Wells-Gardner U2000 problem

segundosombra

Cheng's Errand Boy
Joined
Jul 29, 2004
Posts
114
Hi all,

I have a problem with my wells gardner monitor. I replaced the horizontal transistor in order to get working the chassis. After a few days it got faulty. I have replaced that transistor several times and I got the same result. I don't know what to do.

If anybody know how to fix this problem, please help me.

Thanks in advance.
 

channelmaniac

Mr Neo Fix-it
15 Year Member
Joined
Nov 29, 2005
Posts
4,275
Make sure you check out the high voltage caps and any diodes coming off the secondary circuits of the flyback transformer. Those tend to go leaky and cause the transistor to run hot & fail early.

RJ
 

ttooddddyy

PNG FTW,
Joined
Nov 29, 2001
Posts
8,335
Are you using the same type transistor or a substitute, if a sub are the specs adequate for the application. They should prefereably be higher.

If there is a mica washer between the transistor and the heatsink make sure there is no break down of insulation there.

Make sure to tighten the transistor well to the heatsink and use silicon heat transfer compound for good measure.

When the board is running tap around the horizontal output stage with an insulated screwdriver to check for dry joints, if you notice any instability(jumpy pic or intermittent noise or line collapse) you need to locate the poor solder points, this often leads to repeat failure.

Check the +B, if too high the horizontal output device may overheat and fail.

Any noises coming from the flyback transformer, like hissing or crackling ?breakdown here may also lead to hot failure.

It is possible that the hor oscillator going way off speed could cause this, check that the hold pot is not scratchy, even a cap kit around the horizontal osc/sync stage may help.

Also breakdown of the insulation on the deflection yoke windings can be a problem, may be worth removing for a look see.
 

segundosombra

Cheng's Errand Boy
Joined
Jul 29, 2004
Posts
114
Thanks guys for the reply.

@ttooddddyy: since I don't have too much knowledge about it... how many volts should I get from +B?
 
Last edited:

ttooddddyy

PNG FTW,
Joined
Nov 29, 2001
Posts
8,335
TIP- do not measure it on the collector of the horizontal output transistor- it will fry your meter ! Measure it at the cathode of the +B rectifier diode.

I do not have a manual for that model, but you should see it clearly marked on the schem. Its usually 120-130 volts. It is critical that it is set correctly.
 

segundosombra

Cheng's Errand Boy
Joined
Jul 29, 2004
Posts
114
OK, after several days testing my thing I can say it works fine. I just changed that transistor by another one with higher specs and I isolated it better.
Now I am trying to fix a screen problem... the left half is brighter than the right half... can you guys help me again?

Thanks
 

ttooddddyy

PNG FTW,
Joined
Nov 29, 2001
Posts
8,335
Good news.

Regarding the other problem, two things to check out.

180 volt supply to the video output stage, if low try the 10 uF smoothing electro.

Improve video grounding by running seperate connection from mobo ground to monitor ground.
 

segundosombra

Cheng's Errand Boy
Joined
Jul 29, 2004
Posts
114
Hi ttooddddyy!

I tried your tips but screen remains the same.

Here are pics of the screen showing that problem, maybe these are more elocuent than me:

14.JPG


15.JPG


Is there any other way to fix it?



Thanks
 

channelmaniac

Mr Neo Fix-it
15 Year Member
Joined
Nov 29, 2005
Posts
4,275
Also, what was the original part number transistor... and what is the part number you replaced it with?

RJ
 

segundosombra

Cheng's Errand Boy
Joined
Jul 29, 2004
Posts
114
Yes, that is BU2520AX and I replaced all caps that channelmaniac mentioned... still not working fine.

Any other sugestion, please?
 

ttooddddyy

PNG FTW,
Joined
Nov 29, 2001
Posts
8,335
segundosombra said:
Yes, that is BU2520AX

Its touch and go on the wattage rating of that device, thats the price to be payed for the isolated case ;) Anyway I wouldnt worry too much about it at this stage.

2SC 3686 = 1500/800v...7A...120W
BU2520AX = 1500/800v...10A...45W (lower wattage rating due to the isolated package)

Any other sugestion, please?

So you have done a full cap kit ?
 

ttooddddyy

PNG FTW,
Joined
Nov 29, 2001
Posts
8,335
What about the 10 uF which smooths the 180 volts supply to the rgb video outputs.

What voltage do you have there ?

This does look cap related or maybe a leaky signal diode in the video blanking.
 
Top