K7500 width transistor

Here is the screen with the screen pot at its lowest
 

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there's also the Sub Contrast. I never mess with it, should probably just center it
Is that on the break out board? If so it's already centered and the brightness pot is maxed out

Edit could new pots kill the transistors on the neck board? Also could I use the transistors from a K7900?

Ediit 2 ested neckboard transistors and they are good, not sure what else could cause a loss of color and brightness/contrast
 
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Is that on the break out board? If so it's already centered and the brightness pot is maxed out

Edit could new pots kill the transistors on the neck board? Also could I use the transistors from a K7900?

Ediit 2 ested neckboard transistors and they are good, not sure what else could cause a loss of color and brightness/contrast

Sub contrast is on the deflection board (main chassis) by the remote board header. VR800. You can see it in the manual


1747273368671.png

Someone has already mentioned that R811 may be bad. Have you checked that? It should be 75K ohms. Test it out of circuit.

Common failure points on these is U500 (LM1203N) color amp on the neck board. All you can do is swap it out and see. If you have another working U2000, K7400, K7500, or U5000 monitor, you can try swapping neck boards to help troubleshoot.

The new pots won't kill a transistor unless you used the wrong values, and even then I doubt it would.

You should not substitute a K7000 chroma transistor for a K7500.

There is a troubleshooting guide for this you should look at for more help https://www.wellsgardner.com/wp-content/uploads/2016/08/K7400_25_inch-1.pdf


1747273292211.png
 
Sub contrast is on the deflection board (main chassis) by the remote board header. VR800. You can see it in the manual


View attachment 819506

Someone has already mentioned that R811 may be bad. Have you checked that? It should be 75K ohms. Test it out of circuit.

Common failure points on these is U500 (LM1203N) color amp on the neck board. All you can do is swap it out and see. If you have another working U2000, K7400, K7500, or U5000 monitor, you can try swapping neck boards to help troubleshoot.

The new pots won't kill a transistor unless you used the wrong values, and even then I doubt it would.

You should not substitute a K7000 chroma transistor for a K7500.

There is a troubleshooting guide for this you should look at for more help https://www.wellsgardner.com/wp-content/uploads/2016/08/K7400_25_inch-1.pdf


View attachment 819505
I was watching a zenomorp video and he had a neckboard where like the cluster of resistors by where the ribbon cable plugs in were bad. real obscure failure, but it'll strangle the color signal coming in and will result in bad color output.
 
Sub contrast is on the deflection board (main chassis) by the remote board header. VR800. You can see it in the manual


View attachment 819506

Someone has already mentioned that R811 may be bad. Have you checked that? It should be 75K ohms. Test it out of circuit.

Common failure points on these is U500 (LM1203N) color amp on the neck board. All you can do is swap it out and see. If you have another working U2000, K7400, K7500, or U5000 monitor, you can try swapping neck boards to help troubleshoot.

The new pots won't kill a transistor unless you used the wrong values, and even then I doubt it would.

You should not substitute a K7000 chroma transistor for a K7500.

There is a troubleshooting guide for this you should look at for more help https://www.wellsgardner.com/wp-content/uploads/2016/08/K7400_25_inch-1.pdf


View attachment 819505
R811 is good so that's not it, and I didn't say k7000 I said k7900, I do not have another chassis, this monitor didn't even have one when I got it, so I bought one untested and recapped it
 
I was watching a zenomorp video and he had a neckboard where like the cluster of resistors by where the ribbon cable plugs in were bad. real obscure failure, but it'll strangle the color signal coming in and will result in bad color output.
This I will check when I get home
 
is C519 on the neckboard supposed to be populated? on mine there iis nothing there but there is remnants of legs of something soldered in there

EDIT nvm just saw in another thread that it was cut from factory
 
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Put the old pots back on and kinda have color back but still having issues
 

