• Please review our updated Terms and Rules here

LC III and Non Apple Display

L

lyonadmiral

Veteran Member
Joined
Jun 3, 2009
Messages
2,431
Location
Peru, New York
Well in my saga to get a working LC III, I did piece one together from broken pieces (in the Marketplace, I am looking for a mint one) . I don't have an Apple display, but I hooked up an IBM E74 using a DB15 to VGA 15 connector. The Mac will chime up but won't display anything. Is there something I should know about this Mac that wouldn't allow the display to sync up?
 
LCIII will do 640x480 and 832x 624 (mac only mode) only I think, so you have to have an adapter that is set to that resolution (and a monitor that syncs on green) or you will get a blank screen. The VRAM you add just gives you more color depth at the same resolution.

•video: 512 KB VRAM onboard, expandable to 768 KB; supports 512 x 384, 640 x 480, 640 x 870, and 832 x 624 resolutions
◦512 x 384: 16-bit @ 512 KB
◦640 x 400: 16-bit @ 512 KB
◦640 x 480: 8-bit @ 512 KB, 16-bit @ 768 KB
◦640 x 870 (portrait): 4-bit @ 512 KB, 8-bit @ 768 KB
◦832 x 624: 8-bit @ 512 KB, 16-bit @ 768 KB
•VRAM: accepts one 256 KB 100ns VRAM SIMM to upgrade VRAM to 768 KB total, other specs unknown, VRAM SIMM appears to be specific to
 
On that monitor adapter, are there any jumpers to be set or is it straight plug-in? I have a straight plug-in type that I have never used since I never could positively ID it. Also I have a silver adapter with jumpers on it that need to be set up right depending on the computer and monitor being used.

It might be that adapter, as well, check on that (my first impression).

Nathan
 
NathanAllan said:
On that monitor adapter, are there any jumpers to be set or is it straight plug-in? I have a straight plug-in type that I have never used since I never could positively ID it. Also I have a silver adapter with jumpers on it that need to be set up right depending on the computer and monitor being used.

It might be that adapter, as well, check on that (my first impression).

Nathan
Click to expand...

I have a straight through adapter which would explain it.
 
There are pins connected in different patterns to signal the Mac as to what video mode/resolution the monitor would support. The Mac would then switch to the proper video mode for the monitor.

Back in the day there was an adapter that had a bunch of DIP switches on it. It could be used with any Mac of the era to connect to a VGA/Multisyncy monitor. The DIP switches would allow for different jumper settings on the DB-15 port which signaled the Mac as to what resolution the screen would support.
 
channelmaniac said:
There are pins connected in different patterns to signal the Mac as to what video mode/resolution the monitor would support. The Mac would then switch to the proper video mode for the monitor.

Back in the day there was an adapter that had a bunch of DIP switches on it. It could be used with any Mac of the era to connect to a VGA/Multisyncy monitor. The DIP switches would allow for different jumper settings on the DB-15 port which signaled the Mac as to what resolution the screen would support.
Click to expand...

Are those things still available? What would I do a search for?
 
My original LC (not II or III) works just fine with a standard PC VGA monitor using a Mac-to-VGA adapter, however I had to fiddle around with the adapter's DIP switch settings to find a configuration that worked, and I believe I was only able to get 512x384 video. Maybe with more experimentation I can find a setting that will give me 640x480.
 
Macs of this vintage used a signal that differed slightly from VGA. They had composite sync and scanned at 35Khz instead of 31Khz. VGA monitors will often work (including many new LCD displays suprisingly), but you would have to look at their specs.
 
I seem to recall that some Macs of similar vintage would give you a blank screen if they had a dead PRAM battery, too. Not sure whether that applies to an LCIII.

Also, Apple made a small, switchless Mac-to-VGA adapter that plugged straight through, and would intelligently adapt the resolution based on the monitor’s sense signals. I believe it had a microcontroller or similar in it; in any case, they tend to be expensive. Their cases were the usual Apple “platinum” in colour, and they are easily distinguished by the Apple logo moulded into the plastic. I used to own one; not sure if I still have it around anywhere.
 
I have two LC IIIs, both in excellent condition - was just using one actually. PM me if you're interested with an offer - I dunno if I'll decide to get rid of one - depends on the offer.
 
I have two of the non-switchable ones, and for the record, they refuse to do anything but 640x480 but work well. Infuriated me when I tried to get 1920x1200 out of one though, heh.
 
You must log in or register to reply here.
Back
Top