LC and my VGA monitor

[leosadvs]

hi!.. a friend have a problem with his LC, he built a MAC-VGA video adapter

but when the mac start only show this

is anything special needed to make the video work?

 

[Gil]

I think that's a monitor problem, not the computer. I've seen that a long time ago on one of the macs at my elementary school. Have you tried another computer with it to see if its isolated to the monitor?

 

[MrMacPlus]

He built it... That very well could be the problem.

 

[porter]

is anything special needed to make the video work?

Yes, you need an adapter that does the job correctly!

Macintoshes use sense codes to determine what type of monitor is connected, then it uses the appropriate frequencies.

I happily use VGA monitors with LC-II, LC-III, Performas, Quadras etc.

The trick is to decide what to pretend the monitor is. The best starting point is fooling the Mac that you have an Apple 13" Colour display.

 

[Unknown_K]

You are stuck at 640x480 or so on an LC so don't try using an adapter with higher rez or the screen will be black.

 

[register]

The LC might support resolutions the monitor does not like. VGA at 640 x 480 uses a refresh rate of 60 Hz while the Apple 640 x 480 mode refreshes at 67 Hz. Look at this older post to retrieve specific information to check wether the adapter is made properly (sense pin connection, synchronisation line etc). Just click at the "LAM" tab and find the section "Monitor & Co.".

You might also use the software "activate all resolutions" to enable any resolution the Mac video hardware supports, overwriting the sense pin settings (unfortunately this is only possible when you actually have a working screen).

 

[porter]

The LC might support resolutions the monitor does not like. VGA at 640 x 480 uses a refresh rate of 60 Hz while the Apple 640 x 480 mode refreshes at 67 Hz.

A multisync VGA monitor would laugh in your face at your doubt that it could cope with 67Hz, however it will crumble in a zig zagging heap if given 512 x 384 to work with.

 

[register]

… what leosadvs showed in the picture. It should easily be fixed with a proper sense pin setting

 

[Bunsen]

^^ porter is right

 

[register]

I missed the multisync bit. Cheers.

 

[Bunsen]

So the best hope would be to plug the Mac into an early Mac monitor, set it to 640x480, and then plug it into the VGA monitor ... ?

 

[register]

Will the resolution not change on unplugging and plugging monitor plugs with different sense pin settings, like rotating a Radius Pivot does?

 

[leosadvs]

well the problem was in fact the home made adaptor.. my friend used this: http://img115.imageshack.us/img115/2594/59315396cm9.jpg and doesn't work for him, so we found another (the same i made for my Quadra) and it worked, thanks for the info about the sense pins

 

[porter]

Will the resolution not change on unplugging and plugging monitor plugs with different sense pin settings, like rotating a Radius Pivot does?

The pivot would have to be using a custom driver. The macs normally just read the sense lines at startup.

 

[Unknown_K]

Did the pivot have a custom monitor cable?

 

[register]

The schematic diagram shown by leosadvs is wired to the sense pin code for a fixed resolution of 1024 x 768 @ 75 Hz. As the LC does not support this sense pin code, it falls back to 512 x 384 @ 60 Hz (as diagnosed by porter). To fix the adapter, cut the connection from pin 4 to pin 7 (DB 15, Mac's side) and tie the same pin 4 to ground. This will provide the sense pin code for a fixed resolution of 640 x 480 @ 67 Hz.

 

[thinkdifferent]

hi!.. a friend have a problem with his LC, he built a MAC-VGA video adapterbut when the mac start only show this

is anything special needed to make the video work?

The adapter most likely isn't working properly. Try buying one from ebay. Here's one I found: http://cgi.ebay.com/UNIVERSAL-MAC-VGA-Adapter-1-178B-NEW_W0QQitemZ300159125224QQcmdZViewItemQQptZLH_DefaultDomain_0?_trksid=p3286.m20.l1116