• Please review our updated Terms and Rules here

Macintosh LC video output to modern monitor?

ajaxermd

New Member
Joined
Aug 30, 2020
Messages
1
Just get a super clean Macintosh LC and after recapping the power supply it seems to be working. Retrobrighted it today. Start up chime works great and I can even hear the SCSI drive spinning up.

Problem: Is it possible to output from the LC to a modern LCD monitor? I have the DB-15 to VGA adapter. The monitor detects something and says the resolution was 640x350 (or something close to that).

I have the hardware for this, but this seems to be a resolution or refresh rate issue.

Appreciate any thoughts on this one. I'd rather not buy a LC monitor.
 

HoJoPo

Veteran Member
Joined
Feb 4, 2012
Messages
862
Location
Northern Nevada
Does your DB15 to DE15 adapter have dip switches to set the monitor ID? If it does, you should be able to pick a more compatible resolution / refresh rate. If not, it may be coded in the adapter, you might want to find one that has the dip switches.
 

Timo W.

Veteran Member
Joined
Nov 25, 2014
Messages
2,103
Location
Germany
The LC came with only 256kb VRAM and can only do 512×384 and 640×480. Make sure your adapter is set to 640×480.
 

GiGaBiTe

Veteran Member
Joined
Apr 30, 2015
Messages
3,318
Location
Austin, Texas
The LC came with only 256kb VRAM and can only do 512×384 and 640×480. Make sure your adapter is set to 640×480.

Both the Macintosh LC and LC II require 512kb of video memory via adding a proprietary 256kb 68 pin VRAM SIMM to do 640x480. The LC III has 512kb on board and can do 640x480 natively. With an additional 256kb VRAM SIMM, it'll bump it up to 786kb and be able to run at a weird 832x624 @ 8bpp resolution.

A stock LC and LC II can only run at 512x384 @ 8bpp and most modern LCD monitors refuse to run at that resolution. No passive adapter will fix this problem, OP needs a video memory upgrade.

Here's the module required:
https://www.ebay.com/itm/131852599696
 

bladamson

Veteran Member
Joined
Nov 11, 2018
Messages
985
Location
Appalachia
It will probably also only do 16 colors in 640x480 with the stock amount of vram, if I recall correctly, although I may be wrong. My LC was an LCII (the vram was upgradable iirc, not sure about original LC), and I haven't had it for at least 15 years.
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
6,733
Location
Upper Triassic
It will probably also only do 16 colors in 640x480 with the stock amount of vram, if I recall correctly, although I may be wrong. My LC was an LCII (the vram was upgradable iirc, not sure about original LC), and I haven't had it for at least 15 years.

It should be able to do 640x480x4bpp with the stock amount of VRAM, yes, although the DB-15 adapter will need to be set up correctly to signal this resolution. (The LCs use a subset of the standard Mac sense line arrangement.) There is one gotchya that might still pose an issue: I believe the original LC only does 640x480@67hz; later LCs could do a VGA-compatible 60hz but pretty sure the LC doesn't. LCD monitors can be iffy about accepting non-VESA refresh rates. (You'll often have more luck with an older one.)
 

Timo W.

Veteran Member
Joined
Nov 25, 2014
Messages
2,103
Location
Germany
Yes, it will do 640x480 with 16 colors using the stock 256kb of VRAM. Mind you, I have an LC standing next to me.
 

VERAULT

Veteran Member
Joined
Jan 30, 2012
Messages
7,945
Location
Connecticut, USA
Both the Macintosh LC and LC II require 512kb of video memory via adding a proprietary 256kb 68 pin VRAM SIMM to do 640x480. The LC III has 512kb on board and can do 640x480 natively. With an additional 256kb VRAM SIMM, it'll bump it up to 786kb and be able to run at a weird 832x624 @ 8bpp resolution.

A stock LC and LC II can only run at 512x384 @ 8bpp and most modern LCD monitors refuse to run at that resolution. No passive adapter will fix this problem, OP needs a video memory upgrade.

Here's the module required:
https://www.ebay.com/itm/131852599696

He is absolutely right. I have a stack of LC's, LCII's, and LC III's. The Size of the VRAM module dictates your max resolution and color depth. You should be able to do 512x384 and 640 x 480 to a standard 4:3 monitor with db 15 adapter. I did just this morning: 20200831_202647.jpg
 
Last edited:

bladamson

Veteran Member
Joined
Nov 11, 2018
Messages
985
Location
Appalachia
Nah, afaik all the macs are non-interlaced. Not sure what the refresh rate is on the 512x384 mode, but it ought to up up around 30KHz somewhere.
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
6,733
Location
Upper Triassic
Nah, afaik all the macs are non-interlaced. Not sure what the refresh rate is on the 512x384 mode, but it ought to up up around 30KHz somewhere.