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Put the old pots back on and kinda have color back but still having issues
define issues. you don't know how to white balance? flip TPG to where you have a mostly black screen. the cluster of 3 cutoff pots on the neckboard, turn them up one at a time until the black background turns to the color you're turning up. then turn it back down to where it's black again. before you do that, get brightness where it needs to be. turn the brightness pot on the remote board up until you get grey dots in the black. if you can't get it with the brightness pot, then turn screen up on the flyback, then back the brightness pot off until it's black.

your colors look muddy, it's probably the tube. see if you can get them to pop more with the contrast pot.
 
define issues. you don't know how to white balance? flip TPG to where you have a mostly black screen. the cluster of 3 cutoff pots on the neckboard, turn them up one at a time until the black background turns to the color you're turning up. then turn it back down to where it's black again. before you do that, get brightness where it needs to be. turn the brightness pot on the remote board up until you get grey dots in the black. if you can't get it with the brightness pot, then turn screen up on the flyback, then back the brightness pot off until it's black.

your colors look muddy, it's probably the tube. see if you can get them to pop more with the contrast pot.
i have been messing with the pots and they are not really doing anything
 
Last update for now until I can get a vga cable and hook a pi up to it, this is the best I can do and I am pretty sure that dark blue at the end is supposed to be black, the reason it's like that is because I have the screen pot turned up and the brightness pot maxed out other wise it is way to dark

EDIT R310 is supposed to be 1.2ohm 5% 2W resistor, it is reading as 7.2 ohm, this might be my issue
 

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R811 is good so that's not it, and I didn't say k7000 I said k7900, I do not have another chassis, this monitor didn't even have one when I got it, so I bought one untested and recapped it
K7900 = K7000
 
so something odd happened, I turned it on and right as I was about to start tweaking the pots the whole picture jumped to a really good brightness, would this be a fly back issue or the lm1203 chip?

Also what is the temp of the lm1203 supposed to be? Mine gets about 50c or more I can't remember
 

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K7900 = K7000
what's more infuriating is I know people that think K7500 = K7000 because they share a K and a 7.

so something odd happened, I turned it on and right as I was about to start tweaking the pots the whole picture jumped to a really good brightness, would this be a fly back issue or the lm1203 chip?

Also what is the temp of the lm1203 supposed to be? Mine gets about 50c or more I can't remember
your issue is in the neckboard. the flyback doesn't have anything to do with electron gun emissions, it just illuminates the face of the tube. it's why people that jack the brightness up to compensate for poor electron gun emissions don't achieve what they think they're trying to do. I would venture LM1203 reaching 50 C is not correct but be mindful those things run very hot. you can help the cause by spacing the large resistors on the bottom out. (I don't have time to find a visual aid in my vast repository now)
 
what's more infuriating is I know people that think K7500 = K7000 because they share a K and a 7.


your issue is in the neckboard. the flyback doesn't have anything to do with electron gun emissions, it just illuminates the face of the tube. it's why people that jack the brightness up to compensate for poor electron gun emissions don't achieve what they think they're trying to do. I would venture LM1203 reaching 50 C is not correct but be mindful those things run very hot. you can help the cause by spacing the large resistors on the bottom out. (I don't have time to find a visual aid in my vast repository now)
I know which resistors you're talking about and I have already done that, I also put the lm1203 in a socket and I guess I will order a replacement and see if that does anything
 
Okay I am now back to this with some updates

First update is I built a mount for the chassis with a piece of wood from lowes and some screws and nuts I had here at home and it works and looks good

Second update my replacement lm1203n came in the mail and the screen is still imo not bright enough but I am starting to think it might be my eyes

Waiting for something to arrive from Amazon to connect my raspberry pi to the monitor and play a game to see how it looks,

I have also noticed the drive pots are very twitchy and I am starting to wonder if that might part of the issue

I did replace all three color pots and those are working better now imo

But any ideas are welcome
 

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just play your games

you also don't adjust monitors to TPG, you adjust them to the game you're going to be running
 
just play your games

you also don't adjust monitors to TPG, you adjust them to the game you're going to be running
Well then I will leave that up to whoever buys it, as I am fixing this thing to sell
 
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