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CharlieFrown

Lost Mac Plus keyboard cord

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Hi, seems that it's lost. I've seen one on eBay, but considering shipping costs there's no way I am paying $40 for a simple cord! 

I am aware of arduino solution, but I just want to use my Apple keyboard. Any way I can modify telephone cord?

 

Charlie

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Mac Plus is a straight through cable and a telephone has crossed wires. With a 4P4C connector and crimp it's easy to make a new cable.

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I made a post in your WTB topic before I saw this topic. I will repeat what others have said: you can make your own keyboard cable in about an hour's time as long as you have: scissors, soldering iron, and a telephone handset cord.

 

You just cut the cord in two, then reverse the wire connections. You'll see they're colored, so just flip one side of the cut cord around and solder it back together. I'm going to write an entry on doing this in my Mac 512K blog pretty soon; I did it myself about 3 or 4 weeks ago.

 

Once you do this, the cord won't work on the telephone anymore. That's the only downside. ;-)

 

On December 8, 2017 at 11:07 AM, techknight said:

 I do know if you plug in the cable that is wrongly pinned, it will FRY the keyboard. 

Not true. Neither the Macintosh nor the keyboard will be harmed. Look at the pinout in Inside Macintosh.

 

I tried it out before I cut the telephone cord, and it will not harm the Macintosh or the keyboard. All that happens is that nothing happens. ;-)

Edited by Dog Cow

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I am not aware of damage to the keyboard, the old tech notes say the controller on the motherboard is what gets fried. There is no mention of the keyboard being damaged but I suppose its possible.

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13 hours ago, techknight said:

Then you can explain that to the dead keyboard I have from doing this way back in the day. 

Static electricity?

 

I did the deed, I even opened Key Caps and typed on the thing. No keypresses were registered. When I swapped in the correct Mac keyboard cable, now I could type. Mac and keyboard were unharmed.

Edited by Dog Cow

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On 12/10/2017 at 5:47 PM, Dog Cow said:

Static electricity?

 

I did the deed, I even opened Key Caps and typed on the thing. No keypresses were registered. When I swapped in the correct Mac keyboard cable, now I could type. Mac and keyboard were unharmed.

No, not static electricity. As techknight says, you were lucky, plain and simple. You shouldn't assume that everyone else would be as lucky as you.

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1 hour ago, tomlee59 said:

No, not static electricity. As techknight says, you were lucky, plain and simple. You shouldn't assume that everyone else would be as lucky as you.

Or maybe the reverse is true. Maybe we shouldn't assume that using a telephone handset cable will harm either the Mac or the keyboard or both.

 

How do we know it's not static electricity? I think we need more people to try this and see what happens.

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11 hours ago, Dog Cow said:

How do we know it's not static electricity? I think we need more people to try this and see what happens.


Or maybe that's a really foolish and terrible idea?

 

According to the pinout if you use a rolled telephone cord in place of Apple's cord you'll be putting +5v to ground on the keyboard end, which is plenty to destroy integrated circuitry of that era. The fact that it didn't happen to you could be, as mentioned before, "luck", or I suppose it's possible, depending on the vintage of your keyboard, Apple might have started fitting the ground line with a protective diode just in case to cover users if they made this mistake. (That's utter speculation based on nothing, I don't plan on cracking open the two RJ-11 keyboards I have to see if there might be a difference like that between the early keypad-less one and the plus keyboard.) Seriously, don't just "try it" unless burning up old computers is your idea of a good time.

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1 hour ago, Gorgonops said:


That's utter speculation based on nothing, I don't plan on cracking open the two RJ-11 keyboards I have to see if there might be a difference like that between the early keypad-less one and the plus keyboard.) Seriously, don't just "try it" unless burning up old computers is your idea of a good time.

 

Dan Kottke, digital engineer at Apple who co-designed the Macintosh keyboard with Ed Riddles, says otherwise:

 

"The keyboard connects to the Macintosh via a modular coil cord that is similar to those used on telephones. The Mac's cord has heavier gauge wire to prevent drops in voltage that don't stop you from understanding phone conversations but can interfere with the accuracy of the digital signals the Mac uses. Ifyou replace the Mac's cord with a telephone handset cord, it doesn't damage the keyboard's microprocessor, but it won't work. "

 

Source: MacWorld Sep-Oct 1984, pg 35.

