Mac 512k Keyboard (M0110) Not Working

[jwse30]

I finally got around to repairing my Mac Plus (had to retouch solder joints on analog board to CRT connector). I bought this machine last summer mostly for the SCSI external hard drive case it came with, but also so I could test a few keyboards that are collecting dust in my basement. The Plus is working fine now, and I upgraded it to 4m of RAM while I was in there.

I have three of the telephone jack keyboards; two are M0110a, and one is the M0110. The two M0110a's work fine with the Plus (tested by using the little Keycaps program), but the M0110 doesn't do anything when hooked up. I examined the jack and everything looks normal to me. I then opened up the keyboard, half expecting to find some evidence of a magic smoke leak, but everything looks good albeit a bit dusty. I blew out the dust with canned air just in case to no avail.

Can someone point me in a general direction that might get this keyboard working again? Is there a common failure point? Google had lots of hits for partially working units, but nothing on dead ones.

Thank you in advance,

J White

 

[Stephen]

I'm somewhat experienced with the M0100. Have you used a multimeter to check the port inside the keyboard while it's connected to the Mac Plus? You should expect the outside wires on either side to read 5 volts. If you have an oscilloscope you can also probe either of the middle wires + ground. You should see pulses when the keyboard is connected.

Let me know what tools you have available to test with.

 

[jwse30]

I was thinking of checking the jack with an ohmmeter, but my meter isn't really meant for checking such small items (I'm an industrial/power distribution electrician) and the probes I have barely fit in 110v outlets. I am planning on looking for a phone headset cable and cutting an end off and stripping the individual wires out to test.

Ive got no practical access to a scope.

I will report back with ohm readings and voltage readings once I procure a test cable. Thanks for pointing me in a direction!

J White

 

[jwse30]

Well, I soldered a few pieces of paper clip to my leads on my meter. I get 4.6x volts on the outer pins. But then something odd happened. I must have shorted something out on the pins because the keycaps app went from the small keyboard to the keyboard with numberpad on the screen.

Anyhow, The ohm readings were pretty goofy (with the cable disconnected) in that almost everything was reading to everything else. I was able to get the four pins inside the jack to read about 3 ohms (I am sure the paper clip solder job accounted for that). After that I plugged the cable in and fired up the machine. I was reading 4.7 volts between the outer pins directly under the jack. I didn't check to the traces for some reason. I don't have a scope handy, so I did not check for the pulses on the middle pins.

Have you any other suggestions?

Thanks,

J White