05-06-2012, 12:03 PM

I have a Macintosh 512K that still functions to this day, but what doesn't function, is the keyboard. I was wondering how I could test if the problem is the logic board or the keyboard. I believe there is power running through it because the keyboard gets warm on the space bar. But I cannot type!

05-06-2012, 12:17 PM

My first thought is...I think that there's almost no way that the keyboards space bar is getting warm.

There's really not enough electricity flowing thru the 512's keyboard cable to make anything warm...and if we were to disassemble the keyboard...you would see that the spacebar itself is so far removed from any electronics (or heat source) that something inside the keyboard would have to be REALLY overheating to get the spacebar warm.

These keyboards are VERY very simple in design...there just isn't much in there to make things warm. But maybe I'm wrong...you're certainly right there experiencing things.

In any case...if the computer is working fine...then the problem probably isn't the logic board (and you don't want it to be)...since there's very little chance of you getting a replacement logic board at this point 27-28 years later.

Most likely (if nothing on the keyboard is working)...the keyboard cable or the keyboard itself may have gone bad...and these two things would be a much better place to start in terms of troubleshooting. Of course you will need parts...gotta check out e-Bay...for folks selling old (but still working keyboard cables & keyboards).

Don't be too shocked when you see the prices!!

- Nick

05-06-2012, 12:32 PM

The Mac 512 is like the first Mac and uses a Telephone like cord that plugs into the front. Those cables after years of use often fail. They are wired differently than a telephone handset cord though. There is a wiring diagram somewhere on the net. Will see if I can find it for you and post back.

05-06-2012, 01:08 PM

Originally Posted by pigoo3

My first thought is...I think that there's almost no way that the keyboards space bar is getting warm.

There's really not enough electricity flowing thru the 512's keyboard cable to make anything warm...and if we were to disassemble the keyboard...you would see that the spacebar itself is so far removed from any electronics (or heat source) that something inside the keyboard would have to be REALLY overheating to get the spacebar warm.

These keyboards are VERY very simple in design...there just isn't much in there to make things warm. But maybe I'm wrong...you're certainly right there experiencing things.

In any case...if the computer is working fine...then the problem probably isn't the logic board (and you don't want it to be)...since there's very little chance of you getting a replacement logic board at this point 27-28 years later.

Most likely (if nothing on the keyboard is working)...the keyboard cable or the keyboard itself may have gone bad...and these two things would be a much better place to start in terms of troubleshooting. Of course you will need parts...gotta check out e-Bay...for folks selling old (but still working keyboard cables & keyboards).

Don't be too shocked when you see the prices!!

- Nick

Nick, I have opened up the keyboard and saw that there is a little bump in the center of this long chip underneath the spacebar. It also looks like some sort of liquid is was once on the sticker over the chip. (The bump is also under the sticker.) If you need a photo, I can send it.

05-06-2012, 01:20 PM

Originally Posted by pigoo3

My first thought is...I think that there's almost no way that the keyboards space bar is getting warm.

There's really not enough electricity flowing thru the 512's keyboard cable to make anything warm...and if we were to disassemble the keyboard...you would see that the spacebar itself is so far removed from any electronics (or heat source) that something inside the keyboard would have to be REALLY overheating to get the spacebar warm.

These keyboards are VERY very simple in design...there just isn't much in there to make things warm. But maybe I'm wrong...you're certainly right there experiencing things.

In any case...if the computer is working fine...then the problem probably isn't the logic board (and you don't want it to be)...since there's very little chance of you getting a replacement logic board at this point 27-28 years later.

Most likely (if nothing on the keyboard is working)...the keyboard cable or the keyboard itself may have gone bad...and these two things would be a much better place to start in terms of troubleshooting. Of course you will need parts...gotta check out e-Bay...for folks selling old (but still working keyboard cables & keyboards).

Don't be too shocked when you see the prices!!

- Nick

Hey Nick, I just realized something, I am using a Macintosh Plus keyboard (Model number M0110A) with a Macintosh 512k (keyboard model number M0110). Would that have any affect over the keyboard operating?

05-06-2012, 01:29 PM

Originally Posted by zoom01

Would that have any affect over the keyboard operating?

I don't think so. The keyboards for the very early (compact "All-In-One" Mac's) were essentially the same from Mac 128k thru the Mac Plus.

And if this is the keyboard you have been using (successfully up to this point)...then that would also indicate that it was ok to use with a Mac 512.

It sounds like it's probably the cable (since nothing is working). If some keys were working & some not...then it would probably be the keyboard. And the last (and most undesirable option) would be something wrong with the logic board.

05-06-2012, 01:30 PM

Originally Posted by zoom01

Nick, I have opened up the keyboard and saw that there is a little bump in the center of this long chip underneath the spacebar. It also looks like some sort of liquid is was once on the sticker over the chip. (The bump is also under the sticker.) If you need a photo, I can send it.

Does this "little bump" look like it's not supposed to be there? If so, then that could be a problem.

