View Full Version : Built a VGA cable for my LC

February 12th, 2012, 05:54 AM
Hey guys!

This this Friday I thought about taking my LC out and put it into use. Sadly I didn't have a Macintosh Video DB15 to VGA HD15 adapter laying around. So I thought that since I was going to hook it up to a KVM anyway, I could just as well just build a nice cable/adapter.
It's all pretty straight forward if you have an LC with expanded VRAM (without the extra VRAM there is no 640x480 mode to please the VGA monitor). Easy!, or so I thought, in the process I did make a lot of mistakes, so it all took much longer than it should have done. I did document everything with my camera, even the failures. So here's my Saturday project, hopefully someone will enjoy it.
(I could only attach 5 images so check my flickr (http://www.flickr.com/photos/oneplusfifty/sets/72157629277048685/) to see the whole set).

The theory behind it all
The Macintosh LC have a DB15 female monitor port. Out of this we can get RGB analog video along with Horizontal and Vertical sync, this happened to be something which we can feed into a VGA monitor! The RGB and Sync is all we need for the VGA monitor to be happy.
However!, on the Macintosh side of things there are "sense"-lines. These consist of three pins/lines by which the monitor is identified, different monitors have different SENSE-codes. If a line is grounded, it's a 1, if it's floating it's a 0, and the way to wire them up is in the pin-outs of the adapter I used as a guide.
(I don't know if the LC supports the extended sense codes?, those requires diodes to be used.)

The pin-out for the adapter and the list of SENSE-codes are from pinouts.ru (http://pinouts.ru/VideoCables/MacVideoToVGA_pinout.shtml), and the Mac to VGA adapter page.

Added: It might not be clear from the wiring diagram, but the only signals actually coming out from the Macintosh Video port to the VGA monitor is: Red, Green and Blue, along with Horizontal and Vertical Sync, nothing else!, no logic, no nothing.
By setting the SENSE-code to that of a 13" AppleColor Hi-Res RGB monitor, we are telling the video adapter that we want: 640 x 480 at 66.7 Hz and 35.0 kHz. That's all :) If your multisync monitor supports those operating frequencies, we can use that as our LC's monitor.

On with the construction!
When I striped one end of the VGA cable I saw that the shielding around the analog signal wires were just foil, with a thin threaded wire (which I could solder!) wrapped along the insulator of the signal wire, inside the foil wrapping.
I was worried that this might cause problems with different grounds shorting out, so I checked the cable and found that they were all connected to each others. Even the outer shield for the entire cable!, however this is still alright for my use because the pin out for the adapter says to tie all the grounds to each others.

Pretinning the wires and checking which is which. I found that my cable didn't have a wire for ID0, so I couldn't connect that on the DB15 end. I found the SDA and SCL for the I2C and the +5V for signal reference voltage (I think?) and heat shrunk them neatly together so they wouldn't short anything.

Done with soldering it all together, was eager to check if it would work. It didn't!
My LC doesn't have a NVRAM battery, I thought it might not start at all. I checked this at the Internet and found an advice to start the LC, let it run for a moment and then turn it off and on again quickly, which should make it start anyway. A Bing but no picture, bummer.

Maybe something is shorted?, nothing. However I did find that I haven't wired all the grounds together (which the wiring diagram says to do), I soldered them together, and tested again. Nothing.

Then I thought that the diode I used to get the extended SENSE-code might be the problem (if the LC doesn't support those). So I removed the diode and grounded pin 7 and 10 (this the id for a 13" Apple Color monitor, with a 640x480 resolution). Still no picture.

Then I checked the wiring again, it was correct. I checked my listed pin-out for the VGA cable, aha! I found that I had wired H-sync and V-sync the other way around, no wonder I got no picture! Fixed that, and tested again... no picture.

I remembered that I some year earlier had tried to solder in jumpers directly on the LC motherboard, to try and make an newer Apple Monitor to work with it. That didn't work out at all, so I checked the motherboard, no jumpers left and out of desperation I decided to re-solder the connections anyway to be sure. Tested again, no picture.

Confused and tired, having worked on this cable for way to long, I checked every single pin again. Then I found it, not only had I switched the H- & V-sync cables, I'd also switched the V-sync and Sync-GND! That should fix it. Tested it again, no picture...

At this point I did let the LC run for a little, looked for breaks on the connector, maybe I'd broken wires off while doing all the soldering and testing, and then I saw a tiny single strand of wire between V-sync and Sync-GND, removed that and...

I finally had a picture! The LC was still alive and I could now start using it again. Phew, that was such a pleasing sight, the black cursor on the checker background, how I've missed that!

(Now you might notice there's no [?] diskette or booting happening, it's because the SCSI drive doesn't contain a bootable Mac System. I removed it's power to check if I got the beautiful [?] diskette, I did, and I was happy!).

February 12th, 2012, 12:51 PM
Well done!

February 12th, 2012, 12:57 PM
Ah yes, I've had those ten-minute jobs that took a day... Congratulations!

