K4600 Brightness Issues

FrizzleFried

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My Pacman's monitor was starting to show signs I needed to rebuild... and I remembered that I had bought a "working/rebuilt" K4600 a couple years back still sitting in a box. I pulled the old and dropped in the new expecting it to work... and...

Well... here I am. :(

The new chassis is exhibiting an odd behavior. It will increase in brightness until a certain point... then cut brightness to a very dim level, then increase in brightness to a certain point... then cut brightness...etc...etc...etc...

Using the screen pot on the neckboard does nothing immediate/noticeable, but it does seem to effect the level of which the monitor cuts brightness to and the level it takes it to on the high end before cutting out.

I figured perhaps the blacklevel pot was going bad on the one daughter card... so I tried the daughter card from the chassis I pulled... unfortunately it exhibits the very same behavior.

I have not tried exchanging the horizontal/vertical daughter card as of yet.

I've also noticed at the very high end when the screen is very high it affects the focus as well...

Aside from this issue, the monitor looks beautiful.

Any suggestions on where to look?

Thanks!
 
Funny, I've got a 4600 in my Joust that is doing the exact same thing. I just keep adjusting the brightness down on the flyback but then I come back and it's too bright again. I figured it was the flyback going bad but haven't looked into it more.
 
This was SUPPOSED to be a working/recapped/rebuilt chassis...

>sigh<

:)

Oh well. I would really prefer to figure out what the problem is with this chassis vs trying to rebuild the original... I destroyed the original's width coil taking it off the frame.
 
I now know who sold it to me too. :D

But I can't give the guy any hell. I bought it 12/2010... it sat in a box for 2+ years.
 
Funny, I've got a 4600 in my Joust that is doing the exact same thing. I just keep adjusting the brightness down on the flyback but then I come back and it's too bright again. I figured it was the flyback going bad but haven't looked into it more.

The 4600 does not have a brightness adjustment on the flyback. That pot on the flyback is for adjusting the focus only.

The "SCREEN" control is on the neckboard and is usually set around the ten o'clock position. Mounted directly behind the screen control is resistor R419 which is a 330K, half watt resistor which can go bad affecting brightness. You need to unsolder one lead of this resistor to test it or you'll get false readings. Over the years, I've found a dozen of these resistors that failed.

The "BLACK LEVEL CONTROL" on the video interface board is the main brightness control for this monitor. It is a high failure item. it develops a hairline crack inside it in it's carbon resistance element which can cause either fluctuating brightness, no brightness, or full brightness symptoms. The solder joints on the male header pins on the main board where this board plugs in often go bad and require resoldering. The bad solder joints on this connector will cause fluctuating brightness too.

In all cases, I must assume you have already installed a full capkit and replaced the black level control pot. Bob Roberts and Zanen Electronics include the black level pot in their capkits.
 
Thanks Ken,

I will check out that resister and the solder joints. The BL pot is new.
 
Tube is fine. The monitor was working as normal aside from some geometry issues.... pulled the old chassis and dropped in the new and this is what I am getting.

:D
 
Oops, I guess mine must be a K4900. I could have sworn it was a K4600 but I've only been reaching in to adjust the brightness knob on the flyback. I'll take another look. Sorry for the bad info.



The 4600 does not have a brightness adjustment on the flyback. That pot on the flyback is for adjusting the focus only.

The "SCREEN" control is on the neckboard and is usually set around the ten o'clock position. Mounted directly behind the screen control is resistor R419 which is a 330K, half watt resistor which can go bad affecting brightness. You need to unsolder one lead of this resistor to test it or you'll get false readings. Over the years, I've found a dozen of these resistors that failed.

The "BLACK LEVEL CONTROL" on the video interface board is the main brightness control for this monitor. It is a high failure item. it develops a hairline crack inside it in it's carbon resistance element which can cause either fluctuating brightness, no brightness, or full brightness symptoms. The solder joints on the male header pins on the main board where this board plugs in often go bad and require resoldering. The bad solder joints on this connector will cause fluctuating brightness too.

In all cases, I must assume you have already installed a full capkit and replaced the black level control pot. Bob Roberts and Zanen Electronics include the black level pot in their capkits.
 
Welp, color me disappointed.

I replaced the resistor and re-flowed the headers... same issue.

This isn't something intermittent either.... it doesn't happen at different intervals... when it starts increasing brightness it does so until full bright then cuts off to low brightness... in a steady, predictable manor.

Also I note that when in "high bright" stage it will sometime cause severe focus issues... and when not in "high bright" stage the focus doesn't really focus... it actually increase intensity of the colors?!? but when in "high bright" stage and out of focus, the focus knob actually...focuses?!?

This is all very strange.

The screen knob still does very very little to nothing. I'm using two different black level cards... one of which I know is working... both produce the same issue.

Behavior appears to change as the monitor warms up... I thought I had it adjusted where it wasn't doing this... and it "kept" for a couple minutes... only to pop super bright again...
 
It almost appears like there is some "high intensity" protection that kicks on at a certain intensity level.... kicking it back a visual "octave" so to speak...

Very strange indeed...
 
Check the solder on the neckboard, particularly the tube socket.

I would also suggest testing the tube. It may have an intermittent short which could be blasted away with a rejuvenator.
 
If it's not the resistor Ken's talking about (and the one just behind THAT one, if you look at the schematics it does the same thing).... then I'd guess it's the flyback on the new chassis. Usually focus drifts when the brightness is turned up considerably... but since when it's dim, the focus knob doesn't work right, I think something's internally screwed up in that flyback.
 
Check the solder on the neckboard, particularly the tube socket.

I would also suggest testing the tube. It may have an intermittent short which could be blasted away with a rejuvenator.

Will check solder on the board. This tube was working fine with the prior chassis. The prior chassis just had some geometry and jailbar type issues. I pulled that chassis and dropped this chassis in. When the issue I am having appeared I pulled the black/level daughter board from the chassis that was running in the game prior and dropped it in the newly installed chassis and the problem remained thereby eliminating the black/level board.

I would imagine if it were the tube, it would have happened with the other chassis. At this point I think I am going to re-cap the 12 or so caps on the older chassis that was working... then drop in the nice clean daughterboards from the new chassis and hopefully call it a day.

:)
 
If it's not the resistor Ken's talking about (and the one just behind THAT one, if you look at the schematics it does the same thing).... then I'd guess it's the flyback on the new chassis. Usually focus drifts when the brightness is turned up considerably... but since when it's dim, the focus knob doesn't work right, I think something's internally screwed up in that flyback.

I can say for 100% sure that the focus knob actually increases and decreases brightness when I first fire up the monitor. About 10 minutes ago I fired up... the screen was black... I adjusted the focus knob and the damn thing lit up. I could then increase and decrease brightness with the focus knob.

:confused:
 
Lest anyone think I am nuts... here is a video. In this video I am adjusting the focus knob ... the only knob on the flyback...

 
Welp,

To conclude this saga... I re-capped the original main chassis. 11 caps total. Woo hoo. I then installed the newer cards and plugged it all back in.

Success. Picture looks great.

There is something wrong either with the main board of the newer board I have or the flyback.
 
had the person you got the "working" chassis from replaced the flyback? it almost looks like from you video they switched the focus wire with the screen wire...
 
It's been 2 years since I bought it. The seller doesn't remember... as I wouldn't expect him to after a couple years.

;)
 
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