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Connecting 68k Macs to LCD Monitors


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Yep that's the Apple CD-SC. It wasn't working and the ATOM NetTop board was in need of a home, so it almost took up residence in there. I think the case is back in the project box with its bits, slated to for reassembly.

 

It looked like a Snow White Design Language Mac Mini to me at the time, so naturally, I was looking for a set of black peripherals. Couldn't find my black Belkin mini-mouse, so the tiny clear one stood in for it, the tombstone mouse is there for scale. I think the ATOMICmini has finally found a home in the ZipPlus, dunno, I've got another six months to go before that project is overdue for completion, the ATOM, not the ZipPlus . . .

. . . the MoBo I got eighteen months ago. :I

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  • 2 weeks later...
  • 2 months later...
by zuiko21 » 31 May 2012, 15:32

The monitor sense codes were very well thought, IMHO. First a bunch (0-6) of fixed resolutions, and the detected code (7) in the absence of monitor did halt video out. Then came the extended codes, read off a different method... from what would be seen by older cards as "7" (i.e., no monitor), avoiding damage to the unsupported monitor -- fixed freq. was rather common back in the day. 16" (832x642, 75 Hz) and 19" modes (1024x768, 75 Hz) were implemented this way.

 

This doesn't get enough attention. The sense code implementation is the main reason a lot of LCD monitors won't work with Compacts, even when they are nominally capable of appropriate sync rates. The Mac video chip is programmed to be adaptive, but to shut down if it doesn't recognise an acceptable static pattern on the 3 sense lines. Monitors with advanced VGA standard implementation will try to send a serial ID code over just one of those sense lines, and that can spook the Mac adapter into shutting down or sending the wrong sync signals. The monitors that work will be the ones that have VGA firmware that can detect an adapter mode that requires the deprecated passive ID sense codes, and to switch off the serial ID signal.

 

It's a mystery to me how the dip-switch adapter plugs handle this without any active electronics. They have to fool the Mac into believing the monitor has acceptable specs, and then rely on the monitor firmware to recognise the sync and adapt resolution to match. That's probably why success is a bit hit and miss.

 

Rick

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I've just found another 17" LCD that works straight up and no fuss

 

Samsung Syncmaster 740A. ($15 from recycler)

 

This is a really good unit with telescopic stand for height adjustment and good onscreen menu.

 

Whatever upscaling it did, it had no problem at all with the 66Hz sync.

 

I wonder if we should start a list somewhere (a wiki, perhaps?) where people can add to the list any LCD monitors that they have been able to connect with a basic adapter. It could save others quite a bit of time and encourage saving of such monitors.

 

[bTW - mods.. when I access the wiki pages I just see plain text with basic HTML format, no style-sheet presentation. Is there a problem with the style-sheet or forum software there??]

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It's a mystery to me how the dip-switch adapter plugs handle this without any active electronics.

Someone posted a link to a table of the sense-coding setup somewhere, there is one diode involved in the mix, however active you want to call something that simple. ;)

I'll see if i can find it. Sounds like something I'd snag for local backup. }:)

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I've got three 14" lcds (1024x768 native) that I use with my Macs. The last one I bought I paid $10 for from a pawn shop - it's a Dell. The others are an HP & a no-name. They all worked well with my Quadra 605.

 

I've found that the issue is usally with the adapter not the monitor. For the Q605 make sure you have 1 MB VRAM (two video modules installed) and it will do 1024 x 768 with no issues. Both Sys 7.5.5 & OS 8.1. If you hare having issues get a different video adapter with switches & set them for 1024x768.

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I must admit, this topic has me hugely confused!

 

I'm thinking about getting an LCD monitor for my LC475, both to take advantage of higher resolutions and against the inevitable day when my CRT packs in. The gist of this thread (from what I can make out) is that many LCD monitors don't work properly with 68k Macs, even with the appropriate Mac/VGA adapter. Is this the case?

 

I have my eye on an old Dell E151FPp monitor on ebay (1024x728 @ 75Hz native resolution). Is this likely to work, or will it require technical jiggery pokery?

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Many VGA LCDs only sync @ 60Hz, which is a problem with many Macs which don't put out a 60Hz resolution. MultiSync type LCDs work with traditional Mac resolutions/sync rates.

