//e enchanced open apple / joystick button 0 issue

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//e enchanced open apple / joystick button 0 issue

Greetings everyone, been searching for a solution to this for a long time and just now stubled across these forums.  I hope someone here can help!

 

I've got my original //e enhanced from back in 1984 and it has survived well all these years.  I've only had to replace the RAM in it about two years ago to keep it running.

 

It has, for quite a long while, developed an issue thats extremely frustrating as it affects just about every single game:

 

The Open Apple / Joy Button 0 only works about a third of the time.   Doing a PEEK at the location in a simple BASIC program and tapping the open apple key or pressing the joystick button only registers every few presses.

 

I'm not sure where to begin troubleshooting this one;  any ideas?

 

Thanks!

John

 

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LiveSteamJohn wrote:The Open

LiveSteamJohn wrote:

The Open Apple / Joy Button 0 only works about a third of the time.   Doing a PEEK at the location in a simple BASIC program and tapping the open apple key or pressing the joystick button only registers every few presses.

Do the other buttons work correct? The input signal from the joystick goes directly to a LS251. If there was an issue with an external device probably this input chip may be damaged.

 

Regards

Ralf

 

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Yes, button 1 works perfect,

Yes, button 1 works perfect, as does CLOSED APPLE.  It's just OPEN/Button 0.

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buttonDebug.jpg

 

I just fired it up and wrote the program again (it has been a while since I last messed with this...) and now I'm getting nothing from button 0.

 

In the photo I've just hit button 1 and am pressing button 0 over and over.   Seems like it's gotten worse over time.

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Did some poking around online

Did some poking around online and, perhaps, the issue lies in the multiplexer chip.   Problem is, I can't find an exact match -- found ones that are close but I do not know if they will work.

 

The chip itself is HD74LS251P.

 

I can find an SN74LS215N on Digikey, however I don't know if the P and N designations mean they aren't compatible/the same.   Anyone know if they are?

 

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LiveSteamJohn wrote:The chip

LiveSteamJohn wrote:

The chip itself is HD74LS251P.

I can find an SN74LS215N on Digikey

You see the difference between LS251 and LS215?

You can use any LS251. It's just important to get an "LS" type.

Regards

Ralf

 

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RalfK wrote:You see the

RalfK wrote:

You see the difference between LS251 and LS215?

You can use any LS251. It's just important to get an "LS" type.

Regards

Ralf

 

Thanks!  Got one on order from Digikey.  Fingers crossed this fixes the problem.

 

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Negative, no love for the //e

Negative, no love for the //e.  New chip didn't fix the issue.  Not sure where to go next.

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Unfortunately if the 74LS251

Unfortunately if the 74LS251 didn't fix it, then it is probably either a problem on the motherboard, a bad socket, or worse, the IOU chip (which is unubtanium).  May be time to consider swapping the mobo out.  There are some on eBay at not too ridiculous of prices.

 

If you want to try to diagnose it, and you have another proper revision IOU, you could try swapping that and see if it works.  Unfortunately if it is the IOU, as I said above, those are basically impossible to find anymore so you might have to buy another mobo to get one.  For the other issues, you'll have to look at a schematic and then do continuity tests between the points to see if there is a break somewhere caused by a burnt/broken trace or a faulty socket.  That's labor intesnsive but not expensive.

 

 

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One thing that's odd is that

One thing that's odd is that the open apple functionality is now fixed.   Before the chip swap I could hit CTRL-OA-RESET and it would only work about 1/3 of the time.  Now it works 100% of the time without fail...

 

/scratching head

 

 

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Just got home and decided to

Just got home and decided to poke around (no pun intended) again.  On a whim I plugged in my joystick and ... it works?

 

All the testing I've been doing has just been PEEK'ing the button and it never shows a response (going >127).   But the functionality is actually fixed.

 

Ya got me!
 

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Sounds like maybe you had a

Sounds like maybe you had a bad connection like a dirty socket or something.

 

Glad it is working now.

 

 

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softwarejanitor wrote:Sounds

softwarejanitor wrote:

Sounds like maybe you had a bad connection like a dirty socket or something.

 

Glad it is working now.

 

 

The chip I replaced is direct soldered on the motherboard; I'm convinced it was faulty.

 

It's still a little puzzling as to why I cannot PEEK the location or use the PDL(0) function in BASIC to get an accurate reading when it is working.

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PDL(0) reads tke knob on

PDL(0) reads tke knob on paddles or the joystick axis, not the button.  The buttons and Apple keys are not read the same way.  Are you sure you're PEEK-ing the right location?  For the button 0 it should be PEEK(49249) and for button 1 it is PEEK(49250).  If the value returned by the PEEKs is > 127 then the button is pushed.

 

For a soldered chip it can theoretically have a bad solder joint or the trace could be broken but that is actaully pretty rare.  The 74LS251 could well have been bad.  Anyway, if it is working now it's all good.

 

 

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See my above photo of the

See my above photo of the screen - that's peeking the button zero location.   I wrote an addition to that that also output the PDL(0) and (1) to make sure the X,Y was working good as well.

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