Most older Apple displays used a DA-15 connector, rather than the DE-15 connector commonly used on PCs. This included the original iMac line, at least up to the iMac DV (not sure about the DV itself). They were not directly pin-compatible with VGA displays, either. Apple briefly had displays with standard DE-15 connectors on the CRT Studio Display units, but would switch to DVI and ADC shortly thereafter.

Depending on the model, getting it to digest a standard VGA-type signal may be more trouble than it's worth.

I would be more interested in using the old IIGS color 12” as a 15khz RGB display but I could never get it to “turn on” after adapting

The eMac also had a proprietary VGA connector that you could hack onto a normal VGA cable.

As for the DV iMacs, it's not possible to use it as an external CRT monitor (I happen to have a iMac DV 400 as well, I'm definitely not going to try and modify it as a CRT monitor)

Why can't iMac monitors be used as displays for PCs? I'm still not clear on this.
They're not VGA?

Not directly; most use a different connector. It may be possible to find or assemble an adaptor that would get this to work, but it may not be trivial. As mentioned, some Apple monitors remain in a low-power state until a particular signal is received. They also used to use various tricks to detect screen model/size and supported display modes.

640K!enough wrote:

Most older Apple displays used a DA-15 connector, rather than the DE-15 connector commonly used on PCs. This included the original iMac line, at least up to the iMac DV (not sure about the DV itself). They were not directly pin-compatible with VGA displays, either. Apple briefly had displays with standard DE-15 connectors on the CRT Studio Display units, but would switch to DVI and ADC shortly thereafter.

Depending on the model, getting it to digest a standard VGA-type signal may be more trouble than it's worth.

That's not correct - Apple's DB15 monitor pinout is compatible with VGA - you can get "reverse" adapters to VGA; I'm able to use a 17" ColourSync AV monitor on a PC without issue. iMacs from the DV line up had a hidden VGA port at the back of the casing, which allowed you to plug in another monitor as a mirrored display. If they're not compatible, why can you get DB15 to VGA adapters which many Mac users used over the years?

Older Apple monitors used for desktop machines - eg. Apple 13/14/16" branded monitors mostly require sync on green support, which may be lacking in many VGA graphics cards.

Monitors used in compact Macs are not easily converted, without significant hardware hacking.

JB

Byrd wrote:

That's not correct - Apple's DB15 monitor pinout is compatible with VGA - you can get "reverse" adapters to VGA; I'm able to use a 17" ColourSync AV monitor on a PC without issue. iMacs from the DV line up had a hidden VGA port at the back of the casing, which allowed you to plug in another monitor as a mirrored display. If they're not compatible, why can you get DB15 to VGA adapters which many Mac users used over the years?

I said that they are not directly pin-compatible. This should be obvious, since the connectors used are quite different; DA-15 on the Macintosh for most of its history (until the late 1990s or so) and DE-15 on the PC. The connectors are obviously not interchangeable; they are not the same size, don't have the same number of rows of pins, and the pins are in a different order. In most cases, the signals are compatible, but you still need the adaptor to re-order the pins and take care of the sense signals (and possibly other Apple-specific details).

Apple even made at least one display that used the same DA-15 connector, but was not pin-compatible; that designed for the Apple IIGS.

Hamby wrote:

The question then occurred to me; what about other Mac displays? Could a classic Mac CRT be used as a replacement for a Compaq portable's built-in monitor, or vice versa?
I'd be loathe to sacrifice one vintage, historically valuable computer to repair another, but if it was otherwise dead, anyway...

Is this something that should be dead obvious, or completely unworkable?

Most small mono CRTs have the same pinout and similar enough specs that they are interchangeable. Back in the day I pulled the green CRT from a Compaq Portable and put it in a Mac Plus that had broken CRT. I may have had to the only Mac Plus with a green screen. However, that was literally just swapping the CRT itself, it was still being driven by the original board in the Mac.

Most later Mac CRT monitors - say PPC era or later will work on a VGA PC. The earlier models from the 68k era were often fixed frequency and won't do VGA. I tried adapting one of the 13" Trinitrons, but couldn't get it to sync.

The internal 10" trinitron in the color classic can be modified to do 31.5kHz 640 x 480 VGA - This is often done when upgrading the Color Classic as it isn't as hard on the monitor as using the standard Mac 640 x 480 mode at 35kHz.

Vynix wrote:

The eMac also had a proprietary VGA connector that you could hack onto a normal VGA cable.

As for the DV iMacs, it's not possible to use it as an external CRT monitor (I happen to have a iMac DV 400 as well, I'm definitely not going to try and modify it as a CRT monitor)

Not so sure about that. VGA is nothing more than analog RGB with separate Hsync and Vsync. That is definitely used in all iMacs internally, regardless of connector.

Now, I'm not sure someone has successfully done this mod, but a few people started back in 2014:
https://www.tonymacx86.com/threads/imac-g3-sl … nnector.125515/

They failed because of the I2C IVAD issue, and that only. That I2C issue was solved a few weeks later for the eMac:
https://en.wikibooks.org/wiki/How_to_modify_a … xternal_monitor

So if you were to combine these two approaches it should be possible to get any iMac working as external VGA monitor. It's just that nobody seems to have done that yet...

could always turn it into an aquarium

oeuvre wrote:

could always turn it into an aquarium

And then that wonderfully beautiful monitor goes to waste...

I've got the slate (?) iMac, and I've got a non-functioning Snowball iMac in the closet, which is part of the reason I'm asking about this.
I hope the only problem with the closeted iMac is the HD and the battery, but if it can't be salvaged I'd love to use the beautiful CRT with another computer.

I once saw a video of a guy showing to repurpose an iMac to a cat's sleep box/lookout.
Cute!

Why don't you just spend $1+shipping to buy another iMac for replacing the screen?

There are official Apple VGA adapters that allow one to use a Mac monitor on any standard VGA device. Post 1994ish Apple branded monitors are all multisync and support H+V sync and will work with any PC. Anything earlier is likely to be fixed frequency and/or expecting composite sync or sync-on-green.