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I'm sure Dan had collected a large quantity of experimental evidence on the Mac 128, Mac 512 and Mac Plus and all their associated keyboards and revisions by August of 1984, but you will excuse me if I don't accept this as authoritative, despite the source.

 

Given the variables involved and scads of evidence that others have lost hardware over this, I will not be plugging phone cords into my vintage Macs.

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1 hour ago, Dog Cow said:

 

Dan Kottke, digital engineer at Apple who co-designed the Macintosh keyboard with Ed Riddles, says otherwise:

 

"The keyboard connects to the Macintosh via a modular coil cord that is similar to those used on telephones. The Mac's cord has heavier gauge wire to prevent drops in voltage that don't stop you from understanding phone conversations but can interfere with the accuracy of the digital signals the Mac uses. Ifyou replace the Mac's cord with a telephone handset cord, it doesn't damage the keyboard's microprocessor, but it won't work. "

 

Source: MacWorld Sep-Oct 1984, pg 35.

Note that Dan is a digital engineer. He has clearly not run many (or any) experiments, and is just voicing an opinion. He would not get a good grade in my circuits classes. His answer about the "heavier gauge wire" is utter nonsense. The currents flowing (both signal and power) are so small that any voltage drops would be completely negligible. The real reason for the incompatible cable is simply that Apple has traditionally wanted to force users to buy Apple widgets.

 

In contrast with Dan, I'm an expert in the sense that I have learned from the vast number of mistakes I have made, or have seen others make, whence wisdom and scar tissue derives.

 

When you use an ordinary telephone cable in place of the correct keyboard cable you are applying power to the keyboard in REVERSE POLARITY. You are not simply "grounding 5V". Although doing so doesn't guarantee keyboard destruction, it certainly makes it likely. You are relying on the Mac's power supply limiting the current to a value below that which would destroy the keyboard electronics. That's an unsafe bet, as the current limit is set to protect the power supply, not devices connected to it.

 

As to your static electricity hypothesis, note that the impedance levels are much reduced on the keyboard when reverse polarized. If static electricity were strong enough to destroy the keyboard in that condition, then you would see a great many failures from static electricity when using normal cables.

 

It ain't static. It's reverse polarity. No more experiments needed, and no appeals to Kottke's ill-founded opinions will change that.

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58 minutes ago, tomlee59 said:

When you use an ordinary telephone cable in place of the correct keyboard cable you are applying power to the keyboard in REVERSE POLARITY. You are not simply "grounding 5V".

 

To be clear, that's what I said, if not quite so clearly; you're applying +5v to the side of the circuitry in the keyboard that's supposed to be connected to ground.

 

(Obviously the real "ground" in the circuit is on the Mac side, not the keyboard. And, yes, by flipping the leads you've connected the "positive" side of the keyboard to that. So yes, if current flows it's going to be in reverse.)

 

Seriously, there's no defense for suggesting people try this for laughs *and* that quote from the Apple "engineer" is just gobbledygook. Telephone cables work if you cut the end off and flip the pinout, Dog Cow said that himself, for sheesh's sake! 

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1 hour ago, tomlee59 said:

Note that Dan is a digital engineer. He has clearly not run many (or any) experiments, and is just voicing an opinion. He would not get a good grade in my circuits classes. His answer about the "heavier gauge wire" is utter nonsense. The currents flowing (both signal and power) are so small that any voltage drops would be completely negligible. The real reason for the incompatible cable is simply that Apple has traditionally wanted to force users to buy Apple widgets.

 

In contrast with Dan, I'm an expert in the sense that I have learned from the vast number of mistakes I have made, or have seen others make, whence wisdom and scar tissue derives.

 

When you use an ordinary telephone cable in place of the correct keyboard cable you are applying power to the keyboard in REVERSE POLARITY. You are not simply "grounding 5V". Although doing so doesn't guarantee keyboard destruction, it certainly makes it likely. You are relying on the Mac's power supply limiting the current to a value below that which would destroy the keyboard electronics. That's an unsafe bet, as the current limit is set to protect the power supply, not devices connected to it.

 

As to your static electricity hypothesis, note that the impedance levels are much reduced on the keyboard when reverse polarized. If static electricity were strong enough to destroy the keyboard in that condition, then you would see a great many failures from static electricity when using normal cables.

 

It ain't static. It's reverse polarity. No more experiments needed, and no appeals to Kottke's ill-founded opinions will change that.

 

I take it you dont know who Dan is....

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