WG 4900 Issue

gregr

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Wg 4900- fixed

I picked up a newer version of the 4900 not working, the thought was that it was a bad flyback, so I recpped and installed a new flyback. The picture attached is what I'm getting, and ideas where to start trouble shooting this issue.

Thanks
Greg
 

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So I did some research on how to test a transitor and this what I've learned and found testing the 2 tranistors at Q302 and Q303 (2SC2073).

Q302
BE: .56
BC: .56
EC: --

Q303
BE: .56
BC: .56
EC: .94

Based on what I read, EC to should not conduct, so should I assume that Q303 is bad.

I tested both of these while they were still in the board, do they need to be test out of the board.

Thanks
Greg
 
Bump for a little more help - I've checked all of the tranistors and traces across the 300 section(they all seem to test ok except Q302 which seems like it could be the issue), is it possible that a bad resistor could be causing this, do I need to check them as well and do all of them need to be tested out of circut.

What else should I be looking for - there is nothing obvious as I look at the board.

Thanks
Greg
 
The gameboard? That isn't a gameboard issue. If you mean the chassis, I'm not sure what that will tell you if you know the yoke is good. What you're seeing is a raster issue. It's either the yoke or the chassis.
 
I meant the chasis is being tested in another working 4900, so I know the yoke works fine, and I know the yoke and chasis are compatible.

Thanks
Greg
 
You know the yoke and chassis are compatible because:

A) They are both a 4900 chassis and a 4900 yoke?

or

B) Because you know you have a later series 4900 chassis matched to a later series 4900 yoke, or an early version 4900 chassis matched to an early version 4900 yoke - and not a mix of early and late versions.

Just checking. There are two versions of the chassis, and they use different versions of the yoke.



Otherwise. That entire vertical section need to be inspected, all the way top the yoke connector. Wiggle every large part and look for movement on the pads...
 
The chasis model number 2061433-040 is a newer version which matches yoke 2021111264, which is the yoke I'm using to test the chasis. Additionally, I have test 2 additional working chasis with this yoke with no problems.

If my information is correct the older version chasis model number is 2061433-023 which matches yokes 2021111194 and 2021111201.

With all of that being said, I'm sure it is the chasis that is the problem.

What I've done so far is to test the continuity from the yoke pins through the vertical section with no issues. As I mentioned before there is nothing obvious, so I was wondering if it could be one of the transistors or resistors that could be casusing the problem.

Any further help would be appreciated.

Thanks
Greg
 
4900 - fixed

After testing everyhthing - I determined that there were a few things that seemed out of range so I decided to replacement them all. I got my package from Bob Roberts at 4:30 and less than 2 hours later I have a working 4900.

I replaced Q302, Q303, Q352 and IC 501.

It really felt good when I plugged in and the vertical collapse was gone, I wish I could have narrowed down the problem alittle more instead of shotgunning 4 parts but it feels good none the less.

Thanks for the help
Greg
 

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