Author Topic: Need Guidance on K4900 (Read 4558 times)

edwardvci · « **on:** April 22, 2005, 10:47:26 am »

I have been reading this board for over a year now. Have built my arcade system from parts from here to there. But I have seemed to run into a small snag on my current project I am in the process of building a NBA Jam game for my church gym all the parts were going good until I got this "working" 19" monitor of eBay

Ken Layton · « **Reply #1 on:** April 22, 2005, 11:30:30 am »

Your computer backup supply may not be 100% on the 60 cycle frequency nor have enough 'oomph' to power a 19" arcade monitor.

Can you post a picture of what was actually sent you?

A Wells-Gardner 4900 series monitor definitely requires an isolation transformer. They are also well known for having many bad solder joints on the main board and needing a capkit. Some vertical problems are related to bad (dried out internally) capacitors. Once in a while one or both of the vertical output transistors fail, but IMO I don't think this has happened in your case.

edwardvci · « **Reply #2 on:** April 22, 2005, 11:58:28 am »

Heres what I got. I am also trrying to get a isolation transformer

Thanks

Ken Layton · « **Reply #3 on:** April 22, 2005, 05:51:24 pm »

That's a 4900 series all right. It looks like it still has all original capacitors in it, too. I'd order a capkit for it for sure.

edwardvci · « **Reply #4 on:** April 30, 2005, 10:43:48 am »

I got the cap kit, installed it with no problems. still got the same problem. (pic below) All caps are replaced except the really big one and c366 ??. C308 had a 3.3uf in it but I replaced it with the 2.2uf like the schematic said. Not sure what to try next have tried the pots but they don't change much. Thanks

I Also have the isolation transformer now

Ken Layton · « **Reply #5 on:** April 30, 2005, 11:41:16 am »

Check resistor R313 (470 ohms, 7 watts) with an ohmeter. It is the vertically mounted one on the corner of the main circuit board. It may look ok by eyeballing it, but checking it with a meter is what's needed. This resistor can go open circuit which will kill the vertical deflection circuit. You will need to unsolder one lead of this resistor to test it.

Early production runs had either a 750 ohm 5 watt or a 1,000 ohm 5 watt resistor installed at R313. Wells-Gardner changed the value to 470 ohms 7 watts for improved operation/reduced failures.

Sometimes one or both of the vertical output transistors can fail.

edwardvci · « **Reply #6 on:** April 30, 2005, 04:54:50 pm »

Its 750ohm and its reads good out of curcit. How can I check the vertical

edwardvci · « **Reply #7 on:** May 03, 2005, 09:36:15 pm »

Ok, Found another vertical transistor in an old 13" that works. Remover it. Checked it with my transistor checker that i forgot I had (18+ years ago you forget the things you have) It checked fine took the 2 out of the 4900 chassis and checked them they checked good. Even tried the the one I found and one of the old ones and saw no change whatsoever. Not sure what I should check next. Thanks for any advice..

dabone · « **Reply #8 on:** May 03, 2005, 09:43:18 pm »

Go to randyfromm website, (just add the .com)

Goto the tech department, then to experimental tech dept.

Grab the 4900 trouble shooting guide.

Later,
dabone

edwardvci · « **Reply #9 on:** May 03, 2005, 09:59:51 pm »

Thank you I have see references to this in other threads and had been to the page once before and could not find it. But this time I found it with searching the page for those words. Could he put it in any smaller print at the bottom of the page?

Will try this and see where it goes. Thanks

edwardvci · « **Reply #10 on:** May 03, 2005, 10:53:55 pm »

Well The flow chart helped but it looks like I may have a bad IC because everything else checks out. O well off to find a chassis on ebay

Grauwulf · « **Reply #11 on:** May 03, 2005, 11:24:00 pm »

Why would you go through all the trouble of testing everything only to not bother replacing one bad component that you found? Replacing that one chip will cost you a lot less than a replacement chassis will.

edwardvci · « **Reply #12 on:** May 04, 2005, 08:35:17 am »

Well after I slept on it, I Decided to get the IC and give it a shot. Just was a little discouraged after doing all the other with no change.
But I am now determined to get this working. Am going to my local electronic shop to get the ic today. We have a NTE dealer in town who carries a large selection so I should be in luck.

Grauwulf · « **Reply #13 on:** May 04, 2005, 11:37:46 pm »

I know it can be frustrating, I am going through the *exact* same problem with a K4900 form my Road Blasters right now. I am down to the same conlusion you are, I have a fried IC. Luckily I have a K4900 with a bad flyback I can cannibalize for parts. Stick to it, fixing and learning about the machines is the best part of the hobby. Well it is for me anyhow.

edwardvci · « **Reply #14 on:** May 09, 2005, 10:05:37 pm »

Grauwulf, replace the IC I still no luck. Hope your having better luck with yours. I'm stuck at the moment due to no scope.

Grauwulf · « **Reply #15 on:** May 10, 2005, 06:13:01 am »

Nope, no better luck here either. I have a scope, I just haven't had the time to sit down and test anything yet.

Karetaker · « **Reply #16 on:** May 11, 2005, 03:40:55 pm »

This may be a dumb question (forgive me if it is) but did you check the pot?

edwardvci · « **Reply #17 on:** May 12, 2005, 07:48:39 pm »

Is the yoke on me?

Just thought what if the yoke is bad? I checked with meter and I have R/Blue 2.8 ohms and green/yellow is open. I guess this is causing my problem?

( at work I'm the one who asks, "are you sure its plugged in???")

Grauwulf · « **Reply #18 on:** May 12, 2005, 11:08:50 pm »

I wish mine was as simple as that. I know my tube is okay as I have tested other K4900 chassis on it. It's good to know what's causing your problem though.

Ken Layton · « **Reply #19 on:** May 13, 2005, 12:01:42 am »

Nothing on the green & yellow? I'd say it was open allright.


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