Neotec NT-1431 (Medalist Dart Star monitor) pin cushion issues

jimbodeanny

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Neotec NT-1431 (Medalist Dart Star monitor) pin cushion issues

I just finished recapping the 14" Neotec NT-1431 VGA monitor that's in my Medalist Spectrum Genesis dart board. I used KenLayton's document as my guide (https://www.arcade-museum.com/manual...ir guide.pdf)

I replaced all of the electrolytic caps Ken listed, including the filter cap. I also replaced the 4 "problem" resistors that were mentioned.

Everything works great, except I'm now getting some serious pin cushion issues. I basically get the hourglass shape on all 4 sides. The pin cushion POT doesn't do anything. I checked the POT and it tests fine and the solder is good. All other controls function properly.

Are therer perhaps some other caps that need to be replaced?

Thoughts?

Thanks!

-Jim
 
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I just finished recapping the 14" Neotec NT-1431 VGA monitor that's in my Medalist Spectrum Genesis dart board. I used KenLayton's document as my guide (https://www.arcade-museum.com/manual...ir guide.pdf)

I replaced all of the electrolytic caps Ken listed, including the filter cap. I also replaced the 4 "problem" resistors that were mentioned.

Everything works great, except I'm now getting some serious pin cushion issues. I basically get the hourglass shape on all 4 sides. The pin cushion POT doesn't do anything. I checked the POT and it tests fine and the solder is good. All other controls function properly.

Are they perhaps some other caps that need to be replaced?

Thoughts?

Thanks!

-Jim
Paging Ken Layton...
 
Check the modulation diode (the diode with the cathode connected to the anode of the damper diode and the anode to ground) in the flyback HOT area (or post pics of the chassis).
 
I would need a closeup of the area behind the flyback and if possible also the solder side. Schematics would be even better.
 
I would need a closeup of the area behind the flyback and if possible also the solder side. Schematics would be even better.

I'll take some pictures this evening. I have not been able to locate any other documentation other than what Ken documented.
 
Double check the value of C315 and C316. C316 should be 22uf bipolar.
 
I would inspect your soldering around Q304. Looks like you may have a bridge.
 
I would inspect your soldering around Q304. Looks like you may have a bridge.

Thanks. Double checked that area it's fine. No bridged traces. I went reflowed the pin cushion POT as well as the headers to no avail.
 
The chassis doesn't seem to have an east west correction circuit like say a WG K7400, a Nanao MS9, a Hantarex Polo or any other chassis with said circuit so I wouldn't expect it to have a pincushion pot or a width pot and clearly doesn't have the diode I mentioned. It looks like width is adjusted with a coil (the one with the white knob) and has a jumper for wide/narrow positions so it has all the features of a chassis without east west correction like a K7000 or a Nanao MS8-26 and it's weird to hear it has a pincushion pot and without seeing how this correction is done I can't say anything about it. Do you get any change by moving the width jumper from W to N and adjusting the width coil? Did it have this issue before doing the cap kit?
 
The chassis doesn't seem to have an east west correction circuit like say a WG K7400, a Nanao MS9, a Hantarex Polo or any other chassis with said circuit so I wouldn't expect it to have a pincushion pot or a width pot and clearly doesn't have the diode I mentioned. It looks like width is adjusted with a coil (the one with the white knob) and has a jumper for wide/narrow positions so it has all the features of a chassis without east west correction like a K7000 or a Nanao MS8-26 and it's weird to hear it has a pincushion pot and without seeing how this correction is done I can't say anything about it. Do you get any change by moving the width jumper from W to N and adjusting the width coil? Did it have this issue before doing the cap kit?

Thanks for the response.

I haven't tried changing the jumper, but the width coil (knob) works fine and gives lots of adjustment.

Before the cap kit, it had a mild form of the pin cushion issue. I didn't try adjusting the POT prior to the cap kit.
 
I changed the jumper from W to N and the issue is still there. I had to make a few size/position adjustments, but the pincushion/hourglass issue still remains.
 
Since nobody seems to know anything about this monitor except KenLayton, I've decided to replace this monitor with an LCD.

If I hear back from KenLayton or someone else with repair knowledge, I'll try tackling it again. In the meantime, this one will be stored for a rainy day.
 
The jumper between R428 and C417 is a bit confusing as it effectively bypasses the secondary of T403. Maybe the winding was open and someone did that as a stop gap?

I know you say you checked it but the picture really looks like there is a base to collector bridge on Q304.
 

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I know you say you checked it but the picture really looks like there is a base to collector bridge on Q304.

Ah, I see what you mean now. I'll recheck it this evening.

Thanks
 
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Reinspected Q304 and can confirm that there's no solder bridge. The photo I originally took must have been at a bad angle that made it look that way.

Here's another image...


 
Ok so that leads me back to the secondary of the pin transformer. Take a look at that jumper and see if it looks deliberate. There is just no way the PCC will work with a jumper across the secondary. However if the transformer had burned or opened up someone may have jumpered it.
 

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