My 1st Predicta

[DaveWM]

fixing for a friend, only had minor issue, needed a new vert lin pot, the sectional cap for the vert out k bypass was open, so I restuffed it (also had some screen caps in there), left the others alone (doubler and filter b+ filter).

would not lock vert sync, had a very high sync tube plate load resistor. Other than that it was fine. The IF audio tube was weak, and has an intermittant socket (guess that is it the tube has a sweet spot that make it work). I checked the HOT K current its in spec at 100 ma as long as the screen is set to the min to just fill out the width. The HOT had -35v on the grid, should have been -45v, tried swapping out the tubes little change.

checked the grid resistance it was high, SHB 700k was 1.2 meg. there are 3 resistors that make up the total. I decided to leave it alone since the only way to fix is to crush the resistors, and pig tail from the top. Its pretty tight where they are so 1st do no harm.

anyway I am giving it back to him for a long term burn in, if goes well he will get the cabinet repainted and some new grill cloth installed (he has the right stuff). Should be nice when all done, I just figured it should be watched for a month or two before getting the nice paint job on it. That way I will not have to worry about it if something goes wrong in the short term. Of course with all those old resistor still in it I suppose it will need service at some time in the forseeable future.

[DaveWM]

Just for fun I hooked up my VCR out to a pair of rabbit ears, and used the predicta antenna to pick up the signal, all of about 4 ft away. Broadcasting "Planet of Vampires" from the mid 60's.

What a total deja vu exp, I am watching a poor B&W pic, just the way I would hav seen an old sci fi off a UHF indepedant station back in the 60's snow and all, its GREAT!!!

[DaveWM]

2nd one now, this one is mine, I have had it for over a year but never touched it due to the horror stories of working on a Predicta (this is the 17" princess model, red with metal frong grill).

Started by removing the main chassis (left the tuner in place for now). Very easy well thought out engeerning to get it out.

It not that bad at all, infact the compact sturdy chassis make it easy to flop over on the bench to get at the pcb (well the parts that are exposed anyway).

cleaned it with a soft brush and compressed air. Then moved on to alchol and q tips on the pcb to get the schmutz off the top of the pcb (I like to see what I am working on).

Popped off the IF strip cover, same deal Air, brush, q tip.

Stuffed the smaller can cap, it was complety open, was a bypass cap (low volt hi cap) for the vert amp, and a couple screen bypass caps in there.

I like the fact that there are no resistors tied to the can lugs just wires (this is the case on all 3 cans). Much easier to remove wire with out other stuff in the way.

Check the single doubler, fine, checed one section of the remaining 3 section cap, it check fine, I have found that if one section is good the remaining ofter are as well. I will get around to checking later.

Next up I start replacing all the black beauties, the 1st 4 all tested bad, I stopped checking after that.

There were a few that were standing up, I was able to use radials on those for a neater apperance.

I was able to replace about 70% of the caps from under the board, solder wick is your friend her since the solder sucker cant always get in tight places.

I am assuming the pcb is not though plated on the holes so you hav to bend the leads down flush to the board when soldering (I did not notice this on the 1st one, but figued it out quickly, I had not worked on such a old pcb before).

On the ones that just had no access at all I clipped, cleaned, and pig tailed the replacement cap, careful to use hemostats as heat sinks and to make sure the wire remnant did not fall though.

there were a few resistors that were out of spec. same deal as with the caps was able to do some from below.

The biggest problem was a big 390 ohm resistor next to the HOT. It was reading 470 but had a 10% band on it so I went ahead and replace it with a sand resistor, it was tight and I had to work from above, but got it in.

there were a couple I did not have so will have to make a surplus store run today (or pick up at the hamfest tomorrow).

I check all the tube resistance reading, all good to go.

checked all the coils (tranny,fly,vert,audio) again good to go.

the 17" crt was very very weak (no emmisons at all)

put the CR70 sencore to work (rejuv and auto restore) worked like a charm, strong emmisons and good cut off, and surprize good life test!

lubed the trim pots (little rusty and stuck) they seem fine now, beside I have some spare JIC.

cleaned and lubed the other pots (they were kinda funky on the resistance checks, seem ok now)

I am going to sharpen up my pick and tighten up some of the tube sockets that seem a bit loose, then will clean sockets, check tubes, clean pins.

I am thinking of making up a replacement for the fusistor (its there and good).

the replacement will be a couple thermistors in series and a fast blow fuse. That should soft the start to the caps and tube on the B+ and provide a sensitive fuse (with the soft start I will be conservative with the fuse rating).

Will also put a thermistor on the primary side to take some load off the switch.

