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

[ferdimh@gmx.de]

On 21 Jan., 00:06, Polymorph <polymorp...@hotmail.com> wrote:
> Hi All,
>
> If you've not been following another other thread that I started, my
> daughters IIgs monitor died just before Christmas and I've been
> attempting to repair it. Although I made it better, its still not
> perfect.
>
> Because of this I picked up a Commodore 1084s monitor off of eBay to
> use as a replacement. I have tested the monitor with a DVD player and
> the image produced was quite good, so I know the monitor is working.
> However, I wired up a cable as per the Apple II FAQ over the weekend
> and had troubles getting the monitor to synch with the RGB signal. The
> image just kept scrolling all over the place. I tested the cable, and
> everything seemed to be wired correctly.
>
> In an attempt to fix the problem, I tried:
> (i) to wire the IIgs's composite synch to the horizontal synch
> (ii) switch the monitor between 50Hz and 60Hz
>
> None of the above made any difference.
>
> One thing I should note is that just about everywhere lists the 1084
> monitors D-9 RGB connector as being female, however in the monitor I
> have it is male. Consequently, my cable has a female D-9 socket. I
> have made the assumption that the wiring would still be the same (i.e.
> pin 1 mentioned in the A2 FAQ is pin 1 on my monitor). This seems to
> be true as I do not think I would get the image that I am getting if
> it were incorrect. It just seems to not be synching with the signal.
>
> So I did some snooping around in the c.s.a2 newsgroups looking for
> threads on using 1084 monitors with the IIgs. I found a post by Jeff
> Blakeney in the mid-1990's mentioning the usage of a 75 Ohm resistor
> wired between the composite synch and ground to alter the voltage to
> more acceptable levels for the 1084 monitor. Most other posters using
> a 1084 don't mention any requirement for doing this, and the Apple II
> FAQ doesn't mention it either. But I plan on giving it a try once I
> get a chance on getting to my local electronics dealer.
>
> To gauge the likelihood of success, has anyone else had to use a 75
> Ohm resistor in this manner to get a 1084 to synch with the IIgs? Is
> there anything else I can try to get the image to synch?
>
Is the image rolling up and down or left/right?
If it is rolling up/down then you're lacking vertical sync. Otherwise
you're lacking horizontal sync.
Wiring Composite sync to Horizontal sync should give horizontal sync,
but there may or may not be vertical sync. One thing to try would be
to wire Composite sync to Horizontal AND vertical sync.
If there is no horizontal sync you either have a bad sync connection
(whereever... You didn't wire the DVD player to the DB9 input, did
you?), or the sync level is too low (AFAIK Commodore used TTL sync,
i.e. 3Vpp, but the IIgs uses only 0,7Vpp, however I'm not shure with
this.)
Does the 1084 have a switch to select analog or digital mode? If it
has it should be set to analog so that the monitor takes sync from the
composite sync input pin.

> One thing I should note is that just about everywhere lists the 1084
> monitors D-9 RGB connector as being female, however in the monitor I
> have it is male. Consequently, my cable has a female D-9 socket. I
> have made the assumption that the wiring would still be the same (i.e.
> pin 1 mentioned in the A2 FAQ is pin 1 on my monitor). This seems to
> be true as I do not think I would get the image that I am getting if
> it were incorrect. It just seems to not be synching with the signal.
You'll get that phenomenon if you just wired the sync incorrectly.
There is a trick to figure out the pinout: Use a jumper wire to join
the grounds of the Apple and the monitor. A good ground point is the
metallic part of the D-Sub connector.
Then start with the "red" signal and test every pin on the 1084 until
you get a red display. Solder it to the connector
Do the same with green (yellow display) and blue (white display).
Now take the sync pin and tap through the pins until you get a stable
display. Now turn the monitor of, and find the ground pins by
measuring the resistance to the metallic part of the D-Sub. If it is
<5 Ω, you have a ground.

----
Ferdinand