Macintosh SE with S-video instead of ADB cable won't boot

[PotatoFi]

I am thrilled that the CRT is now working in my Macintosh SE FDHD! If you want to read about that issue, you can do so here. So now, I've got the Macintosh SE, a keyboard, and a mouse. Unfortunately, I do not have an ADB cable (one is on order). In the meantime, I decided to try using an S-video cable, since the pinout appears to be the same. Also, The Internet(tm) which is never wrong said that S-video cables make great ADB cables (although ADB cables don't make great S-video cables). Figuring I was pretty safe, I connected the keyboard with an S-video cable but found that the machine hangs during boot. I believe it hangs around "Welcome to Macintosh". 

I discovered that it even does this if the keyboard isn't connected to the S-video cable; there's a hang when only the S-video cable is connected. Needless to say, I'm not trying that S-video business again... I'm waiting for my ADB cable!

Does this sound like normal behavior? What is it about an S-video cable that might cause this? Any chances that my keyboard is bad? Also, is there a way to enter text on this thing without a keyboard?

 

[Daniël]

It's not the cable. ADB and S-Video cables are wired up exactly the same. Maybe the SCSI Hard Drive's gone bad? Have you tried booting from floppy? Make sure the floppy drive is lubricated before you use it, chances are high you will destroy the eject mechanism gears otherwise!

 

[PotatoFi]

Hrm, the machine is booting just fine via floppy and hard drive without the S-video cable. I've been using the machine for several hours with just a mouse, and I've rebooted it many times. Zero issues if the S-video cable isn't connected. Should I perhaps try another S-video cable?

I will take your advice on the floppy drive. I'll pull it out and lubricate it tonight.

 

[AwkwardPotato]

Try another S-Video cable -- some of the ones I've found tie both GND lines together, which are the Data and Reset lines on the ADB connector.

 

[PotatoFi]

Try another S-Video cable -- some of the ones I've found tie both GND lines together, which are the Data and Reset lines on the ADB connector.

Sure enough, that's the problem. Both pins 1 (GND) and 2 (GND) are tied together. Moral of the story: perform a continuity test before using an S-video cable as a temporary ADB cable!

 

[PotatoFi]

Uh-oh... bad news. Got my ADB cable in, and the keyboard does not work. The mouse connected through the keyboard works fine, which tells me that my ADB cable is fine.

Did I fry my keyboard?

 

[techknight]

Yea, probably. You accidentally connected signal lines together that arnt designed to be connected in that manner.  I am highly surprised you did not kill the ADB IC in the SE. 

But then there is also the factor of which I have no idea if the keyboard even worked prior, so theres that. 

 

[PotatoFi]

But then there is also the factor of which I have no idea if the keyboard even worked prior, so theres that. 

Neither did I, since I retrobrighted it before having a woking SE to test it on. But good news! I posted too soon. When I took it apart, I must not have connected the ribbon cables securely. I reseated them and now it's working great. I'm still going to be very wary of S-video cables...