High Resolution Display video card not working with 12 inch colour monitor?

[cesare]

Hi, just wondering if you knowledgable lot have come across this before.

I've just picked up another IIcx (i've got a bit of an old Mac problem at the moment), which came with a High Resolution Display card. The machine had the usual dodgy capacitors, dodgy PSU, a dodgy speaker, and a dodgy floppy drive, but amazingly no damage to the motherboard. So, a bit of cleanup work and new caps, and it's now happily running. Plugged into an apple 13 inch monitor, it produces a nice 640*480 output - I actually recapped the video card as it had some ghosting before. However, if i plug it into an apple 12 inch colour monitor (from an LC) it clearly doesn't get the sync right, and produces a dodgy 'wrong sync' type image.

Now my understanding is that these cards do support the 512 x 384 displays, so i'm a bit confused. Were there different revisions? Is this actually telling me that there is a problem with the monitor detection on the card? If not, what else is going on here?

The lead on the 12 inch monitor is captive, so i'm guessing this is correct, and it produces a lovely image on an LC (which also produces a lovely image on the 13 inch monitor, so I know that at least one machine can work out what it's connected to).

Any ideas or help appreciated!

Images of the card in question attached:

 

[beachycove]

Is this relevant?

myoldmac.net - Macintosh II Video Card (M0211 and M5640) - Buy it

Here you will find those rare and vintage computer items you have been looking for.

myoldmac.net

 

[cesare]

I think this indicates what I was suggesting, which is this should work on this monitor. I think i'll investigate the resistor side of things and trace how it determines which monitor is connected in case this is what is failing. As i mentioned, the capacitors on the card were shot, so it's had a tough life, or more realistically, has had a tough time in a hot loft for some of it's life...

 

[Juror22]

I don't believe this card outputs to the 12" Macintosh Display as shown in this matrix link
I'm also pretty sure that I tried to do this at one time (because I thought that the small monitor size would be handy for testing things out), but when I found it was incompatible with a variety of things I moved to using the 13" High Res Monitor because they worked with so much more and still had a relatively compact size for a CRT.

I don't have my 12" monitor anymore, or I would try to confirm this for you using my card and IIcx.

 

[cesare]

I've tracked down an original apple press release for it here - https://web.archive.org/web/20101205230251/http://support.apple.com/kb/TA40070

This mentions support for the 12 inch displays, unlike the above matrix you have linked. This suggests that the 'default' is the lower res. I was happy to give up thinking the site I read that mentioned this support was incorrect, but i'd be surprised if Apple don't know the capabilities, especially as they specifically mention that 3rd party cables may trip this monitor up.

 

[Arbee]

We emulate that card in MAME and didn't see any hint of support for anything other than 640x480.

 

[cesare]

Yeah, I think you are right.

Sticking a scope on the horizontal sync gives me 32khz or so, which is more like 640*480 60Hz, so I wonder if this card 'defaults' to a VGA type output, rather than 66Hz. The apple doc does appear to be wrong.

Either way, it looks like it is 640*480 only, so there is some mis-information on the web. This makes sense. Given the built in video on the IIci supported the 12 inch displays, there wasn't going to be much of a market for selling new video cards to the earlier machines to support a worse display than they were previously using.

 

[opualuan]

If you really want that combo to work…

640x480 mod for 12” display.

Mobley's Message->Computer->Modification03 (E)

Talk about SUBARU LEGACY (BF5), JAZZ, Macintosh (LC) and etc.

mobley.jp

 

[EIMS]

I've tracked down an original apple press release for it here - https://web.archive.org/web/20101205230251/http://support.apple.com/kb/TA40070

This mentions support for the 12 inch displays, unlike the above matrix you have linked. This suggests that the 'default' is the lower res. I was happy to give up thinking the site I read that mentioned this support was incorrect, but i'd be surprised if Apple don't know the capabilities, especially as they specifically mention that 3rd party cables may trip this monitor up.

I think I might be able to shed some light on this. I think the "12- and 13-inch Monitor Timing" that press release is referring to is the 640x480@67Hz mode, which is supported by Apple 12" monochrome monitors. The "512 by 384 pixel (default mode)" is listed under "RGB interlaced video resolutions", which are when the card is in NTSC timing mode. 512x384 will be an under-scanned NTSC mode, where 640x480 is over-scanned. That is also why the card can switch between 512x384 and 640x480 in NTSC mode, that is just adjusting the area of the screen used, not the timing.

For some technical details, the card has the same two timing oscillators as the older Macintosh II Video Card. 30.24 MHz is for 640x480@67Hz, and 12.2727 MHz is for the NTSC mode (I think that dot clock frequency gives square pixels for NTSC timing). The 12" RGB monitor is typically run with a dot clock of 15.6672 MHz, which this card has no way to generate.

The IIci on the other hand has 3 timing oscillators next to the RBV chip. 30.24 MHz for 640x480@67, 57.2832 MHz for the portrait display, and 31.3344 MHz, which can be divided by 2 to get 15.6672 MHz for the 12" RGB.

512x384 video timing for the 12" RGB is on page 13 of the Mac IIvx developer note

 

[cesare]

That's an interesting read, thanks for posting that.