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Re: Problem Using a Commodore 1084s Monitor on a IIgs

 To: Michael J. Mahon
Michael J. Mahon wrote:

Never worry about this.  If the store is concerned about their
transaction costs (which are almost certainly a few tens of cents)
then they should just give your the part!  (And some will if they
know you.  ;-)


OK, but it still feels kinda weird.


The 200 Ohm pot will provide you with complete adjustment flexibility,
corresponding to *all* values of resistor, so you don't need another
fixed resistor for this.


OK, I'll stick with just the 200 Ohm pot then.


Specifying a video peak-to-peak level of 0.7v and a sync peak-to-peak
level of 0.3v corresponds to the standard composite video+sync level
of 1v (of which 0.7v is video going positive from black level and 0.3v
is sync going negative from black level).

It would not be unusual for the internals of the monitor to accept
composite sync at the same level and polarity at which it would be
found in a composite video signal.


Right, that makes sense to me.
I don't have this system connected at this time, sorry. However using the 200 ohm pot as was suggested here should do the trick for you. 
 >>
No worries. Its good to hear of someone who experienced a similar problem as myself using the 1084S with the IIgs. I wonder why most people don't have a problem? Did later revisions of the 1084 line come with greater tolerance to sync levels? It has me stumped how come some 1084 monitors require modification of the sync signal and others don't. 

The sync level tolerance is strongly dependent on the input circuitry
of the monitor, and a very minor change would make it quite insensitive
to sync level.  It would not be surprising if this were the case in
some of the monitors (which may have different manufacturers).
I'm just surprised that I have had to drop the sync level to such a low value though when others have not. I mean its gone from ~3.87V to ~0.56V, and it seems that it is still too high! This seems like a pretty big difference. I'm still amazed that later revisions of the 1084 can handle the IIgs' comp sync signal unmodified. It would be interesting to know what they changed to allow for this to be possible (as I'm sure they didn't have the IIgs in mind when making the 1084 monitors ;-). 

Cheers,
Mike
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