Adding Vertical Linearity control...

[Apache Thunder]

Ok I recently acquired this CRT TV. It's a KV-1393R. The awesome thing about it is this happens to be the woodgrain version which wasn't something I expected. Found it on a local Facebook garage sale group for my town and the seller only had a photo of the front with the model number not in the shot. Was only $10 so figured it would be good to have just for the tube. Well as it turns out it does have the same tube that the KV13TR24. But convergence is a bit worse on it. The yoke has no adjustment rings on it (just has a plastic sleeve covering where they would go) But since it's a woodgrain model I swapped the tubes anyways as I want this TV as my main one now. The tube from this was put in the KV13TR24 where I decided to completely re-align the yoke to fix the shift in the red convergance (was shifted a bit to the left). Since there are no adjustment rings I guess the factory managed to get the tolerences good enough in the tube when they built it that the yoke they put on it didn't need them. So I took off the rubber wedges and redid the whole setup. Managed to get it as good as it will go, but red is still shifted up a bit near the center right of the screen. Can't really get it any better so won't work on that tube anymore.

But the good news is the tube from the KV13TR24 has nearly perfect convergance anyways with only slight issues in a couple corners. Most of which I ironed out with convergence strips. Anyways this tube seems to work great in this set. Photos:

https://i.imgur.com/VLYGAcS.jpg

https://i.imgur.com/u0VRMjx.jpg

I have decided I will try to RGB mod this TV instead of my KV13TR24. But like the TR24, this one also requires that I do it via the neckboard as the OSD muxes into the main jungle IC output via only the green channel. (An even more simplified circuit then the TR24. With that one they also connected the Red channel)


Now to the only issue I really have with the new TV I got. The vertical linearity is a bit off and the bottom of the screen is a bit more squeezed then the top. This is starting to bug me so I want to try and fix it. But unlike the TR24, there is no vertical linearity trim pot on the board. But the vertical deflection circuit looks really similar to the TR24 and the deflection yoke connector is identical to the TR24 (else I would have had to swap yokes which I didn't have to do at all here. Only the C2 wire pair coming off the neckboard had a different connector on this board and I was just able to reuse the original sine it's not part of the deflection yoke/can be seperated. Even the neckboard is the same with the same part number.

But yeah it's bumming me out that I can't fix the linearity on this set. It's not that bad. But it's noticable when there's any 16:9 content being used. (black bars look off center as a result) and any game with vertical scrolling like the Sonic games on my Genesis.

Here's a schematic to both the KV13TR24 and the KV-1393R:

KV1392R:
https://i.imgur.com/TCZGBrc.jpg

KV13TR24:
https://i.imgur.com/Ktmqfac.png

And a photo of where it is on the spare TR24 board I have: (long story on how I have a second main board to this TV. I have a different thread here specific on the KV13TR24, you can probably read up on that there if you want. )

https://i.imgur.com/aD5Wlsj.jpg

I can't seem to find RV504 (what it's marked as on the board) on the schematic so that should give you an idea of where it is in the circuit. It's not setup as a voltage divider it seems like just a basic resistor bridge of some kind.

The KV-1393R may have a fixed resistor for this instead of a variable one. I just need to spot where it is. If none is present I will have to insert one. I have a spare 18k varible resistor trim pot I can use to dial in what I want. I did this with the sharpness control on this TV.

The KV-1393R doesn't even have a customer serviceable sharpness control. Can't be adjusted via remote nor no control for it on the front of the TV. (OSD on this TV is very simple. Only really can show channel number/mute status/sleep status/video input and that's it. Picture controls are all analog controlled via control knobs)

The schematic though shows that the jungle IC does have a pin for sharpness control. But it's tied to a fixed resistor and a diode of some type going to ground. So I pulled the resistor (it turned out to be a 10k resistor which was 8k under what the schematic called for) and used my trim pot which was soldered to wires so it extends out and can be reached easily. I reduced it to about 5k and the sharpness is about the same as my KV13TR24 (increasing resistance value just made the picture softer, so decreasing it was the way to go). Happened to have a fixed resistor of that value from a board to a dead TV I no longer have so took the trim pot out and soldered that alternate resistor in. Worked like a charm.

Now I plan the same procedure for vertical linearity. But I need to find where I would need to tap into on the board. I think they used a fixed resistor. But perhaps someone more experience in reading schematics/TV circuit design can chime in and help guide me where I need to look.

