RCA TV - Help needed with overscan correction

I've got an RCA F27689, built in 2001. Not the world's best 27" TV, but decent enough for me right now.

I'm a bit of a tweaker, so I've already found out how to get into the service mode of my TV. I'm also a fairly cautious type, so I also wrote down all the default values for my set before attempting to mess with anything. I've also read some horror stories that suggest if you're going to be fiddling with things in the service menu, you'd best be prepared for the consequences of messing something up permanently (or at least enough to require a visit to a service technician). You may consider me a fool, but the potential benefits of tweaking make that a risk I'm willing to take.

Using a Digital Video Essentials test pattern as a guide, I can see that some parameters make visible changes: I've found vertical position, vertical size, and horizontal position, for example.

However, the one thing I really want to change -- horizontal size, to correct for what I feel is an awful lot of horizontal overscan -- has thus far eluded me. I'm beginning to think maybe it can't be adjusted at all (!), but I don't really want to believe that just yet. I'm hoping maybe there's another password to set, and further parameters to adjust. Or that one of the parameters I don't see doing anything can be made to do something, somehow. I don't know -- I'm grasping at theoretical straws here.

Could somebody with a little (or a lot) more experience than I've got give me a couple of pointers? Thanks kindly...

[crossposted to sci.electronics.repair and rec.video]
Reply to
Karyudo
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Quick update: the chassis number is CTC197A8.

[crossposted to sci.electronics.repair and rec.video]
Reply to
Karyudo

I don't know your set in detail, but I have some suggestions.

I would think it would be a good idea for you to invest in the service manual. They should give instructions for the complete set-up of your set. There will be test equipment necessary to do all of the set-ups to any great detail. What you want to do, is mainly visually referenced, using a test pattern on the screen.

In some models of sets, they use some resistors with jumpers that are soldered to them to set the width. Some sets have a connector that is selectable for the width. Another way of doing this, is that there may be a pot or width coil on the main chassis in the horizontal output area.

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JANA
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Reply to
JANA

If it needs to be adjusted you will need Chipper Checker and if its really got overscan then the set needs to be repaired.

Reply to
kip

Kip, why do you need the Chipper Check to make adjustments on this set?

I don't recall any horizontal size adjustment on the 197 chassis. This is not uncommon on 27" televisions.

Leonard

Reply to
Leonard Caillouet

I don't have the exact CTC197A8 scematic, but other 27" CTC197 use parameter 5 as horiz size adjustment in the service menu.

Reply to
RonKZ650

This is correct. The set does have horizontal size adjustment, parameter 5.

Leonard

Reply to
Leonard Caillouet

Yes But did the set develop a fault that now gives excessive scan or not, or does he want to reduce what is normal on those TV,s. Has the TV always been like it ??? Gotta tell us more info.

kip

Reply to
kip

I've done a bit more searching, based on the fact that I now know the chassis number can also tell me a lot!

I've found the complete set of service codes for the CTC197:

Parameter # Description:

0 Security Pass 1 Error code 2 Error code 3 Error code 4 Horiz Phase 5 EW DC (Horiz size) 6 Pin Cush Amplitude 7 Pincush Tilt 8 Pin Top Corner Correction 9 Pin Bottom Corner Correction 10 Vert Centering 11 Vert Size 12 Vert Countdown Mode 13 Red Bias 14 Green Bias 15 Blue Bias 16 Red Drive 17 Green Drive 18 Blue Drive 19 Gemstar OSD Horizontal 20 Gemstar OSD Vertical 21 Gemstar Horiz. PIP 22 Gemstar Vert. PIP 23 Gemstar PIP Window Vertical

...and sure enough, this matches what I've been able to figure out on my own thus far.

However, I also found a forum conversation that goes thusly:

Q: "I've located the proper parameter in service mode to adjust the horizontal width of my RCA TV, however, it doesn't affect the display when altered. The vertical sizing and centering parameters do work. I was using P5 which was indicated in the Service Manual for a CTC197 chassis. Any thoughts?"

A: "Your set may not have the option to adjust the pin or horizontal size depending on the size of the TV and feature level it was built with. I can guarantee that if it is smaller than a 27" it does not have any horizontal adjustments available."

Sadly, this also matches what I've been able to figure out. So I guess if the horizontal size can be changed, it won't be through the service menu. Damn.

