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Author Topic: Ducksan Type 55 - Merit Megatouch XL Question  (Read 2686 times)

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yotsuya

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Ducksan Type 55 - Merit Megatouch XL Question
« on: February 27, 2012, 09:27:33 am »
OK, I picked up a Merit Megatouch with a dead monitor. When I got it home and plugged it in, I verified that the board works and puts out video, but the monitor itself doesn't seem to power up (the touchscreen works, though). There's no neck glow, and the monitor itself put out a buzzing noise.

I did some research on Merit's website, and it indicates that in a lot of cases, c804 is a cap that changes values over time and is usually the main culprit with power issues, and that I should replace it (along with a few others) with a larger value cap. I did that just for c804 last night. I fired it back up, and no luck. I still get the same buzzing noise, and no neck glow. I can still replace the others caps, but I was wondering if the buzz is an indicator that something else is bad. I can't pinpoint where it's coming from, so that's an issue because I'm not sure what to replace. It's interesting, too, because when I power down, the buzz doesn't stop immediately but powers down as well. It reminds me of a fan gradually shutting off, if anything.

I shot some video of the monitor. The buzz you hear in it comes from the monitor. If anyone has any insights, I would appreciate it. This is my first attempt at CRT repair, so I really want to learn from this.



Thanks!
« Last Edit: February 27, 2012, 12:50:19 pm by yotsuya »
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grantspain

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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #1 on: February 27, 2012, 04:30:42 pm »
i would suggest reading the HOT with a muiltimeter

yotsuya

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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #2 on: February 27, 2012, 04:56:41 pm »
GrantSpain-

Thanks for the tip. I have a multimeter, but I confess that I am not proficient with it. Any suggestions on what to set it to, as well as how to test the HOT?
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grantspain

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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #3 on: February 27, 2012, 05:17:30 pm »
the hot will be something like a bu2520 or 2sc5144 located on the flyback heatshield,set multimeter to diode test and read centre leg to heatshield-dead short is bad

yotsuya

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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #4 on: February 28, 2012, 12:07:28 am »
GrantSpain-

Thanks. I did try one thing tonight- I read Ken Layton's excellent writeup on repairing these monitors. One suggestion called for replacing one of the resistors. I had a spare of the type he suggested replacing, so I did- but nothing changed. I'll test the HOT next time it's set up. I take it I put one end of my multimeter to the center leg (say, the red one, and the other end (the black) on the actual heatshield? If I do this, and I get nothing coming up on the meter, this means the HOT is bad?
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grantspain

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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #5 on: February 28, 2012, 09:27:06 am »
reading the HOT centre leg to the heatshield should give a reading like a diode,open circuit with the probes connected one way round and something like 0.504 the other way

yotsuya

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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #6 on: February 28, 2012, 09:41:21 am »
Thanks, I'll try it tonight. If I get no reading, should I then presume the HOT is bad? Is that something I can replace?
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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #7 on: February 28, 2012, 10:03:28 am »
Thanks, I'll try it tonight. If I get no reading, should I then presume the HOT is bad? Is that something I can replace?
well as long as you are reading the correct transistor,if its faulty expect dead short both ways
yes its something very easy to change as long as you know how to solder and how to discharge a crt and remove a monitor chassis safely

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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #8 on: February 28, 2012, 10:08:52 am »
Unless this monitor has a self-discharging function, I'm not sure that power's getting to the tube. I get nothing when I remove the anode cap, even if it was just plugged in a minute earlier. I would expect something. There's no glow, no static- I have a decased 19" CRT in one of my cabs and you know when that  :censored: is turned on.

I just wish I knew what the source of that buzz was.
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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #9 on: February 28, 2012, 11:50:41 am »
the buzz is possibly a transformer under load

Ken Layton

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Re: Ducksan Type 55 - Merit Megatouch XL Question
« Reply #10 on: February 08, 2013, 11:41:58 am »
Due to the cabinet design, the electrolytic capacitors on this monitor bake dry real fast. It is strongly suggested to replace all the electrolytic capacitors on this monitor.