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Author Topic: External V-Size Pot  (Read 515 times)

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porkins

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External V-Size Pot
« on: September 04, 2018, 11:18:35 am »
I want to install an external V-Size pot adjustment to my cab. I would like to do so without having to remove or alter the existing pot. I am hoping it would work to have an external pot that connects to the existing pot in parallel to allow me to make tweaks. Would this work? Any suggestions on type of pot to use? And how would I wire in the new pot? I am thinking I would wire it same-to-same. So + to +, Grnd to Grnd, and Signal to Signal.

It is a Wells Gardner K7000 series. It appears that the V-Size pot is 200 Ohms. I will have to check the range of resistances I want to get with my multimeter, but I think adding a 500 Ohm pot would give me the ranges I need?

lilshawn

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Re: External V-Size Pot
« Reply #1 on: September 04, 2018, 12:58:23 pm »
I think the better question is why do you need to keep messing with it? you should be able to set it and forget it. set the Vertical size to fill the screen.

that said, pots have a limited amount of time you can move them before they start to drift out of spec. (usually in the 100's of cycles)

porkins

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Re: External V-Size Pot
« Reply #2 on: September 04, 2018, 01:15:02 pm »
Running Mame with custom resolutions. I have it trimmed right now so most vertical games fit nicely, but then I have some black space at the top and bottom of most horizontal games. And there are some other vertical games (PacMan, Galaga) that are even large, so the scores for those get cut off. Would be nice to be able to adjust the V-Size on the fly.

dmckean

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Re: External V-Size Pot
« Reply #3 on: September 04, 2018, 10:55:14 pm »
porkins,

The way most people deal with this would be to open pac-man and adjust the monitor so it just barely fits and they call it done.

porkins

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Re: External V-Size Pot
« Reply #4 on: September 05, 2018, 10:08:09 am »
Agreed. I might try that and see how I adjust myself to the other games. I am also thinking I will just use the MAME sliders to adjust PacMan and squish it a tad. I think I can deal with that. :)

markc74

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Re: External V-Size Pot
« Reply #5 on: September 05, 2018, 03:13:44 pm »
If you're tv has a 4:3 and 16:9 mode you may be able to tweak the geometry on the 16:9 so that you can fit 256 lines. That's what I did on my Blip cabinet. You can then either use the remote to switch modes, or if you have a scart connection, wire up a switch to do it.

I have 4:3 set as 224 lines and 16:9 as 256 lines and that covers the classics at least.

Paradroid

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Re: External V-Size Pot
« Reply #6 on: September 05, 2018, 05:26:31 pm »
I have 4:3 set as 224 lines and 16:9 as 256 lines and that covers the classics at least.

That's a smart approach. Nice!

This might be of interest.

Recently I retro-fitted an RGB modified TV into a cab and installed a recessed pot for V-size behind the marquee. Works a treat!

Don't let lishawn's talk of pots going out of spec scare you: you're going to be eyeballing the screen every time you resize so you're not relying on the pot reproducing the exact same resistance for a particular rotation point. Besides, most pots don't have a narrow tolerance to start with (except extremely expensive industrial options).

You're not going to be able to wire the pot in parallel without creating headaches for yourself. Better to use a 2PDT switch if you want to be able to switch between to settings.
My MAME/SCART/CRT blog: SCART Hunter

lilshawn

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Re: External V-Size Pot
« Reply #7 on: September 05, 2018, 10:02:28 pm »
Better to use a 2PDT switch if you want to be able to switch between to settings.

the horror.

kinda bad for the deflection circuit when it gets left to spool wide open for that split second when the contacts disconnect but before they connect again.

dmckean

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Re: External V-Size Pot
« Reply #8 on: September 05, 2018, 10:48:25 pm »
Agreed. I might try that and see how I adjust myself to the other games. I am also thinking I will just use the MAME sliders to adjust PacMan and squish it a tad. I think I can deal with that. :)

There's always going to be some compromise when trying to run every game ever made on one horizontal monitor. None of the art on vertical games ends up looking right anyway because the scanlines are running the wrong direction.

Paradroid

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Re: External V-Size Pot
« Reply #9 on: September 05, 2018, 10:57:16 pm »
kinda bad for the deflection circuit when it gets left to spool wide open for that split second when the contacts disconnect but before they connect again.

Agree. Should have stated "...that can be switched when the monitor is off".
My MAME/SCART/CRT blog: SCART Hunter

buttersoft

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Re: External V-Size Pot
« Reply #10 on: September 06, 2018, 08:21:31 pm »
None of the art on vertical games ends up looking right anyway because the scanlines are running the wrong direction.

An excellent point.

  
 

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