//e motherboard troubleshooting

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//e motherboard troubleshooting

So I have a //e motherboard that I aquired from another AppleFritter member recently along with a few other things like a keyboard and power supply.  I was able to replace the blown RIFA in the power supply and get it working and the keyboard appears to be very nice.  The motherboard came sans CPU, so I dropped a Rockwell 6503 that I had into it.  But I'm getting nothing at all, no video.  I also tried a WDC W65C02 in an adapter in it, same result.  I put a A2VGA card in and that reports "No bus activity".  I tried a different power supply and the first one I tried works fine with another //e so I'm sure it isn't a power issue.  Both of the CPUs I tried also work fine in the other //e.

 

I'm not sure where to start with this one.  I've had ][+ and clones with similar deadness but this is the first time I've encountered a //e with no signs of life at all.  I guess I can start swapping chips from a working //e if nobody has an idea where to begin.

 

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I suggest starting on page 4:

I suggest starting on page 4: Sams Computerfacts Apple IIe_alt.pdf

 

 

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Yeah, that looks like a

Yeah, that looks like a pretty good place to start.

 

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I strongly recommend against

I strongly recommend against just randomly swapping chips. While there is a small chance you may accidentally get the second computer running, there is an equal possibility of damaging ICs from the donor computer. 

First verify the following:

Are your power supply voltages *measured on the motherboard* within 10% of what is expected?

Do you have a running oscillator? Are your clock signals present at the CPU? Bonus if you can measure the frequency.

Is the CPU getting a reset signal? No CPU reset, no code execution.

The other reason I do *NOT* just recommend just chip swapping a //e is that my #1 repair on a //e has *always* been bad sockets. Apple used the lowest quality Cambion single wipe sockets, sometimes mixed with mediocre dual wipe sockets. Any single wipe socket on a //e should be a candidate for replacement. 

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Interesting.  I haven't seen

Interesting.  I haven't seen any socket failures on any IIe, but lots of RAM failures.

 

If you power up and have no video, then the first thing to check is if you have a clock signal.

 

 

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baldrick wrote:Interesting.
baldrick wrote:

Interesting.  I haven't seen any socket failures on any IIe, but lots of RAM failures.

 

If you power up and have no video, then the first thing to check is if you have a clock signal.

 

 

I had another //e which had both the CPU and MMU sockets fail.  After replacing the sockets and the missing CPU and MMU  chips it is now 100% fully functional.  The sockets Apple used do indeed seem to be of poor quality.  It is possible that someone did an aggressive job of removing and/or inserting chips into that board, but good quality sockets will normally tolerate that a few times at least.  Crappy sockets will often get flaky or completely bad after only a few removal/insertion even if they are carefully done.

 

 

FWIW, I haven't had time yet to drag my oscilloscope out to check the clock for activity on this other //e board mentioned in this thread.  It isn't a huge priority since I have a number of working //e units.  My next task is testing the write for .DSK on VIBR's disk emulator.

 

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