage cage, presumably from the flyback transformer. I've tried watching carefully when this happens, but can't see any arcing, just the the "click". Started out only happening once or twice in a troubleshooting session, but now it is about every 15-30 seconds.

Does this sound like a flyback problem?

Thanks for all of the suggestions so far, I really appreciate it!

Wes

I have some NOS couplates. Do you have a part number?

Don

Yes, I would bite the bullet and replace the remaining caps on that board. As long as the board is out, you might as well rebuild the couplate, unless you can reliably confirm that all its components are good.

Re the spark, I would check any/all other little components in that cage -- resistor, cap, etc. I don't recall offhand what's in there, but there might be something.

Reason I mention that is that I'm working on an RCA 630TS which had a burned resistor underneath the little phenolic board holding the 1B3GT tube in the h-v cage. More or less impossible to spot the spark, even in a dark room, but after I replaced that resistor, the Bzzt went away.

You probably know this, but I would not run the set for long periods until you find and fix the Bzzt source :-)

Don, The part number for the K5 couplate is "30-6509-1". Please also check to see if you have K4, which is the "vertical integrator". It is Philco part number "30-6030-7". Thanks!

Phil, I am going to attempt to do this... It is going to be a real pain to get into the high voltage cage. It looks to be as unserviceable as the rest of the set!

Not to be a wet blanket, but I thought the capacitors inside those couplates were paper -- which might mean that a NOS couplate would be as bad as the one you're replacing. If there's any way to check those caps with a capacitor tester under the right voltage before installing the couplate, that couldn't hurt.

Re the h-v cage, my Predicta is a barberpole and the stuff inside the cage is all quite accessible. Made doubly easy because the cage cover on my set is missing :-) Things may be different on your chassis. I have never worked on one of those.

Turned out to not be so bad getting into the HV cage. :thmbsp: The black coating on the flyback is cracked and crumbling. There are several chunks of the coating missing from the bottom:

http://members.cox.net/wlcarroll/predictaflyback.jpg

Would black RTV be OK to re-coat the flyback? Also found two resistors --- one of them under the horizontal rectifier socket as Phil predicted. The other can be seen in the picture above. I will replace them while in here. I don't really see anything else in here, except some dirt and dust that will clean up.

Also, I want to replace or repair the HV lead that runs to the picture tube. There is a previous "fix" to the insulation with some electric tape. I'm sure this tape isn't rated for high voltages... Any suggestions here?