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Apple II+ broken - does not boot

Submitted by jaksel on July 16, 2006 - 9:40pm. Apple II

I have an Apple II+ which broke many years ago. My father believes one of the expansion cards was not properly inserted in the slot, causing it and the computer to stop working.

I would really like to repair this computer, but I am not sure what is broken. When I power-up the screen is just full of garbage, like "??EE??EE" or something like that. There is no beep, and no activity in the disk drive. It seems like most circuits are in fact running (could only check this with a DC volt meter; not the best way...). Thus it seems like the master clock is running, and the character generator ROM and at least some of the RAM is probably OK.

Any ideas on how to fix it? Where to begin searching for the problem?

BTW I also have an Apple IIe clone from Redstone, which works like a charm. I played lots of old games today, and got really nostalgic ;-)

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david__schmidt's picture

Re: Apple II+ broken - does not boot

Submitted by david__schmidt on July 17, 2006 - 3:08am.
jaksel wrote:
I would really like to repair this computer, but I am not sure what is broken. When I power-up the screen is just full of garbage, like "??EE??EE" or something like that. There is no beep, and no activity in the disk drive.
Take a look at this discussion thread: http://www.applefritter.com/node/18248 it has some good advice and additional pointers.
jaksel wrote:
BTW I also have an Apple IIe clone from Redstone, which works like a charm. I played lots of old games today, and got really nostalgic ;-)
Yeah, that'll happen. :-)

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mmphosis's picture

a couple of easy things to try

Submitted by mmphosis on July 17, 2006 - 7:11pm.

- I've had faulty cards stopping my Apple II+ from booting.

Carefully remove ALL expansion cards, even the disk controller card (with the computer turned off, of course you know that.)

- sometimes a chip may have become unseated.

Next, with the computer turned off, ground yourself and carefully push down on the ICs to make sure that they are seated in the sockets okay.

Turn on the computer. Good luck! Beyond that, does anyone else have any ideas?

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Basic computer debug

Submitted by glb_gtz on July 18, 2006 - 3:28pm.

With any computer that will not boot, the basic debug approach is to remove everything that is not essential for booting. This includes any extra memory and peripherals. From this point, swap as many parts that you can with a known good system. If possible, I would exchange the CPU and memory from the clone. But this might also kill the good parts, it is unlikely, but possible.

Good luck with the debug.

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Found the problem!

Submitted by jaksel on August 6, 2006 - 10:56am.

I got my Apple II+ to the place I work, and used a mixed-signal oscilloscope for searching for errors. It turned out that the 8T28 bus transceiver at H10 had failed in one of the drivers, causing signal D1 on the data bus to permanently be pulled low, so that a logic 1 was only at 400 mV (should be ca 3 V for ROM outputs it seems). Replacing with a new chip, possibly another type since it seems 8T28 is obsolete, should fix it.

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Fixed it

Submitted by jaksel on April 4, 2008 - 6:13pm.

This is a late post...

I fixed my Apple II+. It turned out to be two faulty RAM chip. To debug I first powered on and off the Apple to see a consistent pattern on the screen. Then I started swapping RAM chips one by one, and after each swap I powered on the Apple to see if the pattern would change. When it did I replaced that chip with a new one (I ordered lots of new ones from the Internet).

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