Samsung syncmaster 793mb

[ratdude747]

well, i have no idea on this one.

my mom used to use a samsung syncmaster 793mb... but it had issues (below) and she got an extra emachines crt to keep her happy.

ANYWAY... i have it still... and i wonder if it is fixable.

it gets random horizontal brown bars and lines on the display. they are constantly changing. annoying.

iirc there is an ic or two to blame....

i am the biggest n00b on crt work... isn't there a way to safely open one of these up? it has been unpowered for about 5-6 months at least.

how would one open and service a unit like this? is there a fix for the brown lines?

[ratdude747]

Re: Samsung syncmaster 793mb

my research says it is an issue with cold joints on the control board.

any idea on how to safely open it?

[Wizard]

Re: Samsung syncmaster 793mb

Ratdude, not the control board and bad solder joints is not their problem, I have not seen any with bad ones and there is no capacitor issues either, read on and I included instructions on opening this case.

There was bulletin but it was not the fix, I figured out the real problem for the brown lines is poor grounding of IC *even* there is a grounding pin on the IC but actually there is 2 pins one is not hard grounded, (connected to the actual die, other one pin is to the tab. Problem is in CRT board (this small board on back of CRT's tube).

The main issue is poor electrical grounding between heatsink and the CRT driver IC. Very *specific* problem is gum on the foil sticker that covers the IC is breaking grounding conductivity.

Undo 2 philips #2 screws at bottom, put CRT face down on padded surface (blanket suffices). Take a flat tool (has to be metal) that fits into top slots where back cover and front bezel meet, there are 2 small slots. Push down the tool FIRMLY through this slot till you hear CLICK at same time pull back case upwards, do the same to other catch.

The most reliable fix: Take off CRT board (red and white HV focus wires comes out of CRT socket (push down firmly on the small nub and wiggle the wire out. (red and yellow or white IIRC) and disconnect wires to the CRT board. Unsolder cover from PCB and undo 2 screw (do this first). Unsolder the IC pins this is bit harder because pins are in zipzag pattern and very close together and two twisted pins of the heatsink. Extract this heatsink with IC attached. Undo the screw of the IC clamp. Extract this IC wrapped in sticker foil. Clean off white heatsink paste from both. Peel back foil only the back of IC where IC sits on the heatsink is. Clean gum off the foil *completely* with ear swabs and acetone (real deal not the nail paint remover), do the same with IC's thermal patch. Lay the foil back on the IC (no heatsink paste there!, we need the electrical connection!) and apply bit of heatsink paste on the foil and put IC back into the heatsink, clamp loosely. Reinstall heatsink with IC to PCB, solder two heatsink tabs and clamp the IC. Finish soldering the IC, CAREFULLY inspect for no solder short by using flashlight to backlit the PCB and look at it easier this way. Reassemble.

The MOST important key is NO paste between IC and foil, same with no gum sticker. Only between foil and the heatsink.

I have fixed SO many of those.

Cheers, Wizard

[ratdude747]

Re: Samsung syncmaster 793mb

any safety precautions io need to take?

[Wizard]

Re: Samsung syncmaster 793mb

Just take care that you don't needlessly touch hot side power supply. And you are not going to pull the chassis since it is not needed to be removed and HV cable (fat red cable ends in grey suction cup) is not needed to be unhooked. Chassis is in metal pan. Your concern involves the CRT board only, the focus HV wires (two thinner red and white cables is discharged) due to dynamic focus circuit draining any charge left off.

Cheers, Wizard