Failing DISK II controller

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Failing DISK II controller

Hi

 

I made a mistake, I inserted a disk II controller le wrong way...

several chips burnt... including some on the analogic board of the Disk II drive....

 

the analogic board of the disk II is repaired and works

all the burnt chips on the Disk II controller replaced including the P5 prom  (all are working)

 

the Apple try to boot but the engine never stop and it never read

I tested all chip

(everything works fine with a second controller)

(even if I swap the chips between the good and the failing board)

 

there are no traces of burnt tracks on the board

 

any idea of the failing element ?  perhaps a transistor ?

 

thanks

 

 

 

 

 

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What about the capacitors?

What about the capacitors?

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Aren't there a couple of caps

Wayne has a point there...  aren't there a couple of caps on the Disk II Controller card that might pop if shorted?  Also possibly a resistor that might burn through.  The resistors are easy to check, the caps you'd have to remove from circuit unless they are obviously blown.  It should be possible to look at Q1 with a logic analyser also.

 

CVT
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I would align 2 Apple II slot

I would align 2 Apple II slot pinout diagrams in a 69 position and see what went where. Of particular interest will be the power rail pins. Also I would check the +12V on the motherboard, as it powers the motor of the floppy drive.

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Blown Disk II controller
Wayne wrote:

What about the capacitors?

no traces of burn the capacitor and resitors looks ok

 

I checked what happened when I plugged the board the wrong way

apparently +12V was on +5V

+5 on +12V

and -12 / -5 on A5/A6 (I guess it explain why the prom was blown)

 

Apparently the 2 MPSU51 were connected to +12V instead of  5V

that's why I think they are blown too...

 

the  P5 prom remplaced by a SN74S471 works, the card is recognized

 

I ordered some MPSU51 to replace them

 

no problem with the machine, the machine works fine with another Disk II controler

 

thanks to all

 

 

 

 

 

 

 

 

 

 

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fix found tor broken Disk II controller...

I changed the 2 MPSU51 but no effect

I disconvered that pin 10 the P6 prom was partly broken

I created a sort of "twin" with a cheap chip  a 74LS00

once the broken pin soldered to a pin of the other chip

I cut it from the 74LS00

 

this was the P6 rom can be correctly plugged and the Disk II controller works

in fact the broken pin may have worked for some time

 

thanks to all

 

 

 

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CVT wrote:I would align 2
CVT wrote:

I would align 2 Apple II slot pinout diagrams in a 69 position and see what went where. Of particular interest will be the power rail pins. Also I would check the +12V on the motherboard, as it powers the motor of the floppy drive.

The curious thing for me is, unlike many other cards, the Disk II card when inserted reverse is clearly "odd" as the connectors would be facing the front and toward the PS. That's just odd.

You're right tho and the thing that will cause problems, the flipped card will put 12v on the 5V line and since that's power for everyone... the results are usually pretty bad. I guess they got lucky that none of the ICs did fail, that's crazy! It's usually the first chip in line that takes the damage, something like the 125. Glad they got it figured out!!

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jeff d wrote:CVT wrote:I
jeff d wrote:
CVT wrote:

I would align 2 Apple II slot pinout diagrams in a 69 position and see what went where. Of particular interest will be the power rail pins. Also I would check the +12V on the motherboard, as it powers the motor of the floppy drive.

The curious thing for me is,

Either the motherboard wasn't in the case or this was a ][+ or something, because a Disk ][ Controller card just won't fit into a //e completely backwards like that, the front side is too long.  On a ][+ if it is in a slot that lines up with a V in the back of the case, you could do it I guess.  But it would seem to be super obvious that it was wrong, so I am not sure how it could reasonably happen...

 

 

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