 

You've got me curious about your report on the Q605:

video: 512 KB VRAM, expandable to 1 MB (remove both 256K VRAM SIMMs, plug in 512K replacements; supports 512 x 384, 640 x 480, 640 x 870, 832 x 624, 1024 x 768, and 1152 x 870 resolutions. We have a field report of an 800 x 600 option as well.

Did you try running it at 800 x 600?

 

As for 1024 x 768 @ 75Hz, Macs can run this @ 60, 67 & 75 Hz rates, depending on the Mac. Some will output @ 75Hz while others won't IIRC. A lot depends upon when the Mac was introduced. VGA and Mac resolutions/sync rates developed in parallel, converging as time passed. In much of the 68k Mac history, 60Hz was considered flickery on a CRT, which isn't an issue for LCDs. By the Quadra era VGA resolutions began to be supported by Macs.

 

edit: has anyone got a link to Mac resolution/scan rate chart? The closest thing I could find online was:

http://home.earthlink.net/~gamba2/vid-mon-matrix.html (bottom of page)

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I'm using Dell 2408 24" display - best of all worlds... It can be used with Apple II!!! It has VGA, HDMI, DisplayPort, DVI-D, Component and s-video. I was very carefully choosing this display and been researching on and off for 6 months and found this one that I am happy with that I can use on ANY computers or devices. I am planning on buying Dell 2711 for my MacPro, it also has same ports as 2408 has.

Cheers

AP

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I've had great luck with my dip-less converter and an LG Flatron E2242 that I bought new several years ago as a second monitor. The converter I have is this one: https://www.amazon.com/gp/product/B0002J1JAE/

I have used this configuration with my Powerbook 540c and am able to use it at 640x480 in both mirroring mode and as a second monitor, and 800x600 as a second monitor. I can't recall if I tried it with the 540's narrower 640x400 resolution (with thousands of colors).

I have also used the same configuration with my LC III with 768KB VRAM and while I do have access to the thousands of colors I don't seem to be able to access the higher promised resolution of the added VRAM module. Still, it otherwise works great, if a little fuzzy at 640x480 interpolated.

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The Visio E221A1 21" TV which is native 1920x1080 and has VGA in has managed to sync with every resolution and frequency I've been able to get out of my 68k macs, including oddball ones like 832x624@72Hz. It's also been able to display the 800x600x95Hz video output on my iMac G3.

Edited by corgski
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Kai Kramp's collection of Macintosh related hardware hacks seems not to be available as a website, anymore. However, it can  be found somewhere in the back of intarwebs as a copy of the early standalone file to be viewed on a classic Mac. Very useful this file can be: loeten-am-mac-016.hqx. This file contains a lot of pinouts and hints like how to make a hardware handshake cable for the serial port, wire the sense pins correctly to set up a desired video resolution or also overclocking information. Some portions are written in English language, the rest is in German.

Edited by register
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8 hours ago, register said:

Kai Kramp's collection of Macintosh related hardware hacks seems not to be available as a website, anymore. However, it can  be found somewhere in the back of intarwebs as a copy of the early standalone file to be viewed on a classic Mac. Very useful this file can be: loeten-am-mac-016.hqx. This file contains a lot of pinouts and hints like how to make a hardware handshake cable for the serial port, wire the sense pins correctly to set up a desired video resolution or also overclocking information. Some portions are written in English language, the rest is in German.

A number of pages are on the Internet Archive,  here:

 

https://web.archive.org/web/*/http://lam.kilu.de/lam2//*

 

- Alex

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Hi,


What would be the least expensive LCD monitor to connect to a Mac Quadra 840 AV ?  I don't need a large monitor or a fancy one. I just want to see if the computer works and I no longer  have a CRT. I gave them all away because they took too much space!  

 

Would the Dell Ultra Sharp 17" work with the 840AV?   Here's one on eBay:

 

https://www.ebay.com/itm/Dell-UltraSharp-17-inch-Desktop-Computer-PC-LCD-Monitor-with-cables-used-good/313417448954

 

Thanks!

Edited by Alain Briot
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Hey, welcome to the site!

 

That monitor would work fine, but the 840av can do 1152x870 as its maximum resolution. That monitor should have no trouble with it but it'll look slightly weird compared to a computer outputting exactly 1280x1024. (there are graphics cards you can install that can do 1280x1024 or higher, but I don't know the state of cost on those right now.)

 

If you go for a 15-inch ultrasharp you can do 1024x768, if you prefer. (I've done off resolutions close to this on LCDs, it's usually fine.)

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