I think it’s closer to 24khz, higher than EGA but plenty enough lower than VGA to be well below the floor where any but old multisync monitors will sync with, but I don’t recall exactly. (VGA is 31.5)
 

bladamson

Veteran Member
Joined
Nov 11, 2018
Messages
985
Location
Appalachia
I think it’s closer to 24khz, higher than EGA but plenty enough lower than VGA to be well below the floor where any but old multisync monitors will sync with, but I don’t recall exactly. (VGA is 31.5)

Oh for sure, I never got my LCII to do 512x384x8 on a VGA monitor, only 640x480x4. I'm 99% sure you have to have the Apple monitor for the 512x384 mode.
 

GiGaBiTe

Veteran Member
Joined
Apr 30, 2015
Messages
3,318
Location
Austin, Texas
Oh for sure, I never got my LCII to do 512x384x8 on a VGA monitor, only 640x480x4. I'm 99% sure you have to have the Apple monitor for the 512x384 mode.

You don't need an Apple monitor, you just need one of the special adapters with dip switches to fake the Mac into thinking an Apple monitor is installed.

https://www.amazon.com/Adapter-DB15-Male-Female-Switches/dp/B0016OC1J2

I have a Belkin one with a rotary switch and I can get my LC III to run at 640x480 or 832x624 on a PC monitor. The latter resolution only works on CRTs though. 512x384 is an option on the above adapter.
 

Timo W.

Veteran Member
Joined
Nov 25, 2014
Messages
2,103
Location
Germany
His point was that an ordinary VGA monitor can not sync to the signal the Mac outputs in 512x384 mode, as it is below 31 kHz. The adapter won't change that - it only sets some ID pins so the Mac knows what resolution to use. With these adapters, you should always use resolutions that exist in the (S)VGA standard as well, otherwise all you may get is a black screen.
 

dr.zeissler

Experienced Member
Joined
Jan 4, 2014
Messages
417
Location
Germany

I am trying to set my LC to 512x384 on TFT for a long time...it simply does not work. Same with the LCII. It works on LC475 just fine.
What is the problem with the LC. I would love to set the LC to 512x384 in order to test the native hardcoded apps that a re actually not working correct or not working at all in 640x480.

That is the machine:

Doc
 

vwestlife

Veteran Member
Joined
May 2, 2008
Messages
5,371
Location
central NJ
The Mac LC's 512x384 mode is 60 Hz vertical (same as VGA), but only 24.48 kHz horizontal, too low for many LCD monitors.
 

dr.zeissler

Experienced Member
Joined
Jan 4, 2014
Messages
417
Location
Germany
I know, I rechecked this again. It's about 24.5Khz/60hz as you said.

I have about 10 different DB15/VGA Adapters. I checked all switchable before. Now I checked three that are not switchable.

1. Output 640x480 works with nearly all TFT's I have
2. Output 640x480 works with only some of my TFT's
3. Output perhaps? 512x384 works with none of my TFT's
3.a. => no picture at all with or without error message
3.b. => switches the TFT to 720x400 only a white screen nothing else
3.c. => switches the TFT to 640x400 only a white screen nothing else

I have one adapter that is switchable and this works on LC475 with Nec 71vm, but that is a very fast machine and it also does not support system6 with single-finder, so no real solution for me. I think about buying a high-resoultion-nubus-card for my Mac II. The high-resolution-card also supports very low resolution that the "normal" Toby card can not. But these cards are very hard to find.
 

Timo W.

Veteran Member
Joined
Nov 25, 2014
Messages
2,103
Location
Germany
As I have written earlier:
His point was that an ordinary VGA monitor can not sync to the signal the Mac outputs in 512x384 mode, as it is below 31 kHz. The adapter won't change that - it only sets some ID pins so the Mac knows what resolution to use. With these adapters, you should always use resolutions that exist in the (S)VGA standard as well, otherwise all you may get is a black screen.
The adapter does not do any conversion. The dip switches tell the Mac what resolution to use. If your TFT does not sync to 24 kHz, you won't ever get a picture from the LC at 512x384.
 
Top