Commodore CBM 8050 Dual Drive Floppy Disk

Once i had finished getting my Commodore PET working i was on the look out for one of these, a Commodore CBM 8050 Dual Drive Floppy Disk. Actually i would have been quite happy with any of the drives available for the PET but i ended up with an 8050. The ebay seller listed it as untested. After an initial inspection i couldn't see anything obviously wrong so i went ahead and powered it up. Sure enough the 3 LEDs flashed in the usual fault indication.

Here's what you see when you first 'pop' the hood. I do love the little bonnet stay on the left.

I tried to insert a floppy disk in each drive, Drive 1 was fine but something was stopping the disk from going onto Drive 0. So i removed the disk drive PCB to get a better look. Straight away you can see that something is amiss, they should look identical but the angle of drive shaft which moves the head is all wrong on Drive 0 (the lefthand drive). After taking the drive out i discovered that the head spindle had come out of the bearing block that it runs in at the far end of it's travel. It was fairly easy to relocate the spindle but i didn't think that the drive would still be able to read the disk as it was probably now misaligned.

After reassembly i could now insert disks into both drives but the LEDs were still indicating a fault. Like the PET a common fault with these drives is the RAM chips. The LEDs indicated a fault with the RAM so i followed the same course of action i used with the PET. Carefully remove the RAM chips and then replace them with sockets, the RAM in the 8050 is 2114, it has 8 of these. Fortunately they are also still available, so i was able to replace all of them and after that the drive powered up correctly with no faults indicated by the LEDs. The picture below indicates the RAM chips.

So did it work? Well amazingly, yes! I tried Drive 1 first as i hoped that it had no physical problems and the PET formatted a disk and then wrote and read to it. Put the same disk in Drive 0 and it read from it! Which pretty much proves that the head alignment is ok.

You can see & hear the drives in action here.

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