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HDMI to Old CRT
PL1:
To be clear, are 5v and the 75 Ohm resistor both connected to the wiper or is 5v not connected to the wiper?
Scott
Zebidee:
--- Quote from: PL1 on November 26, 2023, 02:20:20 am ---To be clear, are 5v and the 75 Ohm resistor both connected to the wiper or is 5v not connected to the wiper?
Scott
--- End quote ---
Scott...
What are you asking exactly? You should not connecting 5v + 75R -> GND to same pin.
There are three pins, so I'm suggesting:
1) 5v input
2) GND + resistor
3) blanking output -> jungle
As usual for pots: three pins, three separate connections.
EDIT: which means like the third schematic pic you showed Scott.
After a sleep, I realise that I didn't erase the "U-turn arrow" pot symbol on the right side - I was treating that as just a pot symbol, rather than an actual connection, but now I get that it was confusing you to thinking the 5v was meant to be attached to both the input and wiper pins (though that seems crazy). So like this:
I don't think it really matters which way around the blanking and GND pins are, or what numbers you assign to which pin. So long as they are connected as described. I'm also not sure exactly how abstract3000's pot is physically wired WRT the "wiper" as the pics don't show that. The only pic he provided of the actual circuit board is from top and very low-res.
PL1: which pin do you call the "wiper"? The middle one? Does it matter (the pot works the same, just the high/low is swapped)? I don't know which pins are physically connected, but the pencil schematic only shows two pins connected.
So, with only two pins connected, the pot is just acting as a variable in-series resistor, rather than a voltage divider. I guess the pot would vary the blanking voltage a little, but not very much (and not very high). Further, the original schematic showing 75R resistor at the pot's blanking output would pull the voltage very low anyway.
So instead, attach the 75R "termination" resistor to the pot's GND pin (the one not currently connected). You don't need signal "termination" on this blanking anyway, it isn't even a video signal as such. Furthermore, I also think that re-assigning the resistor to the pot's GND connection is a good idea to protect somebody from completely shorting the PSU's 5v rail to GND through the pot. If anything, maybe a higher value resistor (say 1K) could be considered.
PL1:
--- Quote from: Zebidee on November 26, 2023, 06:32:40 am ---After a sleep, I realise that I didn't erase the "U-turn arrow" pot symbol on the right side - I was treating that as just a pot symbol, rather than an actual connection, but now I get that it was confusing you to thinking the 5v was meant to be attached to both the input and wiper pins (though that seems crazy).
--- End quote ---
I figured that the "crazy" connection of 5v to both the center pin and outer pin wasn't right, but you might have intended to use the pot as a variable resistor with 5v connected to the center pin and the 75 Ohm resistor providing a minimum resistance between 5v and ground. Variable resistor + resistor = a fake pot with a non-zero minimum resistance -- the technique the KADE guys used for Atari 2600 paddles on miniConsole+.
--- Quote from: Zebidee on November 26, 2023, 06:32:40 am ---I don't think it really matters which way around the blanking and GND pins are, or what numbers you assign to which pin. So long as they are connected as described. I'm also not sure exactly how abstract3000's pot is physically wired WRT the "wiper" as the pics don't show that. The only pic he provided of the actual circuit board is from top and very low-res.
PL1: which pin do you call the "wiper"? The middle one? Does it matter (the pot works the same, just the high/low is swapped)? I don't know which pins are physically connected, but the pencil schematic only shows two pins connected.
--- End quote ---
Wiper is always the center (#2) pin. On a schematic, this connection point is indicated by the arrow. As you mention, the connections to the outer pins (#1 and #3) on a pot can be swapped and it just reverses the direction you turn the knob to increase/decrease the voltage/resistance at the wiper. Swapping connections to pins 1 and 3 does not change the resistance or voltage drop of the resistive element between them, it just changes the wiper voltage when the contact is at the blue line from 4.5v (5v on pin 1, ground on pin 3) to 0.5v. (ground on pin 1, 5v on pin 3)
The wiki has a more detailed theory of operation and this exploded view for anyone wanting to learn more about how pots work.
http://wiki.arcadecontrols.com/index.php/Analog_Encoders#How_a_potentiometer_provides_the_voltage_for_an_analog_encoder_to_measure
Scott
abstract3000:
Thanks for the Feedback, much appreciated.
--- Quote from: Zebidee on November 26, 2023, 06:32:40 am --- The only pic he provided of the actual circuit board is from top and very low-res.
--- End quote ---
I apologize for that, and @Scott I really couldn't tell you the correct way the Schematic is supposed to look but I got some Hi-Res photos and have described where everything is going so hopefully that will clear up the confusion :)
So This is the Top side, I know it's painfully obvious what I marked but just indicating what I was looking at. And the orientation of the Trim Pot
So here is the Explanation I should say for lack of better words.
(whoops I messed up, I fixed the image after closer inspection)
The Red Circles indicate the Pins on the Trim Pot
Left pin Went to the 75Ohm Resistor (Now removed) Then to Ground
Center Pin connected to Right Pin
The Right Pin Goes to a Diode, then Back to the TV Motherboard I assume to Blanking.
Here is a Closeup of the Diode
In other news I went through and tried every setting in the service menu, managed to fix the Vertical Overscan, but nothing with RGB Cuttoffs or any other setting made any sort of noticeable difference besides "tone" which did what it sounds like yet not a solution. I just saw The previous posts, but didn't get a chance to read closely through them as I wanted to get you guys the Exact information of what was happening. I will look over those now.
@Zebidee, I like your solution for adjusting the voltage, those pots you used could you provide me a link to the specific ones that would be needed on Mouser or DigiKey? and those solderless connectors I really like, what are they called for searching purposes?
Zebidee:
--- Quote from: PL1 on November 26, 2023, 04:09:28 pm ---I figured that the "crazy" connection of 5v to both the center pin and outer pin wasn't right, but you might have intended to use the pot as a variable resistor with 5v connected to the center pin and the 75 Ohm resistor providing a minimum resistance between 5v and ground. Variable resistor + resistor = a fake pot with a non-zero minimum resistance -- the technique the KADE guys used for Atari 2600 paddles on miniConsole+.
--- End quote ---
Yeah, but no. There are many variants, but I'm just suggesting to make a simple voltage divider with the pot.
Putting a resistor on the GND pin, as a minimum load, is sensible. Not trying to be fancy here.
PL1: If you put a resistor between the wiper and the GND you change the behaviour of the pot (in terms of voltage response) to approximate a log curve (or is it anti-log? always confusing), rather than linear. This might well be appropriate and feel "natural" for the Atari 2600 paddles, but beyond the scope of what I'm talking about for this mod.
It just so happens that I covered this in depth (with pics, graphs & even a re-usable spreadsheet), a few months ago, on another post about decent volume controls:
http://forum.arcadecontrols.com/index.php/topic,167662.msg1765413.html#msg1765413
--- Quote ---The wiki has a more detailed theory of operation and this exploded view for anyone wanting to learn more about how pots work.
http://wiki.arcadecontrols.com/index.php/Analog_Encoders#How_a_potentiometer_provides_the_voltage_for_an_analog_encoder_to_measure
Scott
--- End quote ---
Thanks for that link, it is a great resource. :cheers:
PS: I had just written all this then saw a new post from abstract3000, so will just submit this then read.