My Attempt at Predicta Restoration - Page 4 - Videokarma.org TV - Video

DaveWM · #46 05-06-2010, 07:25 AM

it looks like the lin pot was taken out of circuit and replaced with a fixed resistor (the big sand resistor). This would be confirmed by no change in resistance from pin 9 to ground when adjusting the Lin pot (not the big round one it sould be a little trim pot marked lin adj). So you would be stuck with what ever the lineaity is (no way to adj) which may be ok.

the big round pot looks like a height adj. you should see a 275 marked pin on the side of the board, I think I can make that out. But to be sure you can check the output from the filter choke, that is also 275v. see if the resistance is 0 at that 275 pin when comparing to the output side of the choke, then you know its the right one.

The 275v source is used in several of the pin resistance measurements (as well as ground of course).

again you dont want to make a lot of changes until after a base line run, I just ran into that when working on a color set. was working with a bit of snow, I pulled the chassis, cleaned the tuner, then checked tubes, replaced a couple out of spec parts and end up with no snow, but sync and color problems. turned out to be some of the new tubes as I put the old ones back in and problems went away. My hickok tube tester showed the old tubes as weak and the nos tubes as much better.

I would try to limit myself to just replacing the papers, and bad eletros, do a base line run to see where you are, then make one fix at a time.

Resistance and voltage measurements can be helpful but do not aways tell the whole problem.

PredictaNoob · #47 05-06-2010, 04:57 PM

OK, so I'll let this thread rest a bit while I work the board loose from the chassis and start swapping caps, electros and resistors, and nailing down cold solder joints. Its going to take me a bit since we've got some events coming up. I'll try to pop up a picture or two when I make some progress.

PredictaNoob · #48 05-07-2010, 03:53 AM

I did want to report that I have definately decided to pull the main board. I replaced 4 caps last night in and around the audio section, since they appeared to be 'low hanging fruit". But even these fairly accessible caps weren't "a snap".
I won't actually pull the board, just "loosen it up", meaning I'll free it from the grounding stakes, but leave the wires connected. I calculate that I'll be able to lift the board about 5-6 inches away from the chassis. That should allow me easier access to most everything.

BTW, I finally found some solder braid at a different hardware store yesterday, yippee! They even had the HCL I was needing to etch some PCBs I'm building, and the water-soluble temporary spray adhesive for neat decal -pressure transfer system I'm putting together (for the control text on the back of this cabinet, as well as a good looking substitution for the silk-screened, reverse painted dial scale which is broken from my 1936 Blaupunkt KW741!)

On a related topic, I see that the previous repairman did not concern himself with lead dress. The Philco Service Manual dedicated an entire page to lead dress, so I suppose it is important enough to follow thier recommendations. I'll re-do the ones that are suspect.

I do see why people recommend NOT choosing a Predicta for you first tv restoration. I am having a blast though, and suprising enough, my wife remains positive about the whole project.
So, for today: Life, 'tis good!

DaveWM · #49 05-07-2010, 07:03 AM

the key is not to rush it, hopefully you will only have to fix the predicta once, and I can tell you have the right attitude for it. I used to just enjoy getting a couple caps done. Its a big difference when you are in it for fun vs. profit.

PredictaNoob · #50 05-10-2010, 03:41 AM

I wasn't able to devote much time this weekend to the chassis, although I spent a little time on the grille and cabinet (just to get it out of the living room!). I stripped the cabinet down to bare metal using paint remover and a wire brush wheel on my drill. There was a bit more rust that I realized, so I dabbed on some rust remover, then more wire brush action. The grille came out pretty good, using the blue/silver/black metalized cloth (for some Fender amp) I bought from Mojo. Since I had the original cloth to use as a guide, cutting the replacement was simple.
Before:

After:

I still have to clean up the corners...
I used fabric from a white linen napkin to cover the speaker hole prior to mounting the grill cloth and painted the masonite board a matte finish white. This made the hole invisible and the white brings out the silver threads very well.

DaveWM · #51 05-10-2010, 07:20 AM

Looking good

pallophotophone · #52 05-10-2010, 11:46 AM

One thing I noticed the first time I ever worked on a Predicta- all the point to point wiring is light gauge single strand wire which will break at the solder joint if it's moved too often. And who knows how much manipulation it had before you touched it ?

Pallophotophone

PredictaNoob · #53 05-11-2010, 05:22 AM

Quote:

Originally Posted by pallophotophone

One thing I noticed the first time I ever worked on a Predicta- all the point to point wiring is light gauge single strand wire which will break at the solder joint if it's moved too often. And who knows how much manipulation it had before you touched it ?

Pallophotophone

Thank you for the tip. Just to get an idea, I tested one suspicious looking lead, and you are right on the money. It snapped right at the insulation after only two bends. I think I will go ahead a redo all of the 'iffy' ones, snipping the wire, and stripping out some 'fresh' wire for the lead dress.

