Diagnostics loop

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Joined: Nov 12 2017
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I recently acquired a IIe enhanced and when it's switched on it appears to enter the built-in diagnostics without any input from me. The usual screen images happen and the beeps at the end, however instead of a message it simply starts over. If I force it into diagnostics with the keyboard it goes through the routine and then gives me the "SYSTEM OK" message. I've removed and re-seated the ICs and thoroughly checked as well as cleaned the motherboard. It shows no corrosion or any signs of contaminants and looks very clean and undamaged.

Any suggestions as to what the cause could be would be much appreciated.

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Joined: May 27 2009
Posts: 936
Re: Diagnostics loop

Problem with OpenApple/ClosedApple or joystick buttons?

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Joined: May 27 2009
Posts: 936
Re: Diagnostics loop

Problem with OpenApple/ClosedApple or joystick buttons?

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On a clear disk you can seek forever..

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Joined: Nov 12 2017
Posts: 2
Re: Diagnostics loop

Keatah wrote:

Problem with OpenApple/ClosedApple or joystick buttons?

Thanks for the response. It does the same thing when the keyboard is unplugged. I've heard that a bad LS251 could be the issue, but I'm hoping for suggestions that don't involve removing and replacing a soldered-in part. I don't know how to test the chip on-board so this may be my only option if nothing else is suggested. My hope is that someone has dealt with this before and can say with near certainty what it is.

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Joined: Jan 29 2012
Posts: 194
Re: Diagnostics loop

Hi RuneRider,

There is an old tech trick you can try provided the chip is not shorted. Purchase a brand new LS251 chip and bend the legs slightly and place it down over the suspect LS251. Make sure the orientation is correct!!! i.e. the little notch in the one on the board matches the little notch direction on the one ou are placing down.

Make sure all the pins of the new one are making contact with all the pins of the one mounted to the board. Carefully turn the PC on and see if it works while carefully holding the new chip in place. If it does, then it is safe to de-solder and repair. If it doesn't then unfortunately that doesn't tell you much.

I'd then grab a copy of the SAMs repair guide for the Apple IIe. If you have an o-scope, that guide may give you an idea what should be coming from the chip.

Thanks,
Jay

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Joined: Dec 20 2008
Posts: 210
Re: Diagnostics loop

Note- without a keyboard connected, the diagnostics will always run as you describe.

However, what you describe is odd with the keyboard connected.

You tried another keyboard?

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Joined: May 27 2009
Posts: 936
Re: Diagnostics loop

Don't forget and check the 470 Ohm resistors. They pull PBO and PB1 to ground. And pressing CAPL or OAPL pull them high.

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