nikola-wan
Veteran Member
I've made progress on both my 4907 Floppy drive systems- memory errors during boot have been fixed - 2 bad 4027 DRAMs on one and I replaced five 4027 on the other - more difficult on the second one because they were soldered in, so I had to remove the ceramic DRAMs and install sockets.
Both systems now run the 4907 operators manual example BASIC program for the Tektronix 405x computers to set the time - but both fail to access the floppy disk with Error 16.
The 4907 service manual downloaded from bitsavers indicates the following items for this error:
I have connected my HP 1630A logic analyzer probes to the pins in the ribbon cable between the mainboard and the ROM board - and when I trigger on a read of the hex address 4014 RP0 status register - I see the drive reporting not ready.
Ok, download the Shugart 800/801 Floppy Drive service manual. That manual indicates that the drive is looking for sector pulses from the sensor above the disk and the door closed sensor before reporting drive ready.
Ah-hah - my 8" NOS disks are double-density double-sided - and the disk hole is offset from the sensor on the 800 floppy.
More google searches turned up the reason for the disk not ready:
https://groups.google.com/d/msg/comp.os.cpm/NqpeHqaAeqQ/aQ4QpNsF-g8J
I don't have the right floppy - I need a single sided single density hard sectored floppy: SSSD, the DSDD floppies I bought won't work.
These SSSD floppies have 32 sector holes and an extra hole to indicate first sector - see 3M floppy disk manual on bitsavers:
http://www.bitsavers.org/pdf/3M/3M_Diskette_Reference_Manual_May83.pdf
The 4907 Service Manual shows the mainboard logic has a sector counter - and requires the 32 sector holes.
I've ordered a box of 8" SSSD Nashua floppy disks - EBAY seller indicated they have lots of holes - and the location of the sensor hole matches the one on the 4907 drive (7 degrees from the center line through the slot for the head)
I'll hold my breath until I get these floppies next Friday.
Both systems now run the 4907 operators manual example BASIC program for the Tektronix 405x computers to set the time - but both fail to access the floppy disk with Error 16.
The 4907 service manual downloaded from bitsavers indicates the following items for this error:
I have connected my HP 1630A logic analyzer probes to the pins in the ribbon cable between the mainboard and the ROM board - and when I trigger on a read of the hex address 4014 RP0 status register - I see the drive reporting not ready.
Ok, download the Shugart 800/801 Floppy Drive service manual. That manual indicates that the drive is looking for sector pulses from the sensor above the disk and the door closed sensor before reporting drive ready.
Ah-hah - my 8" NOS disks are double-density double-sided - and the disk hole is offset from the sensor on the 800 floppy.
More google searches turned up the reason for the disk not ready:
https://groups.google.com/d/msg/comp.os.cpm/NqpeHqaAeqQ/aQ4QpNsF-g8J
I don't have the right floppy - I need a single sided single density hard sectored floppy: SSSD, the DSDD floppies I bought won't work.
These SSSD floppies have 32 sector holes and an extra hole to indicate first sector - see 3M floppy disk manual on bitsavers:
http://www.bitsavers.org/pdf/3M/3M_Diskette_Reference_Manual_May83.pdf
The 4907 Service Manual shows the mainboard logic has a sector counter - and requires the 32 sector holes.
I've ordered a box of 8" SSSD Nashua floppy disks - EBAY seller indicated they have lots of holes - and the location of the sensor hole matches the one on the 4907 drive (7 degrees from the center line through the slot for the head)
I'll hold my breath until I get these floppies next Friday.
Last edited: