Apple IIe Platinum Repeating Key Issue

[GeoffB]

Hi Everyone,

 

I recently purchased an Apple IIe Platinum and it arrived in working condition. I was able to power it up, enter a simple BASIC program, start the monitor and dump memory, etc. But not long after, they keyboard stopped working. What happens now is as if a particular key is stuck down and repeating constantly. It overflows the line buffer, prints a "\", beeps, then repeats the whole thing again.

 

Things I've tried:

• Googling...
• Reading the couple of posts on here about similar issues (but not the same as mine)
• Removed all socketed chips (CPU, CF ROM, MMU, Video ROM, Keyboard ROM, AY3600, the HAL, and 2 74xxx logic ICs around position C11/12), thoroughly cleaned both sides of the board, and re-inserted the chips
• Tested the keyboard switches (all of them... ?)
• Pressed firmly on a bunch of chips and watched - the AY3600 didn't do much, but pressing the keyboard ROM did seem to change the character being repeated
• Re-soldered the pins for the keyboard ROM (which stopped it from changing the repeating character, but didn't fix the problem)

 

All of the above has been done in-situ, and now with all add-in cards removed and the board on the bench out of the case. No change.

 

In playing around the other night, I tried removing the AY3600 and noticed that the problem continued. I then removed the keyboard ROM and the problem still continued! To be clear, this is both the AY3600 and keyboard ROM removed from the board, and the problem is still there. ?

 

I don't really know where to go now. Could this be the IOU? I don't have another one to piggy back, which makes it hard.

 

I'm thinking about re-soldering all the ICs on the board just in case, but it feels a bit sledgehammer-y. There doesn't appear to be any issues with traces, and there's no corrosion on the board anywhere. The machine boots and displays, and I can reset it and run the self test with a pass result.

 

It was working fine, and now it's unworking... ? And I just bought a Floppy Emu, although I understand the Booti is the thing to get nowadays?

 

Any ideas that could help would be hugely appreciated.

 

[DistantStar001]

Honestly, from the symptoms you described, it sounds like your problem is with the keyboard and not the motherboard.  Does the repeating key start immediately following boot to BASIC?  And if so, is it the same key every time?  

 

If this is the case, try pressing a different key and see if the repeating character changes to the new key pressed.  If that's the  case, then the switch on the first key is likely shorted.  It could be intermittent in a way that your multimeter can't detect, or there could be a piece of conductive debris in the switch that moves out of the way when you turn the board over and then falls back in when the switch is right side up.  I'm basing this on a similar malfunction I get with my //e's cleaning switches with alcohol.  The alcohol gets in, shorting the switch until it evaporates.  Essentially, the computer thinks that I'm holding the key down.  My guess is that something similar is happening here.

 

I would suggest desoldering the switch from the keyboard and see if the problem persists absent the suspected switch.  If not, then all you need to do is replace the switch (or take it apart and clean it out) and then you're good to go!  ?   

[GeoffB]

Hi! Thanks for replying. Sorry my reply took so long.

 

I've done some more investigating and it's definitely not the keyboard, and I don't think it's the keyboard ROM.

 

I booted the machine, waited for the repeating input to start cycling (only takes a second), then unplugged the keyboard from the mainboard and the problem continued. Keyboard connected/disconnected makes no difference.

 

Playing with the chips again, I noticed this:

• I pulled the AY3600 (machine off, obviously) and the repeating continues in the same style - usually a space or a random number
• I pulled the keyboard ROM, and the repeating continues, but now it's a random set of graphical characters, typically a solid square or a dithered square

This leads me to believe that the keyboard ROM is fine as it appears to be translating the output of the AY3600, although it's rubbish. I've got three AY3600 chips here, and it doesn't matter which one I put in, the result is the same. It's also the same with it removed, so I think that rules out the AY3600.

 

Pressing firmly on the AY3600 does alter the pattern. It may switch numbers, or end the buffer input early. Removing the AY3600 and pressing firmly on the socket has the same effect. I'm going to try resoldering the AY3600 socket next.

 

I also thought I saw a change when I tapped on some of the resistors and caps around the AY3600 and keyboard ROM, but I'm not 100%. I think I'll just have to keep tapping things and resoldering them as a process of elimination.

 

I've got another Platinum 2e on the way, so I'll be using that to double-check all the socketed chips, etc.

[GeoffB]

Right, so it's fixed now! ?

 

I flipped the board over and watched the pads as I pushed on the AY3600 and couldn't see anything bad. I decided to grab a schematic and do some continuity testing. (This is the schematic here: https://ia800201.us.archive.org/25/items/apple_iie_ntsc_schematic/apple_iie_ntsc_schematic.pdf). All the pins from the AY3600 to the keyboard ROM were fine. I started tracing from the keyboard connector to the AY3600 and found I had a problem with connector pin 6 and AY3600 pin 20. When I pushed a little harder against the pin on the AY3600, I was able to get continuity. When I just rested it on there, I didn't. Must be a dud socket! I had another (better, but not machined) one here, so desoldered the old one and put the new one in. Continuity was back! Popped the AY3600 into the socket, fired up the ol' girl, and it's good!

 

I've put the whole thing back together now and it's running like a dream. About to test out the Floppy Emu.

 

Case closed. For now...

[potatohead]

Excellent!

 

Another Apple back in service!

[Papalapa]

Good job, well done!