BD701 convergence


I am having problem setting blue on green at the bottom of the screen.
The pj is ceiling mounted and red on green is perfect - fits almost in the middle of the scale. Any ideas what might be wrong? btw. crosshair is spot on.




Active Member

There are several things that could be causing this.

Is it possible to post a photo of the problem with the convergence test pattern displaying blue on green to let us see the problem more clearly?

I assume that you have no errors when you try to adjust convergence and that the convergence does have an effect, just not enough to align everything perfectly.

I know more about the technicalities of NEC CRT's but very little about Barco's. One of the Barco experts should be able to confirm or point you in the right direction. Please check with a Barco Tech before trying anything that follows.

1) Early in the Barco setup you use the remote to shift the raster about on the tube surface. Have a look in this area and make a note of the values. If they are massively different between the red and blue settings it could be that the raster neutral position is not set correctly. There are rotateable magnets on the tube which are used to centre the rasters with the electronics set at mid position. Re adjusting the magnets at midpoint just might solve the problem. This is not a job for the enthusiastic amateur as there is around 35000 volts in the High Tension circuits of a CRT projector. This probably a job for the professionals.

2) There are other magnets around the tube which control the shape of the electron beam and the centring of the beam within the flare. Defocussing the tube allows this effect to be seen. Again a job best left for the experts for the same reasons as above. Once again something where incorrect adjustment might just cause the problem you are seeing.

3) The yolk which controls the convergence on the blue tube could be faulty. This could be checked by swaping the wires with the ones for the red tube at the deflection board. If the fault moves to the red tube you have your answer.

4) On Barco projectors the magnetic rings at the rear of the tube are often marked with red paint. If these marks do not appear to be aligned there is a good chance they have been accidently bumped and will need to be adjusted.

Options 3 or 4 could probably be checked by an enthusiatic amateur but make sure you power down the projector first. Switch it off at the wall but leave it plugged in. In that way the chassis will still be earthed.

The above are merely possibilities, I do not recommend you go into the "guts" of your projector but suggest you get a professional to try some of the above on your behalf.

better safe than sorry.


My knowledge of this machine is pretty limited, as I worked on the 8xx and 1xxx series quite a bit more, but on most of those there were vertical and horizontal pots on the deflection boards. There may be something similar on this model as well. Someone else may know more conclusively.


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