B&W Monitor Issue question

supadave1

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Ok, my monitor has this white bar that travels from top to bottom of the screen. Like some sort of interferance or ground issue. I've checked the wiring so many times, and I've even replaced some of it. I'm out of ideas. Take a look at the picture to see the white bar in question. Could there be a faulty cap causing this? Any monitor gurus have any suggestions. I just had the board repaired by Electroforge and the assured me that they never had the white bar issue during any of their repairs. Any help would be greatly appreciated. Sorry, I don't know the monitor model off hand.
 

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Those are hum bars. Most likely caused by bad caps on the power supplies in the monitor. What's the monitor model?
 
Black and White Motorola XM501.. Pretty sure, but I can't go check at this momment. When you say in the monitor,you don't mean in the tube itself do you? You just mean the chassis right?
 
If your game uses a seperate power supply for the gameboard then you've got bad electrolytic caps on it. If your game uses the optional +5 volt power on the monitor (if the monitor is so equipped) to run the gameboard then you have a problem in that power supply on the monitor.
 
i'll take a picture later and you can help me better understand. If you would pls..

Thanks.. I'll take tak later tonight.
 
Ooh. I'm the xm501 master! Meaning that my xm501 kicked me in the teeth for about 6 months so I've had a bad time of it. :) The big aluminum can capacitor is suspect. But on that monitor I would expect the hum bars to look a little different. So I suspect Ken is right about the game board. That's Stunt Cycle, right?

Check the following:
1) On the monitor chassis, measure the AC volts for +73 and +30 supplies. These can be most easily found on the pins around the edge of the chassis. You can connect the meter's negative lead to the chassis ground.) The less AC voltage the better.
2) On the game board, check the AC and DC volts going into/out of the LM309 regulator. Easiest way to do that is to clip the negative lead to the minus lead of the 8000uF electrolytic cap. Then check both ends of the big 10W power resistor with the red lead. At one end of the resistor, the DC voltage should be very close to +5V and the AC should be very small (ideally = zero). At the other end, the DC volts should be "higher" than +5V. Hopefully no lower than about 7.5V. The AC measurement will depend on the load.

Your problem is with one of these points. (or maybe a little of each)


Oh, BTW....for me, "monitor" means "tube + chassis". So yeah, I mean the chassis. Sorry. :)
 
I don' t think it's the game board at all. I just got it back from Electronforge. I sent it to them for graphic issues and these hum bars. They repaired the graphic issues but said they never experianced any hum bars on their stuff. They said they gave the board a solid check in every erea after they fixed the graphic stuff. I'll try and check the items you mentioned but I'm staying away from the game pcb itself. The game plays flawlessly right now.. Just them annoying bars.

There is a seperate power supply up near the monitor chassis.

I found some nice tech manuals on the monitor.. Says for hum, to adjust low voltage regulator, set to 73 if possible. Says there could be an open cap in the power supply or on B+ Buss feed points. Possible defective zener diode. (all that was greek as hell to me) I did find a pot in the manual that is on the chassis to adjust the 73V. I can at least test the voltage levels and adjust the pot. Beyond that I'll be lost.

Ooh. I'm the xm501 master! Meaning that my xm501 kicked me in the teeth for about 6 months so I've had a bad time of it. :) The big aluminum can capacitor is suspect. But on that monitor I would expect the hum bars to look a little different. So I suspect Ken is right about the game board. That's Stunt Cycle, right?

Check the following:
1) On the monitor chassis, measure the AC volts for +73 and +30 supplies. These can be most easily found on the pins around the edge of the chassis. You can connect the meter's negative lead to the chassis ground.) The less AC voltage the better.
2) On the game board, check the AC and DC volts going into/out of the LM309 regulator. Easiest way to do that is to clip the negative lead to the minus lead of the 8000uF electrolytic cap. Then check both ends of the big 10W power resistor with the red lead. At one end of the resistor, the DC voltage should be very close to +5V and the AC should be very small (ideally = zero). At the other end, the DC volts should be "higher" than +5V. Hopefully no lower than about 7.5V. The AC measurement will depend on the load.

Your problem is with one of these points. (or maybe a little of each)


Oh, BTW....for me, "monitor" means "tube + chassis". So yeah, I mean the chassis. Sorry. :)
 
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I don' t think it's the game board at all. I just got it back from Electronforge. I sent it to them for graphic issues and these hum bars. They repaired the graphic issues but said they never experianced any hum bars on their stuff. They said they gave the board a solid check in every erea after they fixed the graphic stuff. I'll try and check the items you mentioned but I'm staying away from the game pcb itself. The game plays flawlessly right now.. Just them annoying bars.

There is a seperate power supply up near the monitor chassis. If that is indeed corrupt are those hard to replace?