Lastly will finsh up with a replacement saftey cap (the orig was a BB and was gone but the remaings where in there).

[DaveWM]

one thing is for sure, yes the chassis make it hard to work on, but the upside is its very stiff (box section chassis) which would translate to no flex at all on the pcb. From what I have seen this model anyway is pretty well designed and amazing how much TV was squeezed into a small space.

I really like how easy it was to get out of the cabinet the plug in tuner power supply was a nice touch.

[Charlie]

How was the area around the audio output tube? The pcb on mine was an issue there due to the heat of the 6BQ5. I was kinda surprised they used that tube with a relatively small speaker. Had to get creative making some connections there. That area of the board was a bit tricky being right next to the chassis. the only way to do it right is to remove the board... and I simply did not want to go that route.

[DaveWM]

not bad at all Charle, the tube socket is a bit loose but the pick should fix that. Maybe I have a low time one. I also thought the 6bq5 was overkill a
6AQ5 would have been plenty.

[DaveWM]

while checking over my work I noticed a couple caps that I "could" do from the bottom, so will re do those, and in what must have been a late nite frenzy I put a 500v cap in a 600v spot, I have the right one so will redo that.

I don't really mind as doing this is fun anyway. Something about getting it as "right" as possilbe is intriging as opposed to getting it close enough to work. I find that the solder wick and pencil iron can get into some pretty tight places. Looks like maybe only one of the caps will end up being totally inaccessable from the bottom.

I realy hope those k networks are going to be ok.

My buddy is really getting a kick out of his, I am glad I was able to help him out, its nice to see others get excited about old TV's.

[Charlie]

I built one of those combination components from scratch... turned out pretty good being my first time. Cant say it was pretty... next time i will use a small pcb... but still worked great.

[DaveWM]

yep thats the plan if need be. I have pleny of copper clad perf board, cut grooves in it for paths and solde as need be. did the one you replace have any obvious visual defect's (broken cracked etc...).

[Charlie]

No visual defects. I was advised by an uncle that i might as well do it while I had the set apart.

[DaveWM]

this one is in pretty good shape overall, it looks like it had a tube socked replaced (the sync tube socked) at some time, but other than that looks completly orignal. I amost hated to recap it, but its better that it works than be orig and set on the shelf never getting turned on.

[DaveWM]

pic of the now cleaned up pcb. lots of cleaner and Q tips.

Cap count about 13 so far, that .15 100v is next as is the .22 standing up.

there is a missing cap next to the vert out tube (c14 on the pcb but that is not what its called out as on sams) I could not locate on at the surplus store, its a .0015 1kv, in the plate circuit of the vert osc. I am going to a hamfest tomorrow, so hope to stock up on some caps there. If Not mouser will be next.

I have a .0022 orange drop 1600v and a .001 1kv but since its in the vert feed back circuit I would like to get close, I assume its somewhat critical for the correct frequency of the osc (although there is prob enough adj in the vert hold to get it close to the sync pulse).

I did go back and redo some of those over the top connections to below the board. I ended up with just 2 caps that I could not get. I replaced a few resistors, also under the board but for the big sand resistor (you can just see the white by the 6dq6 base).

I started off with a pcb that you could not see any of the print on the top, every spot you touched the q tip to came back filthy. After a couple hours work you have to try to find a spot that is not clean. Its nice being able to read the descriptions on the board.

did the socked tightening and cleaned the pins sockets with contact cleaaner.

I am hoping the networks are ok, if not I will be building replacements that are form and fit compatible using small copper clad perfboards and discreet parts.

Still need to do some tube testing mainly looking for shorts.

The fly looks pretty simple, I have a few small flys that I may play with to see if I can find one that at least matches the coil resistance. I wonder if anyone has tried to find a non listed sub?

[zenith2134]

single ended 6bq5? Fun, fun. Bet it has a great sound to it .

[DaveWM]

yep kind of a waste considering the speaker and enclouser.

Not being able to leave well enoung alone, I revisited one of he top mounted caps. I was able to bend my soldering gun (not my tool of choice for pcb work mind you) tip and get to the hard spot. little bit of solder wick to get all the solder out and some careful extraction yielded positive results. I now am down to two caps that vert osc plate and a single .22 upright cat bypass.

the vert osc should be no problem getting access to the bottom not easy but no harder than that last one. the upright one I may have to yell uncle on it.

Of course I could leave it for now. It tested fine with no leakage at all, even at 150v vs the 100v rating. Its a cathode bypass so I dont think it sees much in the way of voltage anyway. Of course if it did short it could possibly damage my vert out tranny so maybe a good idea to replace anyway.

Getting close to intial power up...

[andy]

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