Re: TECH: 13 inch Amplifone! HELP!!

IF all 3 bases are connected together and IF ANY
of the 3 transistors were shorted or leaky the result
would be to turn on all 3 beams.

Take out the transistors on the neck board. The result
should be a black screen. If instead you have one color
hard on there is probably a shorted gun (heater/cathode
short)---but not likely because that wouldn't cause the
whiteout you have now.

IF you can't achieve black with all 3 transistors out you
either have no voltage to the cathode pull-up resistors
(must be >90 volts positive) OR grid 1 isn't grounded
(bad pin contact??) OR high voltage is too high (but
you already checked that OR grid 2 is too high due to
a gassy CRT or bad contacts or defective grid 2 (screen)
pot circuit.

Thomas43@aol.com wrote:

> Yeah, All the vectors are on full bright. There is no RGB data getting to
> the monitor, because those wires are not connected at all, anywhere.
>
> I looked over a regular Amplifone board, and noticed that the RGB inputs from
> the logic board, are connected to the three drive transistors (one for each
> color). Each input is connected to it's transistor at the center pin. But,
> on the 13 inch amplifone, the transistors have been moved to the neck board.
> It seems that the center pins of all three drive transistors are tied
> together and are all receiving the same signal.
>
> I guess the next step would be to cut some traces and route the signal in the
> same manner as the regular Amplifone board. I would sure like to know why
> Atari decided to alter the monitor design, to eliminate the RGB inputs. Why
> would they want you to have a B&W monitor with the brightness too high? It
> looks like a factory mod, since I have to of the monitor boards for the 12
> inch and they both have been modifed in the same way.
>
> Scott
Received on Mon Sep 27 03:56:51 1999