- Nick

05-06-2012, 01:55 PM

Well, I will send a photo. I am not sure if it should be there or not. And no, I bought this computer off ebay last year and the keyboard hasn't worked since. I plugged the keyboard in just now and fired up the Macintosh and after about a minute or two of idle, I felt the spacebar and it did not feel room temperature. It felt a little hotter. Anywho, here is the photo:

Pictures by cburk01 - Photobucket

05-06-2012, 02:21 PM

Originally Posted by zoom01

Well, I will send a photo. I am not sure if it should be there or not.

Thanks for the photos...they always help.

Originally Posted by zoom01

And no, I bought this computer off ebay last year and the keyboard hasn't worked since.

I see. When you mentioned(in post #1)..."I have a Macintosh 512K that still functions to this day..."...I though you meant that it WAS working 100%...and only recently the keyboard stopped working.

Originally Posted by zoom01

I plugged the keyboard in just now and fired up the Macintosh and after about a minute or two of idle, I felt the spacebar and it did not feel room temperature. It felt a little hotter.

Yes...that chip under the space bar is pretty sizable...and I could see how if it was over-heating...that the spacebar could warmup. That "bump" looks (where the label is on the chip) a little brown & slightly "burnt" looking...like some serious heat buildup is or has been taking place. So I would say that the "bump" is not a "good thing" and shouldn't be there.

So here are a few possibilities:

1. The keyboard could be bad (I mean due to that burn-mark/bump...it is bad)...but the keyboard may or may not be the source of the problem.
2. The keyboard cable could be bad.
3. This theory is a bit more complex (see below).

Like "dtravis7" mentioned above. The keyboard cable looks like an old coiled telephone cord. Original keyboard cords for these old Mac's are somewhat hard to find (if someone needs one)...and if you do find them (e-Bay) that can be expensive (for what they are).

So what can be done is...if someone has an old telephone cord...it can be modified to work with the keyboard/computer on these old Mac's. The plug connectors (on old phone cords) are the same as the original keyboard cable for the Mac...but the 4 wires in the cord need to be reversed to work with a Mac.

So long story short (for idea #3). If your keyboard cord looks like it has been "fiddled" with...someone may have tried to substitute an old phone cord for the original keyboard cable...did a bad job of modifying it..and this caused the problem. OR...someone literally substituted an "unmodified" old phone cord (not realizing it needed to be modified first)...and this is what destroyed (so to speak) the keyboard.

Thanks again for the photos!

- Nick

05-06-2012, 02:36 PM

I wanted to add. I just took apart one of my OLD Mac 128/Mac 512/Mac Plus keyboards (model M0110A)...and that "bump" is NOT present on the large chip below the space bar.

So the "bump" (and what looks like a burn/brown mark)...probably shouldn't be there.

- Nick

05-06-2012, 03:19 PM

Nick,


Thank you so so much for the information. Could you send me a photo of what your keyboard cable looks like? Now come to think of it, this cable I have is about two times the size of the Mac Plus keyboard itself and is one third straight, and roughly two thirds curled.

- John

05-06-2012, 03:35 PM

Originally Posted by zoom01

Nick,

Thank you so so much for the information. Could you send me a photo of what your keyboard cable looks like? Now come to think of it, this cable I have is about two times the size of the Mac Plus keyboard itself and is one third straight, and roughly two thirds curled.

- John

No problem. Yes that cord that you describe sounds like a "regular" old coiled/curled telephone cord. The computer keyboard cord we're talking about...has no straight section (it's all coiled/curled).

Believe it or not...I bought 4 of them a couple months ago from a guy on e-Bay (I needed multiple). Total length of the cord (not stretched) is 12" (about 3.5" shorter than the total width of the keyboard...15.5"). This does not include the stubby straight parts with the connector on it.

I posted a thread here on Mac-Forums about it...and here's the photo I had with the post:



- Nick

05-06-2012, 03:58 PM

Syrinx Homepage - Mac Plus Keyboard Cable

Like I thought the wiring at one end of a standard telephone handset cord is backwards on one end and will reverse the polarity of the 5-Volts and probably blow the keyboard.

BTW, A Plus keyboard will work just fine. I use one here on my 512 and Plus.

05-06-2012, 04:28 PM

Originally Posted by dtravis7

Syrinx Homepage - Mac Plus Keyboard Cable

Like I thought the wiring at one end of a standard telephone handset cord is backwards on one end and will reverse the polarity of the 5-Volts and probably blow the keyboard.

BTW, A Plus keyboard will work just fine. I use one here on my 512 and Plus.

Nice link!

- Nick

05-07-2012, 03:43 PM

O.K. so I found a nice $50 keyboard (not $140 like others) and was wondering if I had the right cable. The product description said an RJ11 keyboard connecter. Is that what I need? I don't know if you can see the product description like I can but here is an ebay link:

Apple iMac Mac keyboard Model M0110A Excellent | eBay

(UPDATE: yes scroll down you can see the description.)