February 13th, 2012, 08:35 AM
Thanks guys!, today I'm in the process of working out the hard drive, it had it's jumpers set to ID 6 (not ID 0 that the LC uses), changed that but still no boot. It also seems that my other SCSI drive doesn't contain a bootable System... it seems like I'm starting a tradition here! Luckily my little brother has a portable Macintosh so I can write new Macintosh System 6.0.8 (oh, yeah!) install diskettes. Hopefully that will work out alright :)

Anyway, is this the right place to post Macintosh 68k related build-logs?, I saw that there were blogs here as well.

February 13th, 2012, 03:06 PM
A little update on the LC. I think it's going to become a tradition, the fan have started to act up, so that needs to be replaced.
The good news: I got my install diskettes, and I might have a fan that fits :)

Maybe I should rename this thread to ajcc's LC adventures and fails? :P

February 13th, 2012, 06:28 PM
From what I remember the fan is just your standard 12v fan, 60mm? with a 2 pin connection

February 14th, 2012, 02:52 AM
From what I remember the fan is just your standard 12v fan, 60mm? with a 2 pin connection

You're right! 60x60x15mm, 12V 0.1A.
It doesn't have a removable connector, the two wires + & - are soldered directly onto a special connector in the plastic fan/speaker-frame.

February 14th, 2012, 04:30 AM
Now the LC is somewhat happy again :),
so now I can get back to fighting the evil SCSI devices.

This time the 5 minute project actually was a 5 minute project.

New and old fan, side by side. They are both 60x60x15mm and 12V, although the new one consumes less power.

Checking that the fan actually works!, it does.

Zero budget soldering jig, it's a thing.

Heat shrunk and happy, even color matched to the LC end.

Spinning away inside the LC.

(I think this replacement fan might be from my SPARCstation IPC I had several years ago, I remember that I saved the fan and speaker. Unfortunately I threw most of the SPARC away :( )

February 14th, 2012, 05:12 AM
Fighting the evil SCSI
At least the LC now let's you boot from a diskette with a SCSI hard drive installed in the system. I did set the new hard drive to ID 0, active termination and tried the default "Target Initiated Synchronous Negotiation is disabled, and then the Initiator is required to start a negotiation handshake if Synchronous SCSI transfers are desired.", both as disabled and on, same thing for both.

All I get is this:

When I try to run Apple HD SC from the Macintosh System 6.0.8 System Install diskette (1.4MB version). IIRC this is the application you run to prepare a SCSI drive for the System installation?

The "new" hard drive, comes from an old IBM PowerPC system we had at a school computer club, never got that system to work before the school threw us out. But I got it's hard drive though :) I have installed Macintosh System 7 on this drive before, and also used it on PCs, so it should work.

Update: As you all can see, it's not an Apple branded hard drive, and apparently Apple HD SC doesn't like those (evil fruits and friendly SCSI?).

Update: I found a guide on how to patch HD SC 7.3.5 (http://www.euronet.nl/users/ernstoud/patch.html) to use almost any SCSI drive, and it worked great! The links are broken, but all the files are on Apple's Old Software page (http://www.info.apple.com/support/oldersoftwarelist.html). I placed the patched version on the 6.0.8 diskette, and ran it from there.
So now I'm currently in the process of installing 6.0.8 onto the new hard drive inside the LC.

How happy this makes me! :D

February 14th, 2012, 07:20 AM
Yay!, a grey Macintosh System 6.0.8 desktop on the LC! :)

February 14th, 2012, 09:25 AM
Yay!, a grey Macintosh System 6.0.8 desktop on the LC! :)

Nicely done!!

I always hated all the headaches required to get NON-Apple ROM drives going (either patched HDSC Setup, or use 3rd party utils).

February 14th, 2012, 09:38 AM
Nicely done!!

I always hated all the headaches required to get NON-Apple ROM drives going (either patched HDSC Setup, or use 3rd party utils).

He he, yeah, I had no idea this was the case. A lot of unnecessary checking, testing and head scratching. But, I did learn something new!, and I was lucky enough to have another computer with PC Exchange on it.

February 14th, 2012, 09:45 AM
So my LC had 4MB of ram, in total with the 2MB from the board included. I had this pile of ram-sticks:

Hopefully I've broken the tradition and get to keep this:

Yep, maxed out RAM!
I should really test the RAM though, I might still be unlucky with these things.

February 15th, 2012, 11:06 AM
Next step is to recap that LC motherboard. :)

There's a pretty rare upgrade for the LC called a Presto Plus. It upgrades the CPU to a 68040, adds an ethernet port, and does some nifty ROM patching magic to add 32MBs of RAM. I've yet to find one. Some day I will, though.

February 16th, 2012, 03:00 AM
I've only seen them without the Ethernet port, not as exciting perhaps :), the Ethernet ones I've seen in their product catalog, but I guess not very many people used Ethernet in the early 90's.

Does it really need a recap?, it got those higher quality aluminium can ones.

February 16th, 2012, 01:50 PM
The non Ethernet version doesn't have a cool RAM hack, so you're stuck with 10MBs of RAM.

I was making an assumption from the picture. It looked like leaky cans. If you've already recapped it with new cans, should be good. I usually suggest tantalum capacitors, then you don't have to worry about them ever leaking.