Ok, stick with the monitor for now. Just check the AC voltage at the +73V and +30V test points and report back. I don't know how the Stunt Cycle cab is wired, so I can't help much with that extra supply. What is it connected to? (input and output)
 
I will check those points and I'll get back with you on my findings. This will have to wait till tomorrow. You have been a big help and have given me a good avenue to start checking.

If you look at the tech manual http://arcarc.xmission.com/PDF_Moni...19in) and XM701-10 (23in) Service Manual.pdf page 3 you can see the diagram of the power supply which does make a little sense to me.

This manual http://arcarc.xmission.com/PDF_Monitors/Motorola_XM_Series_Technical_Repair_Manual.pdf has a trouble shooting section and hum bars is listed. Gives some things to check.

Ok, stick with the monitor for now. Just check the AC voltage at the +73V and +30V test points and report back. I don't know how the Stunt Cycle cab is wired, so I can't help much with that extra supply. What is it connected to? (input and output)
 
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That Tech manual is great. I used it a lot when I was trying to replace missing parts of my xm501. The caps that it mentions for hum/weave problems are in the big aluminum can on top of the chassis. There are 4 of them in a big roll of paper, foil, and tar inside the can. Measure the DC voltage on the B+ test point. Set it to +73V then measure the AC voltage there. If there's "a lot" of ripple there, it's a problem.

("a lot" is subjective. Let me know what you find and we can go from there.)
 
Ok, here is what I found.70V was reading 76.. 30V was reading 35.. I adjusted them and got them bot to be about perfect.. 70.3 and 30.4 that was as close as I could get. I think it did help the hum bars a little. I think they are a little bit less noticable. However, it didn't fix it. But it's a start. I think the big caps need replaced.. See pic upper left corner. Your thoughts?

I attched some pics of my xm501 chassis. I appreciate all the help so far.
 

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That should be 73V not 70V. But that's pretty close. Better to be too low than too high. Did you measure the AC voltages? Be sure the get the AC values so we know what to do next. Could be that your caps are as ok as they're going to get. Mine were and I had to look elsewhere for the problems.
 
I measured the AC from the wiring going into the chassis and it was reading fine. I don't remember the exact number I think 115-120 somewhere in there and it was steady.
 
I measured the AC from the wiring going into the chassis and it was reading fine. I don't remember the exact number I think 115-120 somewhere in there and it was steady.
No, I meant measure the AC value of the +73 and +30 test points.

Example:
Measure the DC value of the +73V supply.
Without moving your meter leads, switch the meter to read AC instead of DC.
What do you get?
 
When you say test points, do you mean the little numbered posts around the edge of the board.. cause that is what I did.. I put the ground to number 6 (chassis ground) and the hot to the other points (+73 +30's etc) they measured fine in DC mode. I also re-adjusted the 70 I mentioned up to +73.. When I switched my meter to AC and measred the same points all I get is 0.1 or 0. Nothing really.. Am I doing it right?

No, I meant measure the AC value of the +73 and +30 test points.

Example:
Measure the DC value of the +73V supply.
Without moving your meter leads, switch the meter to read AC instead of DC.
What do you get?
 
Seems right to me. Just to be sure, switch the meter leads and repeat the measurements. You should get the same numbers for the AC measurements and negative numbers for the DC measurements (eg. -73V). Some meters do AC in funky ways.

If the measurements hold up, it means that your monitor supplies are clean - with very little AC ripple. Better than mine in fact. So I think your problem lies elsewhere. Which brings us back to the game pcb. There's likely a power supply problem there. It could anything from the on board regulator all the way up the chain to the power transformer. So go ahead and measure the input and output to the LM309 like I described before.

Oh yeah. You mentioned a separate power supply, up by the monitor. Did you find out what that is for?
 
If you look at the picture, you can see the transformer and powersupply components to the left.. That is the powersupply stuff I was talking about when I said extra power supply. I measured the power coming into it (the white connecter leads there) and they are steady 120. I may just send this off to Chad and let him overhaul it. I'm just not sure what to check for next. I am very capable of installing new caps if a cap kit may be in order.

I emailed Elecronforge guys the ones that repaired the board. They said that they checked all of the board and everything was reading fine. They said they never got any hum bars on their equipment.

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IIRC, that's not an extra power supply. It's an audio board. Some games used it...some did not. Yours does not use it.

Edward
 
yeah, the little red board behind the transformer is the audio board.. if you notice the audio fuse is also pulled in the bottom left of the picture. but the cans at the upper left, transformer, and a couple of other components are power related somehow.

IIRC, that's not an extra power supply. It's an audio board. Some games used it...some did not. Yours does not use it.

Edward
 
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