Disk II Floppy Drive Missing RF Shield

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Disk II Floppy Drive Missing RF Shield

Hi All,

I recenty got a three Apple Disk II 5.25 drives (AM2M0003).  I noticed that one drive has an RF shield inside and the other two drives have the RF shield missing.  I'm wondering if it's missing because someone took it out and forgot to put it back in, or was this something that was added/removed as some point in production at the factory.

The one with the shield intact has never had it's internal screws removed, while the other two with the missing shield show signs of screws being removed for servicing.  So my hunch is that someone took the shields out perhaps?

Can someone please confirm if all drives are supposed to have these?

It looks like the aluminum shield is there to protect the logic board from interfering with the read/write head located under it.

 

 

CVT
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Adrian's doesn't have one:

Adrian's doesn't have one:

 

https://youtu.be/ukvT7131pRU?t=1157

 

and neither does mine:

 

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I doubt anyone would remove

I doubt anyone would remove it.  I don't think early drives had it but I don't know when it was added.  There were several revisions of the Disk ][ over the years, mostly to address RFI issues.  The most visible is the changes to the cables from the early unshielded rainbow ribbons to the later grey ones.  They also used both Shugart SA390 and Alps mechanisms.  There were also some cosmetic (sticker) differences depending on where drives were made.  I've got ones that are USA, Cork, IRL, and Singapore.  There may have been others.

 

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Thank you for confirming I'm

Thank you for confirming I'm not the only one without a shield there.

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It's apparently a production change

From my experience servicing Disk II drives in the school's computer lab, there's a vague correlation between the RF shield and the hole in the analog board.

  • On many (but not all) drives without an RF shield, there's a rectangular opening in the analog board that enables you to access the heads without removing the analog card.  This enables you to clean the heads by lifting the pressure pad and passing a swap through the opening.
  • On drives with an RF shield, the analog board invariably omits the hole.  Apparently Apple didn't see any reason to cut that hole in the circuit board, since you could not access the heads if the RF shield was present.

My best guess is that Apple made these two changes some time around 1982 because the Disk II drives on our Apple ][ J-Plus computers omitted the RF shield and generally had the hole in the analog card, whereas our Apple //e computers all had an RF shield and omitted the hole.

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