Looking for some help with Hitachi 29" GMK Monitor

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Nat
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Looking for some help with Hitachi 29" GMK Monitor

Post by Nat »

Hi,

Hopefully an expert can offer some advice, I have experienced a loud high pitched buzzing from my Hitachi 29" GMK monitor when powered up, it is an annoying constant noise.

I finally decided to remove the monitor from the cab to investigate the cause of the noise, I initially thought it was going to be related to the windings on the yoke, however after creating a cardboard listening tube I finally located the component on the chassis making the noise, it is the part in the below pictures and it is marked L707 on the silkscreen print on the PCB.

20211017_162504.jpg
20211017_162513.jpg
20211017_162525.jpg

Firstly what is it? (My guess is a transformer)

Secondly can a replacement be brought? I have no problems removing this and re-soldering another onto the PCB.

If not is there any technique to quieten it down such as potting it or using conformal coating on what I assume is the windings under the tape outer?

Thanks for any advice anyone can offer.
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Re: Looking for some help with Hitachi 29" GMK Monitor

Post by nem »

Correct, it's a transformer for adapting to a different specced yoke that the chassis wasn't originally designed for.

I don't think you'll find another compatible transformer, so I think that just leaves the option of sealing the unit somehow.
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Re: Looking for some help with Hitachi 29" GMK Monitor

Post by PrincessPrinPrin »

Apparently it's a coil that goes in series with the horizontal yoke when the monitor runs at 15KHz and it's disabled when in 24KHz.
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Re: Looking for some help with Hitachi 29" GMK Monitor

Post by Nat »

Many thanks for the replies and help so far, your assistance is very much appreciated as this is well outside my knowledge area.

However it never rains but it pours.....after putting it all back together and powering up the CRT screen is now dead, no neck glow on the tube, and a constant tick tick tick noise.

With my very limited knowledge would it be the HOT that has failed?

I've also had great difficulty in actually locating the HOT on the chassis, I think its the component in this image:

20211018_161515.jpg

My assumption this is an 2SC4589?


For more information this is the tube:

20211018_151451.jpg

This is the exact model on the monitor frame:
20211018_164433.jpg
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Re: Looking for some help with Hitachi 29" GMK Monitor

Post by PrincessPrinPrin »

Measure resistance from the middle pin of that transistor to the heat sink it's mounted on (or to the right leg). Low ohms means the transistor is likely shorted.
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Re: Looking for some help with Hitachi 29" GMK Monitor

Post by Nat »

Thanks for the help, I will check out the transistor.
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Re: Looking for some help with Hitachi 29" GMK Monitor

Post by nem »

Are you sure you haven't missed plugging something in? Sounds odd that it would before work and not now.

PrincessPrinPrin wrote: October 18th, 2021, 1:04 pm Apparently it's a coil that goes in series with the horizontal yoke when the monitor runs at 15KHz and it's disabled when in 24KHz.

Oh.
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Re: Looking for some help with Hitachi 29" GMK Monitor

Post by Nat »

Thanks for the help, I will double check all the connections over again as it is now on my bench, I just need a spare hour or so.
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Re: Looking for some help with Hitachi 29" GMK Monitor

Post by Nat »

Just a quick update, I finally managed to get a replacement HOT had to wait for delivery from the USA as I sourced a genuine Hitachi part, anyway I have fitted the new one and I am back up and running.

Now it is time to try potting the transformer to silence it, any suggestions? my thought was 3D print a case using PETG and then place the transformer into the 3D printed case (I have already de-soldered it from the PCB) and then fill with potting compound.


This is the blown HOT
20211123_194645.jpg
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