Yeah, it's always been like that, and no, there's no fault per se. But I still feel that there's too much stuff being cut off. Titles on some movies or TV shows, for example, are butted right up against the edge of the screen -- and sometimes they're even cut off a bit. So I'm guessing I'm missing part of the 'TV title safe' area?

I can change the horizontal position adjustment (P:04) from one extreme to another, and still not see the very edge of the picture on either side. I mean, this is *acceptable*, but it's not *optimal*. It's disappointing to learn that this is likely not an easy tweak to make. But I'm a persistent geek if nothing else, so I'd still be interested to hear what I might have to do "under the hood" to have a shot at reducing the overscan on my set.

Any further ideas?? (Thanks, everyone!)

Reply to
Karyudo

Sounds good. Where can I find one? I've heard something like Thomson something-or-other, but that's not quite enough detail. Any more hints?

All three of these are strategies I would pursue. Changing out a jumper -- or even a resistor -- is within my cautious capabilities, I think. If I were to take the back of the set off, what would I be looking for, and where would I look for it? Any hints on what sort of label (e.g. printed on the PCB?) I'd see? (Oh, and don't worry: I'm not going to touch anything metal until it's been off for the better part of a day, lest I fry myself or something else).

Thanks for your help!

Reply to
Karyudo

Reply to
kip

Do not try to alter the horizontal width in hardware. You obviously do not understand the operation or design of the circuits enough to do so without a high probability of damage to the set.

Le>

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Reply to
Leonard Caillouet

You misunderestimate me. *Of course* I don't understand the circuits enough -- yet. I'm not going to do a damn thing until I do, and until there's a much lower probability of damage to the set (preferably hovering around 'nil').

What I really need now is not dire warnings, but more information about either the circuits themselves, or where to find the information. I know service manuals exist; I'd like to know how to get one. I'm educated, bright (enough), and cautious. I'm not going to mess anything up, because I won't touch anything until I'm pretty positive I'm touching the right thing.

One observation: TVs suck. Computer monitors (and I mean *all of them*) have allowed the end user to adjust just about every damn thing

-- including horizontal width, of course -- for at least about a dozen years. This is not rocket science, it's just crappy engineering. The fact that I've even got to consider some dangerous hardware mod just to get the whole picture on the screen is ludicrous.

Reply to
Karyudo

There might be an off-value or mislabelled part in the deflection circuitry. If there is a non-polar electro in the deflection circuitry this may be the culprit affecting the width.

Another thing that may affect width is the high voltage being too low. Recall that as the electron acceleration in the crt is increased the beam becomes stiffer and requires more magnetism to deflect. This was a classic case of a bad crt in the old days since as the beam got weaker the width would increase. It would even follow the scene brightness changes. I guess with better supply regulation this effect is rarely seen in modern sets.

Well, if all else fails you might try robbing some power from the horizontal deflection coil by adding a parallel load to it. Perhaps an experimentally selected flame-proof resistor in series with a NP cap? This is only a suggestion and not a known fix.

M*i*k*e

... If all else fails, hurl it across the room a few times!

Reply to
Asimov

How much overscan are you talking about? The set is designed with between 5 & 10 percent, and closer to 10 is not uncommon.

You can get the manuals from Thomson Consumer Electronics or their distributors, such as Tritronics. Be sure to get the training manuals as well as the service manual.

Leonard

without a

Reply to
Leonard Caillouet

I'm not exactly sure how much it is. Yet. I have yet to put up the DVE screen that shows how much overscan I've got. I'd guess I'm at the high end of normal. It's not *terrible*, but I think it could be a fair bit better. I'm sure overscan hides a multitude of evils, but I'd like to see for myself. I want to be more hands-on than RCA's letting me be...

Thanks, Leonard!

Reply to
Karyudo

Dude, if I had money enough to go out and buy a new TV, I probably would. Actually, no, I wouldn't: I have a TV that works just fine. I just want it to work a little *better* than 'fine'. Part of the fun is to figure out what to tweak and how to tweak it.

And if I did decide to buy a new TV, I doubt I'd start with Apex, even though I'm in that minority that has had excellent results and a long

-- continuing -- life out of his AD-600A.

What's so hot about the Apex TVs, may I ask?

Reply to
Karyudo

What is wrong with the guy wanting to tweak on his set?

Leonard

Reply to
Leonard Caillouet

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