REPLACING THE RGB AMPLIFIER BOARD FET

Please read the DISCLAIMER prior to proceeding. This section deals with stuff that can kill you if you don't know what you are doing. Don't be an ass. Even a Barco is not worth dying for. If you don't meet the criteria described below, leave this procedure to a skilled technician.

RGB output stage failing

Failing FET symptoms
One of the most common problems with the 800 series is a FET on the RGB amplifier boards behing the tube necks failing . Usually the first sign of FET failure is image ghosting or streaking to the right or a number of diagonal retrace lines appearing in dark scenes. After some time, the tube will start getting brighter and brighter causing the problems associated with too high G2 settings. Most people wont notice the other problems at first and simply turn down the G2 pot. The FET will just get worse however and should be replaced as soon as possible.

Identifying RGB amplifier board problems
FET related problems are usually identified by swapping the suspected board with another as they are interchangeable. If the problem moves to the other tube you will know something is wrong on the amplifier board.

2SK511 Bastard FET From Hell

2SK511 FET
The FET that is often causing problems is a 2SK511 that is on the RGB amplifier board behind the tube showing the symptoms described in the previous paragraph. If you have moderate technical and soldering skills, you can replace this component yourself. If you don't possess these skills i HIGHLY recommend staying away from any of the DIY stuff on this page. Once you find that the FET on one of the RGB amplifier boards has problems, you might as well replace the FETs on all three boards as the problem is bound to occur on the others sooner or later. Unfortunately the 2SK511 is pretty hard to come by these days so if you can buy a couple at a time i recommend doing exactly that as you will probably need to replace another one in the future.

REPLACING THE FET
The following section describes the procedure for replacing the 2SK511 FET on the amplifier board. If you decide to take this mission and have not yet read our disclaimer do so now. If you have already read it, read it again.

The Tools

Tools you'll need

soldering iron

solder tin

solder sucker

some thermal paste

2SK511 replacement FET * duh! *

small screwdriver

a working brain

The amplifier boards are located behind the tubes

FET Location
The FET responsible for our nightmares is located on the RGB Amplifier board behind the tube showing the problem and is indicated by the label "Q6". The picture on the left shows a view on the internals of the Barco (tubes on top). As you can see each color channel has its own amplifier board.

Step 1
First turn of the projector, remove the AC cord and turn it on and off again to let the projector discharge. Wait another half hour just to be sure before proceeding. Remember that CRT projectors have high voltage circuits and contain many capacitors that can hold deadly charges even when turned off.

Step 2
Turn the screws holding the Amplifier board to the chassis frame counterclockwise to unfasten them. Gently disconnect the two cables connected to the board and remove it from the projector.

2SK511 FET often responsible for the trouble

Step 3
The FET we're replacing is the left one marked Q6 on the PCB. It is located behind the star shaped cooing fins and next to a small plastic coil. This is the only thing we are going to replace. DON'T TOUCH, TURN, OR TWIST ANY OTHER COMPONENT on the board. It could kill your tube. You may have to remove the star shaped cooling fins on the component in front of the fet to be able to remove the bolt and nut clamping the FET to the cooling plate. Be very careful doing that or you'll break the leads underneath it.

Step 4
Once you have removed the bolt, you can desolder the three leads of the Fet and remove it from the board. Use the solder sucker to remove the soldering tin so it can be taken out easily. The FET dissipates heat through a small piece rectangular piece of formica. You will need both this formica block as well as the small grey bus and metal ring to install the new FET so don't throw them away.

Step 5
Gently insert the new fet while keeping the formica block in place. Apply some thermal paste between the formica and the cooling plate as well as between the formica and the FET. You can remove excess paste later using a cotton swab. Fasten the bolt, nut, bus, ring and so on prior to soldering the FET or you'll have serious headaches getting it to fit afterwards.

Step 6
Gently solder the three leads to the board again. If you !^#&@! by soldering the leads together use the tin sucker to remove the soldering tin and start over. Make sure the leads are properly soldered, because if they're not you'll regret it later.

Step 7
Cut/clip off the remaining leads that sticks out from the soldering points of the board so everything looks the way it did before. Do a final check and don't forget to put the star-shaped cooling fin back on if you removed it. This fin can be a real bitch so be careful you don't break anything.

G2 and focus pots

Step 8
Put the board back into the projector and make sure both cables are properly connected again.

Step 9
Reconnect the AC cord and turn on your projector. Duck! heheh :-) If no zapping noises or smoke appears you can assume your Mighty Marvel Pose #25 and look cool.

Step 10
Set G2 to the appropriate level by setting the color balance of the projector to D6500, projecting a 0 IRE black image, turning brightness to 50 and contrast to 0 and turn the G2 pot gently until the raster just barely lights up. BE CAREFUL WHEN DOING SO! The G2 pots are located near the power supply that uses LETHAL voltages. Touching the wrong things CAN KILL YOU.

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