Commodore 8050 won't format -> bad disk (?)

[GanjaTron]

Hi everyone, hope you all got the year off to a good start.

I have a CBM 8032 which has been in storage in my basement for aeons, along its 8050 dual floppy. I decided to finally check it out over the Xmas break as I ran into issues with the Big Bad Blue Mallory 27000 µF filter cap in my 2001, and I figured I should check the caps in my other PETs and floppies before placing an order for spares -- shipping to Europe is insane these days!

I never tried the 8050 before, but I do have a 4040 on my CBM 3032 which works without issues, so I had high hopes. The 8050 passes initial powerup with a green status LED, so I figure the digital board is ok, and I initially (and naively) expected no further problems. Haha.

The 8050 has DOS 2.5 in ROM and uses Micropolis 1006 drives. TBH not the best mechs I've seen, and I found the "tethered" setup with drive 1 dangling from drive 0's analogue board via very short cables to be a major pain when adjusting and troubleshooting.

Since I have no preformatted disks, I tried to format a spare DS/DD disk using the BASIC 4.0 "header" command. Both drives bump with a loud jarring noise and give up after a few seconds, but the status LED remains green. BASIC returns a "bad disk" error, but when I print ds$ I get "21,read error". Is the drive checking the formatted tracks on the fly?

Things I tried so far:

• The 5V and 12V supply voltages and ripple are within spec
• I checked the disks mechanically, and found that drive 1 has major resistance on the stepper lead screw, and it makes a rumbling or "groaning" sound when seeking. The grease on the lead screw wasn't really hard but gunky, so I cleaned and relubed that on both drives, but there's still more resistance on drive 1, even after I ran a drop of oil down the stepper motor shaft. At this point I don't know whether it's the motor itself or the head carriage, and I'm hesitant to dismantle the thing as I'll then probably have to realign the drive -- without any reference disks.
• Lastly, I checked the spindle motor using the strobe method on both drives; they were basically spot on.
• The belts are a tad sloppy, but not to the point where they lose grip. That said, I'm not ruling out some slip. I suppose this could be checked via the indexing pulse period.

I've gone through some of the other posts on the 8050 here, but none seemed to resolve or address the issue. So short of breaking out the scope and poking around on the analogue board, I wanted to check if anyone has further hints I can try.

Many thanks and have a good weekend,

--Roland

 

[powerlot]

Pround owner of this monstrosity here... did you lube the worm drive? When I restored mine I noticed that the grease was completely solid.

Before first power up I dropped quite an amount of solvent on the grease and turned the worm drive manually back and forth until it felt right. If you have silicone grease (or any grease that doesn't attack plastics) you can also completely clean it and reapply some fresh one

 

[GanjaTron]

Pround owner of this monstrosity here... did you lube the worm drive? When I restored mine I noticed that the grease was completely solid.

Before first power up I dropped quite an amount of solvent on the grease and turned the worm drive manually back and forth until it felt right. If you have silicone grease (or any grease that doesn't attack plastics) you can also completely clean it and reapply some fresh one

Hi Powerlot, thanks for the quick reply.

Yeah, there's a reason they call these "boat anchor" drives.

I cleaned the worm drive on both mechs and, after not finding silicone grease (I swore I had a tube of that stuff somewhere), I fell back to teflon spray, which should be safe for plastics and rubber too. Again, drive 1 is noticeably stiffer, so I figure it's the stepper motor, whereas drive 0 runs smoothly and is quieter. Still, both drives throw the same error, which is why I figure there's an issue with the shared analogue board.

I might add I checked the two electrolytics on the analogue board, which still measure good. I noticed a few tantalums on there too, so I'll check those next. The head load pads on both drives don't really look too bad, though they should probably be replaced. Applying light pressure on them during formatting seems to have no effect.

I dunno how many hours this drive has seen, but both it and the 8032 are actually in really good shape. Little sign of use and no smudges from grubby hands. Ok, the 8032 keyboard is a bit grimy. and could use a wash.

--Roland

 

[powerlot]

It really is a boat anchor!

One thing to check before breaking out the scope is that the connectors are deoxidised and also verify that the heads are connected the right way.

On mine they cross, means the left drive's head connector goes on the right connector on the logic board. I made that mistake and was wondering why both drives don't read (duh).

 

[GanjaTron]

Hi Powerlot,

the connectors are remarkably clean in this drive. Infact, the whole drive looks almost pristine apart from some dust. And I can confirm the head connectors do indeed cross (which kinda irritated me at first, but it's in the service manual too). Btw, those flying LED leads running across the drives drive (pardon the pun) me nuts!

 

[powerlot]

Well, then it's going to be a bit more of a challenge! Let me know if I can verify something for you on my working drive if the service manual stops being helpful...

 

[GanjaTron]

Yeah, appearances can be deceiving, eh? I guess I'm gonna start with the head amps (I think there's some test points to adjust the "cat eyes") and work my way back. Thanks for your support, will buzz you if I need some checks on a known good drive.