Dove right in! Help with RCA 21-D-8628

[old_tv_nut]

Originally Posted by BandDirector

I keep forgetting the horizonalt/vertical deflection yoke, could that be the culprit? ...

No, that is not a yoke problem.

Edit: it looks like the vertical sweep frequency is way too low, about 1/2 the correct value of 60 Hz. There must be a component that's way off value/open or not connected properly.

I ordered 2 replacement vertical output tubes, still cannot get the center bar to sync, and the picture refresh is still too slow. Moved the electrolytics to safer spots and added in new solder/junction spots.

I tried to start testing using a signal gen, oscope, bias, etc.; no golddurn clue what I am doing!! And never have enough probes, or a diode tester, or proper attenuator pads, etc. I need to make some testing pads, get some raw coax, proper connection points, etc.

Is there a way to just 'reset' or reverse/speed up the refresh rate ? Is that what sweep means? There are some things I sort of understand, but no where near what I would prefer!!

[old_tv_nut]

Originally Posted by BandDirector

...

Is there a way to just 'reset' or reverse/speed up the refresh rate ? Is that what sweep means? There are some things I sort of understand, but no where near what I would prefer!!

Yes, picture "refresh" rate is the rate at which the beam sweeps vertically.

To repeat: sweep rate being off by a factor of two indicates that there is a bad/wrong value component or mis-wired component (or multiple) components. To find miswiring,
1) look at each point where multiple components connect and verify you have the same components and same number of components connected to that point that the schematic indicates.
2) look at each component and verify where each end is connected.

Patience is necessary!

I didn't realize how long it really takes to study a schematic. It has taken me weeks, with the chassis, to really start to follow the layout. It isn't easy when the components aren't appearing where you think they should be!

[Notimetolooz]

You might benefit from downloading "Television Simplified" by Kiver.

https://worldradiohistory.com/BOOKSH...r-5th-1955.pdf

Of course you still have to get good at reading schematics.

EDIT: While on the subject of this book, it was printed in 1955 so some things (like CRT deflection angles) changed through the years after that that.
I suggest you start with Chapter 1, The Television Field, then Chapter 9, CRTs, then 10, Power Supplies, then 12, Synchronizing, lastly Chapter 13, Deflection.

[Electronic M]

The vertical sweep frequency (refresh rate in modern computer monitor parlance) is set by the RC (resistor capacitor) time constants of components in the vertical circuit.

It does take time to read a schematic when you're new to it and PCBs often slow down the process as it's difficult to tell which component leads from parts on top are soldered to which points on the bottom...I tend to use a small flashlight to locate pads and or a DMM meter with a continuity beep mode to speed things up.

Did you read all the values off the original caps or did you recap off the schematic? Sometimes the schematic has the wrong value due to a typo....

About 12 years ago when I was in highschool my first TV restoration was a 1954 Zenith...it was full of bumbelbee capacitors and I didn't know how to read them when recapping the set...so I changed all the caps based off the values on the Sam's schematic. The video detector diode in mine was bad so I had no video to judge sweep performance....then I had to move from Florida to Wisconsin and things got put on hold and I no longer had a parts budget or the parts I removed from the set. I was able to fix my video detector and discovered my vertical had the opposite problem it's sweep frequency was twice what it should be so the image looked like you cut a slide in half, overlaid the two and projected it. At that point I traded the circuit found the resistors and caps were good according to the Sam's. Schematic, but that one vertical cap in the Sam's schematic was a factor of 10 different from the Sam's parts list....so Sam's had a typo. Without the original part to confirm and no cap supply or budget back then to try the other cap value I fixed it with what I had: a resistor decade box and a bag of scrounged resistors. I used the decade box to find a value that would work (trying it on different resistors in the circuit) then once it was right I added in a fixed resistor of the same value.

While the decade box method did work for me I wouldn't recommend it except as a very last resort.
If I wasn't flat broke back then I would have tried the other cap value first. Also it's safer to change capacitance than resistance since resistors can change tube bias and overload tubes causing premature failure of affected tubes.

Don't think of using the decade box till you have verified each resistor is in tolerance, each cap is the right value and everything is connected to the right points and tube subs have been tried...(also worth while to walk away from the project for a week or two, forget about it, and then check your work with fresh eyes...it's easy for a mistake to be staring you in the face and some mental block stops you from recognizing it (it happens to even the best of us).

Originally Posted by Notimetolooz

You might benefit from downloading "Television Simplified" by Kiver.

https://worldradiohistory.com/BOOKSH...r-5th-1955.pdf

Of course you still have to get good at reading schematics.

EDIT: While on the subject of this book, it was printed in 1955 so some things (like CRT deflection angles) changed through the years after that that.
I suggest you start with Chapter 1, The Television Field, then Chapter 9, CRTs, then 10, Power Supplies, then 12, Synchronizing, lastly Chapter 13, Deflection.

Downloaded it, this looks like a great read. Thank you!

I did replace using both the printed value on the paper caps, and using the RCA printed service manual schematic.

I do have chassis A (the original), and it does appear to have some newer caps on the vertical board, I may remove that PCB 500 and use it as a model to test all the component values that I am still troubleshooting.

Here is the 'original' (chassis A, that came with this television) PCB board for the vertical oscillator and sync output unit.

It appears that the caps have been updated from the older paper caps, chassis B (the one in the tv) had the older paper caps.

Assuming this television properly worked at one time, I have not removed any of the Rs and Cs from this board. I will match the components to their values in the RCA service manual scheme.

I've been practicing removing boards from my backup chassis. I have learned that I am NOT a fan of clipping and resoldering caps and resistors just to test them. If that isn't best practice, too bad; this project needs to wrap up. I have every confidence that what I am doing by checking each object is a much safer, time friendly (I'm an unemployed teacher with plenty of time!) and I feel that basic step by step is simply the way to go. It will make testing poorly functioning components much easier.

I have a full set of back-up wiring, a separate chassis, and a duplicate of all parts minus a functioning main transformer. This is what I have learned:

1) Slow down and triple and quadruple check each action
2) Study the schematic and check whether there is a misprint (thanks, gents)
3) Refer to the old (chassis A) boards, someone did a decent repair job replacing 90% of the paper capacitors
4) Don't be bothered by placing and testing this chassis (chassis B, the replacement bought from 'Sonny' aka Radiolaguy that happened to have this exact 'Norman' RCA 21-D-8628 model) back in the set.
5) Any issue is starting to make some sense with everyone's help! Not to mention that excellent book link posted above.

Voila!

Still needs some work. Horizontal sweep is a little edgy
Sound is funky

[old_tv_nut]

[Kevin Kuehn]

Originally Posted by BandDirector

Voila!

Still needs some work. Horizontal sweep is a little edgy
Sound is funky

Looking very good.

[Electronic M]

Nice work.

Her head does look a pinch stretched. It could probably benefit from tweaking the vertical pots and centering with a crosshatch test pattern or a circle that touches top and bottom, but the untrained eye isn't going to notice it as easily as many of us would.

[Kevin Kuehn]

Originally Posted by Electronic M

Nice work.

Her head does look a pinch stretched. It could probably benefit from tweaking the vertical pots and centering with a crosshatch test pattern or a circle that touches top and bottom, but the untrained eye isn't going to notice it as easily as many of us would.

Although the scan lines look quite uniform top to bottom.