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From: rajah@ohstpy.mps.ohio-state.edu
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Spurious "Disk is Write Protected"
Message-ID: <9688.27e3dc02@ohstpy.mps.ohio-state.edu>
Date: 18 Mar 91 02:13:38 GMT
References: <103405@unix.cis.pitt.edu> <9675.27e10c98@ohstpy.mps.ohio-state.edu>
Lines: 57

In article <9675.27e10c98@ohstpy.mps.ohio-state.edu>, rajah@ohstpy.mps.ohio-state.edu writes:
> In article <103405@unix.cis.pitt.edu>, djbpitt@unix.cis.pitt.edu (David J Birnbaum) writes:
>> My 5-1/4" 1.2M floppy drive has been refusing to write to diskettes,
>> telling me that the "Disk is Write Protected."  This problem ......
>> 
>> The diskettes are all high quality and formatted normally.  There is no
>> visible dust or debris inside the drive in question.
>> 
>> Is this a known problem?  Is it one I can repair by myself and, if so,
>> how?  Given the bargain basement prices of disk drives, it hardly seems
>> worth getting it repaired professionally, but if all it needs is some
>> particular cleaning in some particular place, I'd be grateful if some-
>> one could let me know.
>> 
>> Thanks,
>> 
>> David
>> 
>> =======================================================================
>> Professor David J. Birnbaum         djbpitt@vms.cis.pitt.edu [Internet]
>> The Royal York Apartments, #802     djbpitt@pittvms.bitnet   [Bitnet]
>> 3955 Bigelow Boulevard              voice: 1-412-687-4653
>> Pittsburgh, PA  15123  USA          fax:   1-412-624-9714
> 
>   we experience the same problem with a computer in our lab. Drive "A"
>   simply refuse to write. But it can copy from drive "A" into "C" or 
>   into memory. So no problem with the media (disk). I guess the drive 
>   somehow feels there is a protection tab on the disk. Probably the tab
>   sensor does not move freely. We are going to check it soon. Any other 
>   suggestion on this is appreciated. Thanks,
> 
>   Rajah.
> 

    As soon as I opened up the drive realized the sensing of tab is 
    done by optical means----source:an LED, detector: a photodiode.

    This information is also mentioned by Mr. Quimby and Mr. Terje. Thanks.

    On testing (experimenting) found the followings:

    1. Cleaning dust didn't help.
    2. Unpluged the photodiode(detector) as it was easy to remove and 
       did the diode test. Test passed.So photodiode ok.
    3. LED wasn't easy to check as it is soldered to the PCB. However, 
       found a short cut. Issued the fomat command without the photodiode 
       in place....hoping to see light from LED. No light from LED. 
       So bad LED.

    4. Proof: Shine light on the photodiode with a flash light while 
       issuing format command. It started formating. As shining light 
       on photodiode is disrupted formating stoped with an error message.

    Now I need to replace the LED. Could anyone help me with the 
    specification and the place where I could buy this LED. Thanks very much.

Regards.