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Sjouke Burry[_2_]

wrote:
There's something strange on the RGB board!

There are 3 sets each consisting of:
2 BF871 transistors
1 390 Ohm 2W resistor
1 trimmer

But! The 3rd one, where the blue wire goes, has BF869 transistors and
a strange resistor without coloured bands. The trimmer is adjusted all
the way to one end, unlike the other two. On the solder side, I can
clearly see the brown remains of a rework (burned flux, I think) under
the resistor and the 2 transistors.

So, copy one of the good channels and undo the sloppy work.
for a quick test, swap the green and blue input wire, to see
whether the board has an error, or the fault is in a previous circuit.