Predicta Princess - a few questions.

[maxhifi]

I got a red princess about a year ago, and made a thread about it here. I then put it away and stored it. I have been reading the sams manual, watching youtube videos, and am getting more and more ready to dig into it. I have a few questions though.

1. Replace capacitors more or less can be taken for granted. But how about resistors? Is it necessary? I see some do it, some don't. I figure if I am removing them to check value may as well just replace, but I don't want to totally remove the originality of the set.

2. Rebuild all PEC modules? Looks like a ton of work, but then again who wants to do this twice.

3. IF alignment necessary? I have a B&K sweep/marker generator and can probably do this, but I lack experience.

4. Tube sockets get a bad rep. I remember reading about surplus sales of Nebraska having them? Is this true? Maybe I should get some on hand before restore begins?

5. C53, in the yoke.. 120mmf, 5kV.. leave it or change it?

[Gregb]

I am on my third one right now. Yes, replace all caps, I test the old ones to see what kind of shape they are in and on this set everyone has been bad so far.
I checked all and replaced about 60% of the resistors in this set and about the same in the last two.
The only modules I have replaced are ones that look like they have had some work like resistors bypassing sections and such. I also replaced the one feeding the vertical output tube, sorry I forget which K number it is.
I have not had any socket issues so far but others have so keep an eye out.
So far the only thing I have had to do for alignment is the audio section to make it clear and quiet.

Gregb

[maxhifi]

Hi Greg,

Thanks for the advice! I will order a full set of resistors, 60% is pretty bad! I took Apart the TV today. The CRT tested bad at first but became good after giving it 3 minutes at 3.7V, and then turning back down to 2.68. The chassis is really dirty, the circuit board is covered in a greasy film, and there are many brands of tubes, only a few are philco.

[Jon F]

On mine, I replaced the Vertical Feedback and Horizontal Multi networks in addition to all paper/electro caps. Also, almost half of the tubes tested weak/bad.

I didn't replace any resistors on mine, except for the fusible resistor. I tested some and they were OK, and the set plays well with good geometry and stability so I figured I'd leave it.

I sprayed down my chassis with water to clean all the crud off it, and let it dry overnight over a heat vent. Not really sure if it is good practice though so tread at your own risk.

[Gregb]

My Princess was really dirty as well, I used Spray Nine and q-tips as I was changing components, I have attached an after picture. Make sure you draw yourself a real good diagram before disconnecting all the wires to the board.

Gregb

[maxhifi]

Man my board is a long way from yours! I am thinkong of getting white heat shrink and numbering all the wires before I remove them, but the lead dress is going to be a challenge to get right, it's a real rats nest!

[Gregb]

My board looked like yours before I started! I just made a drawing of the board showing all of the pins and what wires were attached, it was easier than I thought it would be. Worked on the first try!

Gregb

[kvflyer]

Originally Posted by Gregb

My Princess was really dirty as well, I used Spray Nine and q-tips as I was changing components, I have attached an after picture. Make sure you draw yourself a real good diagram before disconnecting all the wires to the board.

Gregb

Nice job on that PCB! On a side note, the series string sets have tubes that are extremely inexpensive. I bought several for my set even though I have not had time to work on it. There is a tube vendor in Orlando, FL who often has many of the tubes on sale for $1.00 each. The other ones for the most part are only $3.00 each and all are NOS, various brands. Tubes in my Predicta also tested very weak for the most part.

[maxhifi]

I think only someone who has done this can appreciate how much of a feeling of accomplishment I have for liberating this circuit board!

[maxhifi]

I cleaned things up a bit, using many many Q tips, and then de-soldered all the paper capacitors, and checked their value against the schematic. Phil Nelson's website is extremely valuable (yet again)!

One question I have is about R43 and C34A. They look to have never been installed on my circuit board. The components were absent, and it looked like the board was soldered without them (holes filled with solder, and look identical to other original solder). What do you guys think, should I add them? There's no notes on the Philco schematic or in Sams about them being optional.

Note: I see the same components are absent on Greg's board too.

[Eric H]

It's common for boards to have holes for components that weren't used in every model, I wouldn't add them.

[Gregb]

My set seems to work fine without them I would leave them out.

Gregb

[maxhifi]

Okay cool I will leave them out.

[Don Lindsly]

Those components were deleted "to improve sound sensitivity and facilitate production" per Philco engineering change bulletin.

[DaveWM]

something you may want to check, the plate load resistor on the sync separator. Cant really test it in circuit as it is in series with some resistors in one of the networks.

In circuit IIRC it was 25k, but that was with the board all hooked up.


I have had a couple predictas now that had very soft sync, both time it was that resistor open or very high.

You can of course find this as well with simple voltage checks but since you have already pulled the chassis, you may as well replace that one since its covered by the shield. That is assuming there was a sync issue.