Also I can't find the full service manual for the KV-1393R. I found a rather badly scanned PDF of the schematic. Had to stitch it to a single image myself as it was scanned in in parts on multiple pages.

I found one site that has it, but it's behind a pay wall. How annoying.

If you happen to have the PDF for this service manual let me know.

[MKL]

RV504 is in parallel with R545:



And clearly R545 is a fixed value resistor that replaces the variable resistor. Hence, if you put RV504 you remove R545.

[Apache Thunder]

Ahh I see so that's where V. Lin control would be on TR24. Now I need to know where the equilivent location would be for it on the KV1393R. Maybe R536? It's connected to ground from the Vertical input/output pins on the jungle IC (which interconnect to IC501). It's a 10k resistor while the fixed resistor value for V. Linearity on TR24 is 22k. Unless it's R507? That one is a 3.3K though.

[Apache Thunder]

Still looking to find the resistor that governs Vertical Linearity.

My best guess after comparing the schematics of both tvs is that maybe I need to adjust the value for R545 (schematic calls for 3.9k here. Capacitors in this part of the circuit are labeled the same on both boards, but this particular resistor has a pretty different value compared to the one on KV13TR24).

Another one I think may be the one if the above one isn't, is R507. It goes to ground and is tied to the same trace that goes into the Vertical Size trim pot (RV503) and it's value is 3.3k on the schematic. I measured the R545 resistor on my spare KV13TR24 board (where they used a fixed resistor and RV545 is not installed) and it is pretty close. Slightly above 4k. Though I was measuring it while in circuit. Though not sure if that matters or not. It doesn't match the value shown on the schematic...Which may be normal since the factory adjusted it to fit the tube they installed.

But at this point I'm still not sure. The way vertical size/centering is handled on these tvs are slightly different. Different enough that I need a second opinion on this. R545 on the KV1393R is similar. Close to C544 and C545 (these capacitors are identical on both TVs and appear to be wired in a similar manner)

[viletim]

Still looking to find the resistor that governs Vertical Linearity.

My best guess after comparing the schematics of both tvs is that maybe I need to adjust the value for R545 (schematic calls for 3.9k here. Capacitors in this part of the circuit are labeled the same on both boards, but this particular resistor has a pretty different value compared to the one on KV13TR24).

Resistor R541 (82 ohms) is for linearity.

For more info read this datasheet for the TDA1170 vertical IC. 'LINEARITY ADJUSTMENT' page 21 (second method).

[Apache Thunder]

Oh I see. It terminates to ground behind a capacitor just like the KV13TR24. Only there's an extra resistor after it unlike the TR24...Actually R543 is present on TR24 too in the same place it looks like. (has a slightly different value but the icon the schematic uses for it is the same)

Not sure how I missed that. Still new at reading schematics. It was organized a bit differently then the KV13TR24 so I wasn't sure.

I guess they decided to use R541 for a different purpose on the TR24. R545 is linearity on the TR24.

Thanks for pointing it out. I will put in a trim pot to find a new value. Once I see a good setting I will pull the trim pot out and get the ohm reading from my multimeter and install a matching resistor. Shouldn't be too difficult. I don't think I have to adjust it a whole bunch. Might even already have a resistor to match what the new reading will be.

[Apache Thunder]

Ok it was indeed the V Linearity control! Put in a 250 or so ohm varible resistor. Looks like reducing resistance helps fix linearity. If my math is right by measuring the free pin on the trim pot (to avoid doing an in circuit measurement which won't match what it is outside of circuit) that means I need a 33 ohm resistor in place of the 82 ohm resistor.

Here's how I came to that conclusion. 2 pins of the trim post are connected to where the old resistor use to be. Left pin on one side and the output pin on the other. The right pin is left unconnected. The right pin to middle pin ohm reading on the original 82 OHM spec was 150 ohms when I had left to middle pin ohm set to 82 OHMs. After adjusting it for the TV to fix the linearity, the ohm reading on the middle to right pin (the right pin not connected to anything so the trim pot being in circuit won't impact my measurements) rose to 199 ohms.

So I subtracted 150 from 199 to get a value of 49. Since the middle and right pin ohm reading increased that means the left to middle ohm reading decreased. So I subtrack 49 from 82. I get 33.

There happens to be some that match that exactly (on a 1% tolerance level anyways) on eBay so I'll order that part and install it when it arrives. For now I'll keep the trim pot installed.