PredictaNoob · #54 05-11-2010, 05:34 AM

Last night, I freed all of the grounding points that hold the main board in place, and after removing the pots and freeing the V.O.T. from its mounting position, I was able to lift the board up plenty high enough to get to everything underneath with ease. I also was able to burn the snot out of my right hand ring finger with the soldering iron.
Its not a good idea for me to try left-handed soldering, I found out.

So replacing the remaining caps has become quite easy. Hopefully the resistors will arrive today or the next. We're gone for a week starting this weekend, so I'd like to make some headway before then.

Also, I am now a huge fan of Novus plastic polish (3,2 and 1). I was amazed at how many scratches on the CRT cover I was able to 'erase' using this system. I assume the 'smokey' tinting in the CRT cover is intentional, No?

And I tested a spot on the receiver frame using Simichrome paste. Wow, shined up in nothing flat. I'll finish up these cosmetics after I complete the board, or when I just need a break. I also find it simple to do these polishing tasks while watching a movie...

Patiently waiting for my "new" CRT tester and "new" pattern generator to arrive. And when I say patiently, I mean cussing the USPS and pacing a lot.

PredictaNoob · #55 05-11-2010, 05:02 PM

Not much time tonight, only replaced 5 caps and drew up my plans for decapitating the multi-stage electro can for re-stuffing. The wife just informed me that we'll be finishing her 'project' of cleaning out the basement tomorrow evening, so I don't expect much progress tomorrow either...

Also realized that Mouser short-changed me on a .047mF 400v and a .22mF 400v. Fortunately, I had both of those in stock already.

PredictaNoob · #56 05-12-2010, 06:05 PM

Finished off the last of the filter caps tonight, and will try to squeeze in some e-cap stuffing before we take off for a week. Tonight I also ordered a complete set of the J (or sometimes referred to a "K") networks from that guy at wadicta TV. A bit pricey, but I rahter pay for some good NOS ones than monkey around building replacements. I'll save that kind of work for when now replacements are available.

And Pallophotophone you were right, since I freed up the board and was wiggling it around so much, I managed to snap 3 different wires off. The connections were quite fragile, so I am glad they broke at this stage. They are secure now.

PredictaNoob · #57 05-14-2010, 01:27 AM

Since E3 is such a slender multi-stage, I decided to see what mounting the replacements directly to the MB would look like. They are in place. I hate it.
So, I am looking for alternative solutions/locations. (still no resistors yet)

Also, my "new" BK 465 arrived yesterday. With schoolboy haste I tore it out of the box, ran up stairs, gave it the once-over, looked up the settings for a 17DAP4, connected the appropriate adapter and fired it up. It powered on, allowed me to set the heater voltage, but nothing else registered. So, I calmed down, disconnected everything and gave it a closer inspection. While it appeared almost new, I now saw that the main connector had a chunk missing and that the red wire that should be connected to pin 1 was snipped away close to the outer insulation jacket. One small piece of solid core wire, a little heat shrink and solder, and the 465 was back in business.

Now that everthing was working correctly, I ran through the tests. No shorts, but low emissions. OK, so I give the rejuve feature a try. A *POP* sound that nearly made me piss my pants. I'm thinking, "OH NO!", What the...?" But, all is well as the tube now reads very good in the emissions test. PHEW! It showed on the low side of the cutoff voltage, but within the listed parameters (28v)

So, now I think it will sit and wait for the resistors to arrive. We are off this weekend to watch the Passion Play in Oberammergau.

leadlike · #58 05-14-2010, 04:32 AM

Your board looks good. On mine, I pulled the whole thing, replaced every single cap and resistor (which is excessive, I know) hooked it all back up, and powered it up. The set ran like new!

I probably would not have rejuvinated that tube-I typically set the heater voltage a little higher, about 8 volts, and then let the tester cook away at the tube for a few hours. The emission almost always goes up. Rejuvination is very hard on crts (on all but the most expensive testers, it is usually just a fat cap discharging itself into the crt gun) and in some cases will totally trash a perfectly fine crt.

DaveWM · #59 05-14-2010, 06:37 AM

I restuffed my slender Ecap, just like to keep the lead dress as orig as possible.

PredictaNoob · #60 05-14-2010, 07:14 AM

Quote:

Originally Posted by leadlike

Your board looks good. On mine, I pulled the whole thing, replaced every single cap and resistor (which is excessive, I know) hooked it all back up, and powered it up. The set ran like new!

I probably would not have rejuvinated that tube-I typically set the heater voltage a little higher, about 8 volts, and then let the tester cook away at the tube for a few hours. The emission almost always goes up. Rejuvination is very hard on crts (on all but the most expensive testers, it is usually just a fat cap discharging itself into the crt gun) and in some cases will totally trash a perfectly fine crt.

I guess I should count myself as fortunate. I won't be so hasty in the future. That "pop" made me come to my senses, and I won't soon forget it.