Author Topic: Trinitron computer monitor fault?  (Read 1838 times)

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Offline steve30

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Trinitron computer monitor fault?
« on: March 09, 2015, 08:26:23 am »
I have a Dell P790 monitor, with a 17" Trinitron tube, dating from 1999. I've haven't used it much sine 2008 when I changed to a bigger monitor, but it has always been quite reliable.

However, I went to fix some problems with a computer yesterday, and required the use of this monitor, and it started behaving weird. The image was shrinking horizontally, the brightness was changing, and it was flashing on and off. I made a 3 minute video of the problem here:

Does anyone have any idea what the problem could be? I haven't had chance to take the monitor apart and inspect it yet. Might do that later.

Many thanks.
Stephen Coates :)
 

Offline T3sl4co1l

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Re: Trinitron computer monitor fault?
« Reply #1 on: March 09, 2015, 03:37:08 pm »
Weeeeird!

Your problem may be similar to what I had; http://seventransistorlabs.com/Monitor/index.html

Take off the back cover and see what's inside.  Also, try to find the service manual if you can.  Likely, you'll have a main deflection board, or something like that.  The board contains voltages from 100V to 1500V, so... probe very carefully, with as insulating a stick as you can find!

The pincushion changing makes me think it's possibly a broken solder joint or SMT component near the horizontal drive (as was my case) or pincushion or S-correction circuits.  The failing intensity may be the same (i.e., video cutoff under weak horizontal conditions, to protect the tube).  Or it may be something completely unrelated (e.g., ~100V supply to the video amps going intermittent?).

Good luck!

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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Offline steve30

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Re: Trinitron computer monitor fault?
« Reply #2 on: March 10, 2015, 04:29:54 pm »
Thanks for the link. I'll have a detailed look inside the monitor when I get chance.

What is the best way to discharge the capacitors in a monitor?
 

Offline T3sl4co1l

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Re: Trinitron computer monitor fault?
« Reply #3 on: March 10, 2015, 05:32:37 pm »
A 10-100 ohm resistor will do fine, or a screwdriver if you're lazy... the HV you should probably leave alone, since you don't need to remove it.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline steve30

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Re: Trinitron computer monitor fault?
« Reply #4 on: March 28, 2015, 06:48:59 pm »
Well, I took the monitor apart, and cleaned out 15 years worth of dust  :D.

Unfortunately I couldn't see anything bad inside it.

The fault still seems a little bit intermittent. And today, the tube kept turning off (with the power light blinking fast). So I switched it off and left it to cool down, and now it is back to all the flickering as shown in the video.

 


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