[vcf-midatlantic] OSI Floppy diagnostics

[Bill Dromgoole]

Dave, thanks for the OSI 
drive test program.
I started on a Tandon 848-2 drive with no data separator.
I am using an external separator.
I had it working at one time. But it stopped for some reason.
Using the disk test option 1 , I got so many errors I thought it wasn’t even writing.
But, not really understanding your program, I decided to try it on my good drive that boots into OS65 all the time.
The first disk I tried had maybe two errors out at track 75,76.
Next two disks I tried looked like the Tandon did.
Went back to the disk with only two errors and it was just like the Tandon. Full of errors like -1600 or so on each track.
Now it will no longer boot with a good disk.

I can only guess that some of the disks that I tried dirtied up the read head on the drive and more than likely is the reason the Tandon stopped working also.
Tomorrow I will take out the drive and clean the head and see where I am.

I like being able to see the status and move the head to different tracks, it give a lot of confidence that the drives are basically working.
I haven’t tried scope mode yet but I can see how valuable it is.

I do have a question about the 3.0 microSecond delay.
The siemens drive manual say to set the data separator pulse to 2.75 microSeconds
And several other sources like the Dragon Byte technical manual(attached) says to use 2.5 micro Seconds.
My controllers are set at 2.5 and all seem to work.
Although 125 Kilohertz clock on five inch drives uses a 6.0 pulse
So I guess a 250 Kilohertz clock would use 3.0, it kind of makes sense.

What do you think, should I realign everything to 3.0 pulse width?


From: David Gesswein via vcf-midatlantic
Sent: Saturday, May 16, 2020 3:35 PM
To: vcf-midatlantic at lists.vcfed.org
Cc: David Gesswein
Subject: [vcf-midatlantic] OSI Floppy diagnostics

At the last workshop my machine was having problems with B drive and
two other OSI machines people brought the floppy drives weren't working at all.

I didn't find any floppy diagnostics for the OSI so I wrote on.
http://www.pdp8online.com/osi/osi-floppy-test.shtml

With some floppy testing info here
http://www.pdp8online.com/osi/floppy-repair.shtml

If you try it let me know how it goes.

Bill got his machine working before I finished this. Jeff, hows your machine
doing?