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SE FDHD Floppy Transistor

danny.gonzalez.0861@gmai

Well-known member
Hello everyone,

I recently purchased my second SE FDHD for $45 + shipping on the fleebay (Yes I have a problem). It had a dead tube but I had one laying around hence why I bought it. After replacing the tube I tried to test the rest of the machine and noticed the floppy drive continuously runs the eject motor. I swapped in my floppy from my IIci since it's easier than taking apart my other SE FDHD and it boots like a champ. I decided to tear into the defective floppy drive to see why the motor constantly ran thinking it was the common bad gear. Well it was the gear as it was stripped but upon replacing it, I noticed that didn't fix the issue, motor still runs continuously. Next I opened the position switch and unfortunately continuity checked out as expected meaning the switch is working. Next I started to look at suspect component to which I found none visually but once I started to test continuity, I realized Q9 is shorted. Here in lies my issue, Q9 is marked B.7 but I can't find a correct replacement.

Q4 which also says B.7 is not shorted in the same manor and my IIci drive says Bv4 for those transitions so needless to say I am absolutely lost.

Can someone please please please tell me what part I can purchase to get this floppy working again?

Here is a photo of the transition in question. (See attached)

Any help will be greatly appreciated!!

Thanks!
 

Attachments

  • PXL_20240527_014438550.jpg
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codevonlux

Well-known member
Refer to the schematic:

It is not exactly the same model but from your symptom and PCB trace photo it should match Q7 in the attached schematic: 2SB624-BV4. It is responsible to provide 12V to the eject motor upon control from the controller. If it is shorter then eject motor will be always fed 12V without control.
 

Attachments

  • 800K DRIVE.pdf
    110.7 KB · Views: 12

danny.gonzalez.0861@gmai

Well-known member
Refer to the schematic:

It is not exactly the same model but from your symptom and PCB trace photo it should match Q7 in the attached schematic: 2SB624-BV4. It is responsible to provide 12V to the eject motor upon control from the controller. If it is shorter then eject motor will be always fed 12V without control.
Thanks for the response and schematic! I have ordered the part and will inform if it worked :)
 

lmartu

Well-known member
Did it work? I have the exact opposite problem on a high density drive. The motor does not eject , but works perfectly on another drive !
 

danny.gonzalez.0861@gmai

Well-known member
Hey Imartu,

This second SE FDHD of mine is straight out of HELL! I got the Transistors and when I went to test the drive my Flyback shorted out and I didn't want to damage anything else so I left it there in the bench with my ego lol. When I get home tonight I will test the drive with my original SE FDHD which has been working perfectly and I will let you know.

Just needed to walk away from the disaster of the bad Flyback and collect my thoughts.
 

LaPorta

Well-known member
That schematic is awesome! I needed that something like three years ago. Where were you then??
 

codevonlux

Well-known member
I just jumped into this vintage macintosh business in 2024, before that I was never exposed to anything before late in the PowerPC era.
 

codevonlux

Well-known member
There're many variations for 800K 51W but the common circuits around eject mechanism, power-saving switch for 5V(C) and 12V(C), Stepping motor control remain the same even in later FDHD drives.
 
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