How is the Apple II Plus keyboard encoder supposed to work?

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(Darn, I just typed out a huge message, and when I submitted- it disappeared!)

I've recently acquired an Apple II Plus- and when I turn it on, the power light lights, the speaker beeps, and I see Apple II on the screen and a blinking cursor. However, the keyboard doesn't provide any input- except for CTRL-RESET works. No other keys work.

I've googled a bit- reseated any related chip I could find, verified continuity between keyboard encoder board pins and keyboard, keyboard ribbon cable, etc. No avail.

Can anyone point me to documentation of how the encoder is supposed to work? For example, a closed key switch- how is this "read" by the encoder, and what is sent through the ribbon cable to the motherboard?

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Joined: Jun 5 2008
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Re: How is the Apple II Plus keyboard encoder supposed to work?

see if you can find an online copy of understanding the apple II by Jim Sather.

regards,
Mike Willegal

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Re: How is the Apple II Plus keyboard encoder supposed to work?

Thanks so much Mike! I was able to find one for the IIe- is this machine close enough to the II+ to be useful in this regard?
Jason

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Re: How is the Apple II Plus keyboard encoder supposed to work?

Regarding the keyboard, there's been just enough hardware changes between the classic Apple II and the IIe that you would be better off with the edition for the earlier Apple II. It is out there.

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Re: How is the Apple II Plus keyboard encoder supposed to work?

Ok, I found that one too- thanks guys!!!

One more question: Is -12 volts used anywhere else in the Apple II+, besides one of the two voltages provided to the keyboard encoder chip? I am unable to test my actual machine at the moment, but, I was thinking, if -12 volts was missing from the power supply, the encoder chip would not work (but the keyboard reset button still would reset the 6502, as all it has to do is ground the reset line, outside the encoder chip)

The Apple II comes up, so, if -12 is used somewhere else critical, it perhaps would not let the machine boot?
Jason

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Re: How is the Apple II Plus keyboard encoder supposed to work?

Oops..

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Re: How is the Apple II Plus keyboard encoder supposed to work?

It sounds like the mother board is OK: beep followed by video.
In my experience, the commonest fault closest to what you describe, is damage to one or 2 TTL chips on the discrete encoder board (605-X105-).
The damage is caused by a previous owner taking the machine apart and then re-connecting the keyboard ribbon cable to the motherboard the wrong way around. (I've even done this myself). That is usually enough to blow 1 or 2 of the TTL chips on the encoder board. If one then reverses the ribbon cable back to the correct orientation, reset will then work, but some or all of the keys do not work! Sound familiar?

The chips that blow are either the 74LS04 (14 pin) next to the encoder chip, or the 74LS00 (14 pin) right next to the 74LS04, or both. There is another 74LS00 chip closer to the 555 timer chip that seems to survive this, so you should focus on the 2 chips mentioned that are closest to the encoder chip. BTW: the encoder chip should be OK if the fault was connecting the ribbon cable the wrong way around.

You will need reasonable soldering skills, preferably a solder sucker, to remove those 2 chips, and insert 2 new 14 pin sockets so that in future they are easy to replace. Don't attempt this if you have not done it before as too much heat will permanently damage the fine PCB tracks.

I'd do it for you, but postage might be expensive as I'm across the water in Oz!
Good luck, I'd be interested to hear how you get on...
Laurie

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Re: How is the Apple II Plus keyboard encoder supposed to work?

Oh boy, thank you for the info! I'm actually getting excited that there might be an easy fix to this after all… I have a desoldering station, and I've done a lot of electronics, so this will be an easy fix. And, I think I even have those chips in stock what are the chances? Smile I sure hope this works, thanks again, and I'll let you know what happens

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