Keyboard problem on my Mac 128K

[meall]

Hi,

I bought recently a Mac 128K on eBay. I repaired the floppy drive, which was sticked into the greace. It is all booting well. The mouse also is good.

But when I try using the keyboard, it does not work at all.

What can be wrong?

What can I do to validate if the keyboard, the cable or the keyboard controller on the MB is defective?

Thanks for any help. I'd like this one to work as a new one.

 

[tomlee59]

There's no easy way to troubleshoot this without another keyboard (or another old mac that uses that type of keyboard). You'll be pretty limited in what you can test for. That said...

Just look carefully at all connections. Look at the plug, look at the jack. Clean/repair/replace as necessary. Open up the keyboard. Look at its internals, especially where the cable connects to the circuit board.

Use an ohmmeter to verify that there's no broken connection from the plug pins to the keyboard's internals. All four pins need connectivity (unlike a phone, which only needs the middle two).

 

[wally]

If you have Larry Pina: Macintosh Repair and Upgrade Secrets First Ed 1990 he has a section on page 217 that your questions and comments encouraged me to read, when I realized it was not ADB! This may be old, but it is all new to me! What I learned tonight in brief was:

1. The correct cable is a straight through cable. Each pin is wired to its same number, position plug conductor at the other end.

2. If a telephone coiled handset cable is unfortunately substituted, the chip in the keyboard on a socket blows, and sometimes the chip at the inside the Mac128 blows too! Phone handset cables connect mirrored plug positions 1:4, 2:3, 3:2, 4:1 and are really bad news!.

3. The Mac128 intended keyboard is MO110, no suffix A. But the MO110 is mutually interchangeable with the MO110A. There is a replaceable 8021H or 8415 located near the caps lock key for the MO110, and a replaceable 8550 or 8728 on a socket under the spacebar in the MO110A model .

4. No info found on the Mac128K end of troubleshooting this.

So right off, it's important to make sure the cable is the right straight through kind, when the plugs are both held in parallel pointing towards you, leftmost position better connect to the other leftmost position, etc.

 

[tomlee59]

Occasionally, you will run across a keyboard that's been blown by a reverse-connected cable, but it's rare. The RJ11 connector is wider than the one used in the Mac, so you have to shave it down to fit. If the original cable is still attached to that keyboard, it's even less likely that this is the problem.

Your post made me sit and think about all the old macs I've fixed, and what keyboard problems I've come across. I could only recall one totally dead keyboard (from a 128K), and it was fried by a can of Coke accidentally dumped into it. Washing didn't restore it to health, so some grand short blew something good.

Again, just do a careful visual inspection as a first step. Then, depending on how desperate or determined you are to do more, post back, and someone will undoubtedly chime in with additional things to try.

 

[meall]

Occasionally, you will run across a keyboard that's been blown by a reverse-connected cable, but it's rare. The RJ11 connector is wider than the one used in the Mac, so you have to shave it down to fit. If the original cable is still attached to that keyboard, it's even less likely that this is the problem.

I don't think wally was talking about a phone cord of type RJ11 that string into the wall, but the phone coiled cord that plugged into the handset of the phone itself. This one as the same connector as the Mac 128K keyboard. It is a kind of RJ11 with thinner connector.

That said, I have the original keyboard cable. One told me that the phone handset keyboard should work, try it, does not, know I know why. But the keyboard was not working before that's for sure. I'm surprise that this could burn the keyboard so far...

I can also try to validate the cable pins with a multimeter to see if the cable has all pins connected pass throught, too, now that I know the pin-out.

Finding a new keyboard for the Mac is rare, unless someone has this handy somewhere!

 

[meall]

I finally bought a new keyboard and a cable, and it happen to be the cable that was not working.

Thanks for your help.

 

[JDW]

Many computer cables are pretty straightforward to diagnose with any el-cheapo DMM that has a continuity check feature. (Continuity checks help determine if there are breaks in wires in a given cable.) Just put the multi-meter in that mode (which may be "diode check" mode on some DMMs) and put one problem on a pin at one end of the cable and the other problem at a pin at the connector on the other end. It's even easier to do this if your DMM beeps instead of just giving a readout of zero, that way you don't have to keep your eyes on the meter when you check.

The reason I say this is because you don't always have to purchase new equipment to solve these problems. If you just like to have spare parts, that's fine. But many people by old Mac stuff on EBAY, which can often be rather high priced (for decent, clean equipment). So if you are a classic Mac lover, even if you aren't an electrical engineer or technician, a DMM would be a good tool to have around the house, just as a hammer or screw driver would be.