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Main => Monitor/Video Forum => Topic started by: smartbomb2084 on February 01, 2014, 06:39:04 pm

Title: WGM 2775 RFI
Post by: smartbomb2084 on February 01, 2014, 06:39:04 pm

Been working on a 27 inch K7500 in a Golden Tee cabinet of and on for a few months now... 

It was blowing the HOT when you shut the monitor off...I toasted 6 of them.   I finally got it to stop... one of the parts I changed out of desperation was Q703, the Horizontal pre driver.. It has a small glue-on heat sink that I reinstalled...

While the monitor was out of the game and running... I put my finger on the heatsink of Q703 to feel just how hot it was getting... It was cool to the touch.

I have the radio on in the shop tuned to a local sports AM station ... when I touch the heatsink of Q703...WHICH IS NOT GROUNDED... it causes a high pitch tone over the radio...

This seems odd and cool at the same time... Is it a magnetic field being induced through the transistor by my finger or is it pure RFI or a little bit of both?

The heatsink is just glued to the plastic case of the transistor and not physically connected to the deflection board... how is this happening?   Is it a problem in the monitor that still needs fixed?

The monitor looks awesome otherwise.

Title: Re: WGM 2775 RFI
Post by: buffett on February 04, 2014, 05:17:39 am

can you post the Part # of Q703 so i can order them.

also can you elaborate on the other suspected parts you changed.

i need to try this fix.

i have 2-3 chassis doing the same thing and have not found the problem.

the H.O.T. is not cheap to keep toasting.

Peace
Buffett

Title: Re: WGM 2775 RFI
Post by: smartbomb2084 on February 04, 2014, 06:03:42 pm

Q703 is a 2SC2482... I got 5 of them for $6 delivered through a 'Best Offer' on ebay.

http://www.ebay.com/itm/2SC2482-Toshiba-Transistor-LOT-OF-5-PIECES-/161048194023?pt=LH_DefaultDomain_0&hash=item257f386be7#ht_1239wt_987 (http://www.ebay.com/itm/2SC2482-Toshiba-Transistor-LOT-OF-5-PIECES-/161048194023?pt=LH_DefaultDomain_0&hash=item257f386be7#ht_1239wt_987)

I capped this monitor about 2 years ago but it was an 'In House' kit and not complete.

Along with Q703 I changed...

R120 in the PS.. it was open.

R727... the resistor color bands were pretty much completely burned off...

C729... 10UF/50V Bi-Polar cap that was not changed the first time around.

C734... also not changed the first time around.

I guess one or more or all of these parts stopped the HOT failures...Since they were all changed at once I can't narrow the problem down any further.

On a side note... the RFI touching Q703 does not happen with the monitor re-installed int the cabinet.

Hope this helps man...PEACE.

Title: Re: WGM 2775 RFI
Post by: buffett on February 04, 2014, 06:09:21 pm

thanks for the rite up.

this will help try and narrow down the problems i am having.

Peace
Buffett