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LCII Killed FloppyEMU

max1zzz

Well-known member
I'm working on a battery damaged LCII (well, actually a Performa 400 but it's the same mac, the logicboard is even marked "LCII" :) )

As far as getting the board working it is all going well, the board cleaned up really nicely with some white vinegar and  I ever managed to save the rom chips that I was sure where gonners, you can hardly even tell they where ever corroded now!

So last night I finally washed and tested the board (First with soapy water to get the vinegar and cap goo off, then a 2-3 hour soak in IPA to remove any left over water on the board) and it was looking good, it powered on and initially produced a blank screen I figured this was because of the video adapter I was using (It was one of the ones without dip switches) so I powered down and connected my FloppyEMU, powered back up and the LCII seemed to happily boot the first disk of the 7.1 install set so I powered down again and dug out a adapter with dip switches on, This time when the LCII was powered on I got a good image on the screen however the FloppyEMU was far from happy, it lit up showed the smily face it shows when first powered on and then went blank. Some gentle prodding with my finger showed the CPLD was getting extremely hot and some further probing showed the 3.3v regulator on the board was being pulled down to 1.2v, that's not good! At this point it was gone midnight and I was more than a little annoyed so decided to call it a night.

Today I removed the CPLD from the FloppyEMU board and verified it now powers up and complains the CPLD firmware is incorrect so at least it loos like the rest of the FloppyEMU is OK :) the CPLD chips are £3.05 from Farnell so that isn't too bad either, replacement parts are now on order.

What I can't figure out is what happened to kill the FloppyEMU, I have three theory's that make sense but I'm not entirely convinced by any of them

(1) The LC II board was not totally dry after having been washed, but if this was the case why did it not kill the FloppyEMU the fist time it was connected or on any of the 3 - 4 times I powered the board off and on while trying to get video form the first adapter?

(2) There was something conductive on my desk that shorted the underside of the floppy port on the LCII, I did check the desk before setting the board down but this is always a possibility

(3) The CPLD was bad to begin with and just chose that moment to fail, I did have some issues with another mac not being able to read from the FloppyEMU the one other time I used it however reseating the cable seemed to make that issue go away on the other mac so at the time I assumed it was just that

My plans or the weekend where to finish off this LCII (It needs some jumper wires ran for damaged SCSI traces) and get it reassembled and reinstalled but I am now very cautious about connecting another drive to the mac, although the damage to the FloppyEMU is annoying it should be a relatively simple repair however damaging a original floppy drive will mean tossing that drive in the parts bin as i suspect the controller IC's on those boards will be totally impossible to get now

I'm wondering if anyone has had experience with a mac killing floppy drives (Or FloppyEMUs) and has any idea what I should check?

 

max1zzz

Well-known member
Well at least the floppy Emu is now OK :) Replaced  the CPLD and it's now works fine.

Not sure if I dare plug it back into the LC II though!

 

techknight

Well-known member
There was a blog over on Steves website that went into detail what causes the CPLD to fail. its a known issue. 

 

superjer2000

Well-known member
I thought the issue Steve had noted was just associated with using the floppyemu with th softSp card for Apple iis?  Is there another issue? 

8bitguy replaced his CPLD as he indicated that per Steve, they can just go bad. 

 

max1zzz

Well-known member
https://www.bigmessowires.com/2015/04/19/circuit-protection-economics-and-electronics/ and https://www.bigmessowires.com/2014/03/28/troubleshooting-damaged-chips/ are the blog posts where Steve discusses the issues, but doesn't really come to a conclusion as to the cause of the issue, if you read the comments Steve seems to have had some success in mitigating the issue by placing 1k resistors inline on all the data lines but his testing involved hotplugging which is certainly not what I was doing.

I'll probably never figure out exactly what happened, but it's working now and I ordered a spare CPLD chip so if it happens again in the future (Or it turns out the LCII is really a Floppy EMU killer!) I should be ok

 
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techknight

Well-known member
I think the issue stems from the fact that it is a 3.3V chip. the VCC has to be stabilized before 5V can be applied to any of the I/O pins or it can damage the chip. 

 
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