Re: Need Help Adjusting IIgs AppleColor RGB

[Michael J. Mahon <mjmahon@aol.com>]

D Finnigan <dog_cow@macgui.com> wrote:
> Kevin Dady wrote:
>> 
>> are you positive the transistor is inserted correctly?
>> 
> 
> Fairly certain: the flat part of the transistor is facing up, and the
> emitter and base legs are matching as shown on the board.
> 
> I recall someone mentioning that when I replaced the transistor, the colors
> would need to be adjusted. Presumably this would be because of the new
> transistor having better specifications than its predecessor and brothers.

..or just slightly different characteristics, which would be expected even
for an exact replacement. 

There is a prescribed order for making color adjustments, to ensure that
the process converges. It would be best to find the service docs for this
monitor for the procedure, or, failing that, review service docs for a
comparable (in schematic) monitor or TV. 

What you have so far described could also result from either an improper
replacement or additional failures in the circuit. 

If I were troubleshooting this monitor, I'd start with comparing voltages
under black screen conditions for equivalent points in the three color
channels. Big differences would be suspect, and could point to the cause. 

Next, DC signal injection at the inputs together with more comparable
voltage measurements. 

The "screen", or DC, adjustments for two colors should be used to get a
neutral gray background if the brightness is turned up a bit 
The channel gain controls should be set to get a neutral white on a
monochrome pattern, like text. 

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon