[Coco] Magnavox 8CM515 / Commodore 1084 monitor

[Gene Heskett]

On Monday 12 December 2005 07:24, Rogelio Perea wrote:
>Sometime ago I got a Commodore 1084 monitor for my CoCo 3 setup. As
> far as I know this is the same monitor as the Magnavox 8CM515,
> correct me if I am wrong on this assumption.
>
Somewhat.  There were about 5 different variations on a theme, all in 
the video input circuitry (various connector styles and some had a 
whole rank of mode switches rather than just 2), and in the audio, 
since the 1084s had 2 amps & a speaker on each side for what some may 
have euphamisticly called stereo.

>This by far works better than the CM-8, except for a minor glitch on
> the composite side of the operation... for some reason the
> brightness level of the display is really different between the two
> modes: RGB-TTL and Composite, the later being the lower one. A
> friend of mine had a Magnavox 8CM515 back then and I do not remember
> having this problem, we could switch between the two modes with no
> other difference than the definition of the image on screen, right
> now I have an OK display with the RGB input but brightness goes down
> on composite, have to adjust the front bright knob to compensate up
> when going composite and then adjust down when going back to RGB -
> on RGB  the brightness control is uauslly set half way so I'd say
> the CRT is still very well in its useful life.
>
>Lacking the service manual of the 1084 it seems to me that the
> problem must be some internal adjustment in the monitor PC board tha
> affects only the composite input... any ideas of where should I
> start looking for in order to fix this minor problem?

There is a service manual in the Sams publications, but it sells for 
more than you paid for the monitor on ebay. :(

It also fails as a universal manual because it doesn't cover anywhere 
near all the variations that were made.

Major parts such as the crt and scan transformers are long since out of 
stock at NAP down in KY.  An 8CM515 is not even in the parts depts 
archive as a model they once made, so my bad scan transformer means 
its all junk, and the tube was fine when it blew up.  There used to be 
an California outfit whose name I cannot recall, but had parts for all 
that stuff 10 years back up the log.  Possibly a google search might 
turn them up?

>Thanks!
>
>--
>
>
>-=[ Rogelio ]=-

-- 
Cheers, Gene
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