• Please review our updated Terms and Rules here

Commodore 8250LP drive won't format

Z

zippysticks

Veteran Member
Joined
Nov 21, 2017
Messages
575
Location
UK, South East
Hi everyone

Drive 0 won't format but does seem to read and write correctly on a disk formatted in drive 1.
Drive 1 does everything correctly so I assume a problem is with the drive 0 mechanism rather than the control logic.

The format process starts but the head does not seem to step through the tracks and eventually errors with 21, read error,78,01,0.
None of the data on the disk is modified as a result so it seems the format never actually gets started.

Any ideas please ?

Thanks
 
Have you cleaned the heads and checked the speed ?

If you have then likely the top head is faulty…
 
Hello, the LP drives (if I remember there are Panasonic drives in it) suffer from leaking capacitors.

Dave Curran has done a good job documenting the replacement:
blog.tynemouthsoftware.co.uk

Commodore 8250LP Repair

The top of my Commodore wish list was dominated by the final iteration of the PET / CBM machines, the 8296, the SFD-1001 single IEEE-488 dis...
blog.tynemouthsoftware.co.uk blog.tynemouthsoftware.co.uk

If you didn't already, I recommend you replace the power inlet filter as well. Depending on the parts used inside they blow up like RIFA capacitors.
 
One other bit of help .. have you replaced the capacitors on the drive boards ? If not you must as they will leak.

There is a much better link from this website on how to dismantle the drive and replace the caps. I have refurbished 3 units and found the same issue as you with one of them but leaky caps on most of them. Use google translate option to get it into English.

forum.classic-computing.de

Auslaufende Elkos in CBM 8250lp / SFD 1001 / CBM 8296d - VzEkC e. V.

Vor wenigen Tagen habe ich an der Motorplatine eines Matsushita JU-570-2 Diskettenlauferks Korrosionsschäden durch auslaufende Elkos festgestellt.Die betroffenen Elkos haben eine schwarze Hülle. Das aufgedruckte Logo dürfte von Mitsubishi sein.Dieser…
forum.classic-computing.de forum.classic-computing.de
 
Last edited:
I was unable to fix the format issue on one of my drives as the upper head was faulty and converted the drive to a 8050
 
If drive 0 does really read and write correctly (with a disk formatted from drive 1) then the read/write heads must be OK.

I would check the sector pulse, write protect and track zero sensor signals from drive 0 first; then look at the tachometer (speed signal) - if it is fitted; and finally the erase head.

The technical manual describes the resistances of the various head windings (erase and read/write), so this should be a simple thing to check with a multimeter.

If the erase head has gone (or the circuitry driving it has gone) west, then this may be your root cause?

Dave
 
daver2 said:
If drive 0 does really read and write correctly (with a disk formatted from drive 1) then the read/write heads must be OK.

I would check the sector pulse, write protect and track zero sensor signals from drive 0 first; then look at the tachometer (speed signal) - if it is fitted; and finally the erase head.

The technical manual describes the resistances of the various head windings (erase and read/write), so this should be a simple thing to check with a multimeter.

If the erase head has gone (or the circuitry driving it has gone) west, then this may be your root cause?

Dave
Click to expand...
Don’t quite follow Dave. The read write heads can read a floppy but the 8250 is double sided so you may not be exercising the upper head and using the lower head. That’s why it can be configured as a 8050 The first thing as a must is to replace the caps and then check the speeds using the dial tools downloadable from zimmers.net as well as check the resistances as you pointed out. It’s a common reported issue with this drive.
 
That is why I queried whether it does really read and write correctly. If it is a 'simple' test and is not exercising the upper head - then that is not (in my mind) a thorough test (testing both read/write heads)...

Before wielding a soldering iron - you should always obtain as much information from the patient as possible first.

All you are saying to do is to replace the capacitors first. All I am saying is to do the tests first...

Dave
 
Dave, …. changing the caps is a must as they are certain to leak … which can also cause issues with the drive. Sorting that first by following the procedure outlined in the link I provided is the first cause of action in my humble opinion…. There are many occasions where it breaks tracks due to leakage. Formatting disks on the LP is very speed sensitive also …

Doing anything else maybe useful .. but limited value until you check for cap leakage on those drives …
 
Last edited:
The diagnostic program for the 8250lp also tests both heads … it’s in the 8296d diagnostic image. not by laptop to find the link. The program will show speed so you can adjust and also then you can do a radial alignment check for both heads
 
AndyG said:
The diagnostic program for the 8250lp also tests both heads … it’s in the 8296d diagnostic image. not by laptop to find the link. The program will show speed so you can adjust and also then you can do a radial alignment check for both heads
Click to expand...
Sorry Andy, do you have an image of floppy disk with the diagnostic program for 8250lp drive?
 
You must log in or register to reply here.
Back
Top