Need help with a diagnosis

[Keebo]

I recently picked up a near mint Defender for a mere $200, what a steal. For the first month it ran flawlessly except for  occationally the fire button wouldn't fire. Now my monitor will not display, I can hear the game running I just can't see anything on the monitor. When I start it up there is a flash of white like the monitor is coming on then it just goes black. When I turn it off there is a circle on the monitor that appears for a split second displaying mutiple colors, just like the old televisions. I checked all of the fuses, thay are fine, and I do get neck glow after its been turned on for about 30 seconds. I'm thinking it has to be one of three things, either Caps, flyback, or it needs a new chasis. I haven't taken it out yet but from what I can see the caps look fine but looks can be deceiving. I'd appreciate any insight into this matter that I can get.  

WG K4600

[Rickn]

Not sure how much help this will be..... but that circle with multiple colors is what is called "afterglow or spot killer". What the monitor expects is that when powered down the high voltage will slowly drop allowing all beam current to disapate.
In this case something is shutting it down prematurely.
This could be a high voltage shut down issue due to a problem with the high voltage?
try disconnecting the signal of the game from the monitor and then powering up just the monitor. If you have constant orange glow from the heater, then increase the setting on the G2/screen (bottom control of the flyback).
If the CRT lights up (slightly gray) at least we know the cRT is fine and will need to move on with other possibilities?

Good Luck
Rick

[Keebo]

try disconnecting the signal of the game from the monitor and then powering up just the monitor. If you have constant orange glow from the heater, then increase the setting on the G2/screen (bottom control of the flyback).
If the CRT lights up (slightly gray) at least we know the cRT is fine and will need to move on with other possibilities?

Ok, I disconnected the signal from the game to the monitor. I turned the power on and after about 3 minutes I could see a glow on the neck. I began to adjust the only knob on the flyback. It was already turned all the way to the right, I'm guessing that was up. So I adjusted it down slowly and back up and the screen stayed completely black. Im guessing this means that the problem is within the monitor.

Any other suggestions?

[Keebo]

I've been doing some hard digging into the bowels of the forums and here is what I have found.
A cap kit would do my monitor some good but it more than likely will not fix a black screen, from what I've discovered about cap kits they fix monitors that are displaying funky things. Since mine does not display at all except for at power on and power off. Next, it seems that there is no recollection of a fly back going bad on the WG 4600.
The only other thing that I have found that could be the problem is the black level trim pot on the Video Interface Board. Now the post I read called it a black level trim pot so I'm guessing since there is nothing labeled Black, which it's the actual black knob that is labeled 'screen'. The post said that the carbon gets a hairline crack in it. I'm posting a picture for verification. Are these easily attainable and swapped out? Does it seem like I'm on the right track?

[qrz]

schematic:  http://technical-department.servegame.com/monitor_schematic_diagrams/wg_k4600.jpg

check C605,C501,C503,C625,C201,C619
R418,R419,R624,R641,R642,R423

[Keebo]

One thing that I just noticed, the neck glow on my WG4600 is very dim compaired to the neck glow on my Disco chassis. Could a bad tube be causing all of this?

[qrz]

filament voltage is scan derived and your B+ voltage is low. hence dim fils...

[Keebo]

filament voltage is scan derived and your B+ voltage is low. hence dim fils...

Sorry, I'm a noob at all of this but I'm trying to learn. That said, I have no idea what you just said.

If it's dim what can be done?

[qrz]

>> check and/or replace the previously mentioned parts .....

capacitors are a storage device ( albeit small ) .
when the value changes, or ESR rises it will likely be a problem ( depending on cap type and circuit tolerances ).
resistance changes can be a factor .
and lastly , semiconductors with leakage / shorts/ opens , etc...

btw, a scan derived power supply means the seconday voltages are produced by the flyback rather than the incoming voltage.
therefore, the fact that you HAVE lit filaments indicate the Houtput stage is functioning .
being dim indicates the voltage from the regulator circuit is probably low.  primary voltage will influence scondary voltage .

for illustrative purposes such as :

1:1 turn ratio is an isolation xformer   output voltage will be close to that of the input .
1:10 is a step up xformer  secondary voltage will be higher and current will be lower.
10:1 is a step down xformer  ( typical "wall wart " )  secondary voltage will be lower and current will be higher

actual turn ratios vary per xfomer type/function

sorry u asked ?

[Keebo]

I'm not sorry at all, I love to learn.

[qrz]

     now, about those parts ............?