Matsushita TM202G - Missing Green

kentmurphy

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Folks,

Looking for some advice. I have a TM202G monitor which is missing the color green.

I hit the tube with my CRT analyzer (Senscore CR7000) and all the guns are good.

I adjusted the green contrast pot and there was no change.

I recapped the monitor, but that did not resolve the problem.

I pulled and tested the green driver transistor (Q352) on the neck board and it tested fine.

I then decided to do some probing with my multimeter and compare the readings to a working Matsushita. I connected the black lead on my meter to pin 3 (see black arrow) of the connector on the video amp board. Next, I connected my red lead first to N12 and then to N13 (see red arrows).

https://skydrive.live.com/?cid=4127...cid=4127EA3A33B50049&id=4127EA3A33B50049!3773
https://skydrive.live.com/?cid=4127...cid=4127EA3A33B50049&id=4127EA3A33B50049!3772

The reading on the good monitor at N12 was ~4.5 vdc while on the non-working monitor it was 1.7 vdc. The interesting thing is that the readings for the other colors were also lower (~2.2 vs ~4.5 vdc) when compared with the working monitor. Yes, I realize the voltages from the game board can change as the intensity of the color changes, but I took my readings during the same point in the attract mode sequence.

Now for the questions. Am I overlooking something? What else can I do? Would you agree the problem seems to be isolated to the video amp pcb?

Thanks.
 
Maybe. There are two (maybe three) green pots, one on the little board on the left, and the other(s) on the neckboard. Have you tried them all?

You can also check the color processing IC and the input transistors/diodes you should fin on the input line traces...
 
Thanks mod ... the color processing IC is new to me ... what exactly are you referring to?


Maybe. There are two (maybe three) green pots, one on the little board on the left, and the other(s) on the neckboard. Have you tried them all?

You can also check the color processing IC and the input transistors/diodes you should fin on the input line traces...
 
Thanks mod ... the color processing IC is new to me ... what exactly are you referring to?

Oh yeah, I forgot the Piecoshita TM202 doesn't use a color processor. It uses various transistors to amplify the color.

So, you start by making sure you have voltage at your green input wire. Will probably show between 0.7-2.1 vdc, depending on the board you use for testing.

Then start checking your voltage at the transistors on the green circuit, in this case Q306, Q307, and Q308:

TM202-Videoin.png


Then you should check for the green output at N12. You could check this first if you want. If it's there, you can concentrate on the neckboard instead.

So, then check to make sure it's coming into the neckboard at C14 pin3:

TM202-Neckboard.png


Q352 is the green drive transistor. You can swap it with the blue one (Q351) if you're not sure if it's good. Then check R355 to make sure it's okay. Check continuity on traces and look for bad solder or cracks.

And all this is assuming that your green gun in the tube is actually good. Have you tried shorting the base of Q352 to see if the screen turns green?
 
BTW - you mentioned that all three color inputs are measuring lower than the working monitor, so it would be a good idea to check to see if the +12 coming into the video board is good. If it's low or high, it can cause all your transistors to rectify differently and give you improper voltages and missing colors. I had a G07 to repair that would only show red, and it turned out a resistor in the +12 fee had gone out of tolerance and was changing the +12 value, causing the blue and green to not get enough voltage to show...
 
mod,

thanks for all the suggestions ... I did a little more probing with my meter last night and since everything appeared to be good I decided to pull out my senscore one more time ... this time I discovered both the green and blue guns were having problems (bad tracking, low emission) ... I tried reactivating with no luck ... I'm going to do some more testing tonight, but I actually now think this tube is toast ... dammit!
 
I spent several more hours today with this monitor. To validate the tube was good and the chassis was bad, I swapped the tube into a new chassis and it's working fine.

Prior to doing this, I hooked the tube up to my CRT analyzer and rejuved and reactivated the blue and green guns. Yesterday and today when I tested the tube, both the green and blue guns had issues, but I think my rejuvenation helped.

Originally the tube tested good 4 months ago when I acquired my Millipede. Not sure what happened in the interim, but it appears my tube and chassis had issues.

Since I have a working chassis I'm not certain if I am going to fix the non-working chassis.
 
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