Yet another Predicta Holiday restoration

[Notimetolooz]

Originally Posted by Down Under

Nice work, Bob.

It's always interesting to see you think up new ways of doing things. Did you rebuild the couplates because they were faulty or because you will be far more confident with the restoration? Surface mount components is a good idea... how do you fit these? Machine, tweezers or just great eyesight and care?

When I work with surface mount parts I use tweezers and a lighted circline magnifier similar to these.
http://www.dazor.com/illuminated-magnifier-lamp.html

That works for me as long as the resisters and capacitors are no smaller than 0603 size. For TV work you would want to use the larger sizes anyway because of power levels.

[Geist]

Hi All;
If you look at Bob's previous Predicta Video's.. He has many previous network, how to do video's and the steps for doing them.. As well as improvements on the process..
THANK YOU Marty

[bandersen]

Yes, except that I made these using a different technique. Before I used perf board - this time I tacked them together in free space.

Originally Posted by Down Under

Nice work, Bob.

It's always interesting to see you think up new ways of doing things. Did you rebuild the couplates because they were faulty or because you will be far more confident with the restoration? Surface mount components is a good idea... how do you fit these? Machine, tweezers or just great eyesight and care?

I've worked with small parts for years and my eyes are still god enough so I found this fairly easy.

The couplates that look like a bunch of vertical tubes are really made up of carbon comp and ceramic caps. I've measured a bunch and the resistors are have typically drifted high.

The flat, thin couplates like at the top of my photo are made using material deposited on a ceramic substrate and measure more closely to the specs. So I suggest leaving those alone unless you know for sure they're bad.

As for SMD, I've seen various techniques used. The most basic is to dispense the solder paste with a syringe, place components with tweezers and "bake" the board to melt the solder paste.

More recently, I've seen board vendors supply a laser cut sheet metal mask so you can squeegee all the solder paste on at once. Like silk screening.

[Notimetolooz]

Originally Posted by bandersen

Yes, except that I made these using a different technique. Before I used perf board - this time I tacked them together in free space.



I've worked with small parts for years and my eyes are still god enough so I found this fairly easy.

The couplates that look like a bunch of vertical tubes are really made up of carbon comp and ceramic caps. I've measured a bunch and the resistors are have typically drifted high.

The flat, thin couplates like at the top of my photo are made using material deposited on a ceramic substrate and measure more closely to the specs. So I suggest leaving those alone unless you know for sure they're bad.

As for SMD, I've seen various techniques used. The most basic is to dispense the solder paste with a syringe, place components with tweezers and "bake" the board to melt the solder paste.

More recently, I've seen board vendors supply a laser cut sheet metal mask so you can squeegee all the solder paste on at once. Like silk screening.

Yes, typically when boards are manufactured they use the silk screening technique and solder all the parts at once. You can do it by hand one at a time by placing a small blob of solder on one pad first, then re-melt the solder while placing the part. After that you solder down the other terminal(s).

[bandersen]

You can do the silk screening technique by hand too. Here's a good tutorial: http://youtu.be/qyDRHI4YeMI

[bandersen]

My parts arrived and I finished with the main board and modules.


I also cleaned up the icky, sticky wires with denatured alcohol


Next up, under the chassis...

[bonanzaman]

Hey, Bob.....I really like the new k-net treatment ....looks to be much easier than the perfboard assembly, and once they are glued up and painted, should be fine....after all, we are not spliting the atom here, are we! Thanks for allowing us to check out your work!

[bandersen]

The board has been re-installed without incident


I also figured out these loose wires went to the now missing AC switch. I'm going to just short them together until a replacement arrives.

[DaveWM]

I got a princess chassis on the way, was planning to have it as a backup, but I think I may do the full restoration treatment ala Bob. Since its not for a current working set I figure I do not have a lot to lose, this way I can just swap a chassis out if need be.

Nice work as always Bob

[bandersen]

Thanks and I'll be doing a Princess soon too. It's the first vintage set I ever tried to restore a few years back but stopped when I realized I needed more experience on easier sets first.

BTW I saw your posts in the ARF classifieds - glad you got that straightened out.

[DaveWM]

Originally Posted by bandersen

Thanks and I'll be doing a Princess soon too. It's the first vintage set I ever tried to restore a few years back but stopped when I realized I needed more experience on easier sets first.

BTW I saw your posts in the ARF classifieds - glad you got that straightened out.

yea man I could not believe I pulled such a bone head move to send the money to some random Ebay. I was really glad I got it back so quickly.

[bandersen]

I replaced the filament dropper with three Dale power resistors. The thermistor was replaced with a couple Ametherm 220 ohm in series to simulate the 400 ohm original.


I stuck a 15 ohm resistor in the CRT socket to simulate it's filament.
Success

[Down Under]

Thanks again for this very useful info, Bob.

You're wetting my appetite, I can't wait to start mine! Luckily I have sourced all the needed cosmetic parts to finish the 17 inchers. Now I'm just waiting on the players to do their bit. One question remains: to powdercoat or not to powdercoat... I'm not sure how I'll reestablish the lettering on the top of the cabinet where it says Brightness etc...

Cheers and well done,

Adam.

[bandersen]

I finished with replacing the paper caps and resistors under the chassis. All the electrolytics too, but some are temporarily tacked in. I'll do a more permanent job once the set is working.



I'll be powering it up without the CRT using a power resistor in place of the filament.

Hmm, only 75 volts at the output of the filter choke. Should be around 300.


Eventually, I traced the problem down to the voltage doubler diodes. My DMM's diode check function showed them as good, but a 0.1 volt forward drop didn't seem right.

Sure enough, when I tacked in a couple temporary 1N4007, B+ came right up to where it should be, I got sound out of the and hear a high pitch from the horizontal circuit.


Finally, I popped the CRT off a restored Holiday set and got a raster


Even better, I can tune in a station although the vertical is messed up.


After adjust the vertical linearity and maxing out the height, I'm almost able to fill the screen. Also the vertical hold is very touchy.

[bandersen]

The replacement control arrived and it tested good so I installed it. Power. volume and contrast are all working correctly now


I then went through the vertical circuit and everything checks out. For example, here's the vertical sync pulse at 2 V p-p just as indicated. So although it's a little touchy, I think it's working as designed.


I'm going to let it run for a while then ship it back to it's owner. I sure hope he's able to wire it up to his CRT and get it running at his end.