FD400 drive troubleshooting

Allison ajp166 at bellatlantic.net
Thu Nov 22 08:24:31 CST 2007

>Subject: FD400 drive troubleshooting
>   From: "Richard A. Cini" <rcini at optonline.net>
>   Date: Wed, 21 Nov 2007 19:54:46 -0500
>     To: "Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>    As you all know from previous posts, I¹m having trouble with the drive
>system on my IMSAI. While I wait to receive a memory board and some other
>stuff from a friend of mine, Herb Johnson gave me some new energy in looking
>at the existing iCOM Frugal Floppy system.
>    This system uses Pertec FD400 drives. One works perfectly, the other one
>has consistent CRC errors as evidenced by the CRC light on the drive
>cabinet, and BDOS errors reported by CP/M. I ensured that the spindle is
>engaging the diskette hub, and I also cleaned the heads using a wet cleaning

Get in there and scrub the head with a swab.  I found the wet disks didn't 
cut it long ago.

Make sure the spindle speed is good and not irregular.

Try swapping drives A and B and se if the problem moves with the drive 
or not.  Just to make sure you not having a issues with something else.

>    Is there any common failure mode on this model of drive that I should
>start tracking down?

Everyone I'd seen either had fallen apart mechanically (broken hubs,
doors or other plastic) or the drive motor had gone noisy or mechanically
flakey.  NOTE: those motors often had bronze (oilite) bearings that dried 
out and then became oval or other wise out of useful shape. It was a side
effect of lot of hours and the belts side tension. Result is the motor
speed is uneven.  I've seen bad boards too, usually tossed the board and
salvaged from another mechanical pig.

> I looked over the maintenance procedures for the drive
>and many if the tests allude to a diagnostics program that can manually
>control the spindle and head stepping. None of the iCOM manuals I have
>provide diagnostics code for manually controlling the drives in this manner..

There maybe diags but your on you own to find them.

>    Before I start coding, does anyone have diagnostics code I can use? I
>found some code in the SIGM archive (for the iCOM 3712 controller) but it
>doesn¹t seem to work properly with this controller.

What controller (CHIP on the FDC board)?


>    Thanks.
>Rich Cini
>Collector of Classic Computers
>Build Master and lead engineer, Altair32 Emulator

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