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ViewSonic PT813-2M

 
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VintagePC
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PostPosted: Sun Jun 18, 2006 7:58 pm    Post subject: ViewSonic PT813-2M Reply with quote

Hello,
I have a PT813, and the problem seems to be that there is no blue in the picture- the entire image has a yellowish hue.
The problem isn't the input circuitry, as the OSD is also off colour. It was suggested to me that the problem may be the video AMP on the CRT neck board.
I've found that the blue is present, but it seems to be stretched all over the place, so it's faint. I can see bluish smudges on the raster to the right of the image.
I have pictures of the display if someone needs to see them.
I would really appreciate some help getting this monitor working.
Thanks!
VintagePC
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VintagePC
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PostPosted: Mon Jun 19, 2006 1:55 am    Post subject: Found more info Reply with quote

Okay, I've just done some internal signal swapping, mapping the red signal input to the blue and vice versa. The results are definite:
The blue signal is fine. This means that the problem lies on either the board at the base of the CRT, or the CRT itself(doubtful, as there is still blue present, in small amounts, so the tube is still okay.)
Could it be a bad blue ground line, or the blue deflection circuitry?
Which ICs on the neck board involve the blue signal? How do I check if they are bad? Is there any way to check if the blue deflection is not functioning?
Are there any suggestions, as it is definitely beginning to look like the AMP is bad. I am already scouting sources for a new one.
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PostPosted: Tue Jun 20, 2006 7:37 pm    Post subject: Reply with quote

There should be 3 transistors on the neckboard for Red, Green and Blue, are these soldered in properly? (are the socket solder joints good?) If you can find the R,G and B input wires for these swap the blue for another colour, then the blue should be strong and the other colour weak if your tube is O.K.

Let us know how what you find. Smile
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VintagePC
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PostPosted: Thu Jun 22, 2006 5:07 am    Post subject: Reply with quote

I've already checked those transistors. The solder joints seem okay.
I tested the tube's blue gun by grounding the pin with a 10K power resistor, and the picture turned blue, so the tube is okay.
I've narrowed it to the video amps and the mentioned transistors. Since the amps are the hottest ICs on the board, I'll replace those first, since a hot IC usually fails before a cold one.
If that doesn't solve it, I'll consider the transistors, since the PCB around them seems to be slightly darker. (heat, maybe?)
Anyone recommend a good substitute for them? the part number is A1433-6L
Thanks!
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