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K4900 Color Bleeding and Volume Question
Question from Jeff: Hey Guys. I have a Super Pac-Man cocktail table, which did not work when I got it and I have managed to fix everything that was wrong and am loving playing it! One of the things that was non-working was the display, it was all white. So I re-capped the monitor (with a kit from Zanen) and it came right to life. The picture needed adjusting, but I adjusted it and it was fine.
One of the problems that needed adjusting was the red was “bleeding” downward (which I believe is actually to the left, since it’s a vertical display). I dialed down the Red Cutoff and CRT Drive as low as they would go and the “bleeding” went away. But after the machine was on for a little while, it would start to come back AND in less and less time. To where now, it starts almost immediately when I turn it on. I have the Black level turned as low as possible also. Each of these controls will make it worse when I turn them up, but I have them all turned all the way down as low as they will go.
I’ve seen your video “Arcade Repair Tips – Adjusting An Arcade Monitor” and in it you say something about “Contrast” but there is no “Contrast” adjust on this monitor that I can find. The monitor is a Wells Gardner K4906.
#1 – Do you have any ideas on how to solve this problem please?
And…
#2 – I want to stick a volume pot in the wire to the speaker, mounted on the side of the cab so I can easily turn it up and down from “play position”. Do you have a recommendation of what pot to use and any info on how to wire it? I believe that on a 3-pin pot, pin 1 gets connected to the speaker (+) coming from the PCB, pin2 then goes to the (+) terminal on the speaker itself, and pin 3 (along with the body of the pot itself) is connected to ground (which is what speaker (-) is also connected to). But if you know, please let me know if that’s wrong, and again if you have a recommendation of what pot to use?
THANK YOU THANK YOU for anything you can tell me!
Jeff
1 answer
Response from Jonathan: Jeff,
So, the red color bleeding you are experiencing is usually caused by a bad part on the circuit for that color. Make sure that you check the transistors located at Q203 and Q206 as well as the diode at D207. More than likely the issue is in one or more of these components. If you continue to have problems after checking these parts, you might check for cold, cracked, or broken solder joints/traces starting at the red input pin where the signal connector from the main board connects to the monitor and follow it through the rest of the chassis.
On the volume question, you’re description of the wiring sounds correct. With that said, we recommend using the Solderless 25-Ohm 3-Watt Rheostat Kit from Holland Computers as it just makes the installation a breeze. This kit comes pre-wired to be used for volume (no soldering required) and also has a wiring diagram that shows you exactly how to hook it up. Also, Holland Computers is having a Memorial Day sale. You can get 15% off when you use coupon code MDAY2019 at checkout through May 31. We have worked with and ordered from Bill Holland and his team on numerous occasions and have always been impressed with their professionalism and quality.
Hope that helps. Thank you for your question and good luck with your repairs.
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