horizontal width questions

sfluter

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I've read as many posts here as I could on the topic, googled it, read the articles at Bob Roberts, but still have a couple of questions, especially about the width coil.

How do you tell if they are bad or good? I have tried 2 on my k7000 chassis and neither makes any difference when I adjust it. I started with the core more or less even with the top of the coil and worked it back and forth, no difference, not even slightly. Beyond the sleeve, the coil and the core is there any other component to them? Both are intact and installed correctly. Is it normal to be able to remove the core completely, or is that an indicator it is broken? Is there a set range?

I read the Bob Roberts articles on coils and horizontal width. Pretty good stuff. The next place to look would be C38, but again I tried 2 different caps (same value, factory, does that make a difference?) with no luck on the adjustment. It worked before the trouble I got into recently, so is there another trouble spot in the horizontal section I need to look for or is it a matter of following the schematics back to the problem?

I honestly read and searched as much as I could before I posted this, but could not find much info on the coil itself beyond how to adjust it.

I am SO close to getting this chassis up and running. This is the last hurdle. BTW, the picture is too wide and I can't get it to shrink.
 
The width coil will only make slight adjustments. Sometimes you can adjust it as much as half-inch, but not always. and you have to turn it quite a bit to get that much movement.

As for changing C38, if you want to change the width, then you need to change the value of C38. Replacing it with the same value will give you the same picture. A larger value will give you a smaller picture, and a lesser value will give you a bigger picture...
 
Okay, I guess its time to order in some new PP caps for C38 and start playing. Thanks.
 
Width Caps

Bob Roberts sells a kit of diff caps in a Width cap Kit if you are like me and have a hard time getting an assortment local. I had width and stretch problems and ended up doing a complete reflow on the PCB to correct them. Good luck with that.
 
Okay, I guess its time to order in some new PP caps for C38 and start playing. Thanks.

If you have other parts chassis' lying around, you could pull one from there. Whenever I grab TV's for tube swaps, I usually pull any of these big caps of the proper range from the chassis (along with some other parts) to keep on hand when i need them.

Plus, you can always put two in series to get a smaller value/bigger picture:

V=cap value

(V*V)/(V+V) = new value

So, if the value now is 534 (.530uF), your new value would be .265uf (264)...
 
Its a .39 uF (K7000), and sadly the only parts chassis I have kicking around is another K7000, so it has the same value cap. I am going to order in a few different ranges from Digikey; .1, .22, .33 and .47. One of the first obstacles I am finding in this hobby is having some parts on hand. This chassis repair is taking so long because as soon as I complete one stage I need to order parts to finish the next!

BUT, I do have old TV's in the garage so maybe there will be something in there I can use. If not, its only a couple of days to get the replacements in.

Is there a voltage that should be present at the coil? I guess what I am asking here is could my problems be caused by something outside of the cap and coil. I am assuming because I have a stable horizontal picture the voltage is probably good. I just find it fishy identical coils and caps net the same result.
 
Is there a voltage that should be present at the coil? I guess what I am asking here is could my problems be caused by something outside of the cap and coil. I am assuming because I have a stable horizontal picture the voltage is probably good. I just find it fishy identical coils and caps net the same result.

Voltage, yes.

The picture size is first determined by the game pcb, and processed by the chassis. Swapping in different boards can give you a different size picture on a good monitor. I often run into this with my bench monitor when bench-testing boards. I'll hook up a Rastan, then adjust the position and size to get a good pic, then change to a Galaga and have to do it all over again....
 
Well I did manage to find a .33 uF cap, but it didn't make more than a slight difference in the width. The coil still isn't moving it one way or the other. Perhaps a slight improvement is all I am going to get, and if so I can live with it for now. I have another chassis coming in (tested) that I can compare values against. Having one good one around should be big help in getting the rest of them going. I'll play more with it when I get more caps in.

Okay, one last newb question and then I'll be on my way. Is there a thread/guide on bench testing chassis's? If I have it isolated, does it need to be grounded or does it just need the a/c like when its mounted on the frame.

Thanks for the help. If it wasn't for you guys pitching in with your advice there would be lot more dead machines for sale on Craigslist.
 
Some chassis won't fire up if it's not connected to the yoke. Some will. If you have one that will, then you have to worry about the anode firing and sparking or shocking you. If you have one like that, you can stick it the anode cup into a glass jar to keep it isolated.

i try to have a tube on the bench to connect it to while testing. I may power it up off the tube while testing/repairing, but I'll always put it on the tube once I start getting readings I expect to see on the bench. Once someone is well-versed with what to expect, even working on a chassis that requires a yoke (but doesn't have one hooked up) can be done if you know what voltages to expect without the load attached...
 
I just wanted to post a resolution to this issue.

It turns out there was nothing wrong with C38 or the width coil, the problem was the machine I was running it on. The monitor is installed in a Neo Geo Big Red 4 slot, running a 100-in-1 cartridge. I noticed my friends Neo Geo 100-in-1 looked exactly like mine, the width of the screen nowhere near to fitting.

When I tried the monitor in another cabinet it was fine. So I guess I'll tuck this experience in the old memory bank if I ever run into this problem again. Thanks again Modessitt. When you posted about different pcb's displaying different sized pictures it got me to look in a completely different direction than simply a problem with the board.
 
You can still use it with the 100-in-1 if you change that cap value. Now, if you plan to swap lots of different boards into this cab, you may not want to do this, but if you plan to leave it the same game all the time, go ahead...
 
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