Commodore 1541 drive can't format or read disks

[FlightDeck]

Hi everyone! :smile:

I'm working on a Commodore 1541 drive that I took out of storage after about 30 yrs (in original box). It won't read or format any disks. Looking for suggestions or how I can diagnose it. I don't have access to an oscilloscope at home, so any suggestions about how I can test it without one would be great. I also don't have another drive so I can't load any test programs.

Details below...

- Connected to a 64C.
- Newtronics type with the spin lever and "long" mainboard (photo). It's a "1542" mainboard #250446 (or "1541 A-2").
- All power-up behaviour seems normal (light sequence, motor, etc.)
- Can't format disks. Shortly after the initial rattle to position the head at the first track it stops with no error on screen, and the red drive light is flashing. The drive error code is 21 READ ERROR 0 0.
- Can't read disks. The first attempt to load the directory of any disk does not move the head from track 18 (if it's already there), the screen says FILE NOT FOUND, and the error on the drive is 74 DRIVE NOT READY 0 0. On any subsequent attempts for a disk, the head will try track 18, then bump to the stop and back to track 18, the screen will say FILE NOT FOUND, and the drive error is 20 READ ERROR 18 1.
- Cleaned the head (it had very little dirt on it).
- Drive spins disks okay.
- Confirmed the head can move to all tracks (used a BASIC program to manually step the head in and out).
- Confirmed continuity of the head at the black connector to the mainboard.
- Checked resistance on head wires, all reasonable (blue-black 12 ohm, blue-yellow 25, blue red 25, black-yellow 14, black-red 14, yellow-red 27), no open/short. (Note pin 1 blue, 2 black, 3 yellow, 4 empty, 5 red.)
- Swapped VIA 6522 UC2 and UC3 chips and no change.
- Checked pretty much every mainboard trace for continuity according to wiring diagram.
- Tried a second serial cable, no change.
- I've been using the SAMS/Peltier 1541 troubleshooting guide. The simple flowchart points me to "read/write circuit" in the detailed flowchart. I can only do a few steps before it requires an oscilloscope, which I don't have at home.
- I've also been through every forum post, Ray Carlsen guide, etc. that I can find, but they don't help pin down how to find the problem (other than just replacing every chip until it works again?).

From the above I conclude:
- Something preventing it from reading anything.
- Alignment isn't the (primary) problem, since it can't format.
- Head is okay.
- UC2 and UC3 VIA chips okay.
- Power circuit okay.
- Head and disk motors and drive mechs all okay.


Many thanks!

 

[Ruud]

What I do in such cases is taking out a second drive and start swapping parts, starting with the complete board. If you don't have one, consider buying a second one. IMHO it should be cheaper than buying a scope. And a second drive comes in handy when you need to copy disks: much faster and no need to swap the disks every few seconds.

Success with your repair!

 

[VintageVic]

I agree with Ruud, second working drive makes the job easier. You could then easily try pcb on
a working mechanics and rule out if it is a proble with mechanics or pcb.

Yet there is some things I can suggest. If the drive has not been messed with, it might not be alignment issue.
But it could be issue with spinning speed.

I had one mechanics that had problem keeping the disc tight enough in the grip. When the disc sounded spinning,
it actually was not spinning at all, but it was slipping there. Check that your disc is actually spinning (I had this issue with 1541-II drive mitsumi mechanics).

Secondly, if the bearing is very dirty or the grease is old/sticky that could give drag to the spinning speed. Optimal spinning speed is 300rpm.
you probably can read discs still at 298rpm, but lower than that it starts to be difficult and you will start to see read error issues. Open
that spindle rotator (or what every you might call it), clean from old dirt and grease and give it some fresh lube. Be careful with spings they might
fly away when you open it. And finally assemble back in backwards order. Clean well all surfaces that hold the disc in the rotator before reassembly.

 

[ldkraemer]

What is the Device Number of the Drive? 8, 9, 10, 11 ??

After you format the Floppy, Did you Initialize it? What was the Read Error?


Send me a PM with your email address. I have a PDF manual you will want.


Larry

 

[rittwage]

I know you said you tested it, but the heads on Newtronics/Mitsumi drives are usually dead now. I have stacks of them, and this is the same exact behavior to a dead coil.

Make sure when you were measuring, a "K" did not appear. It's easy to see one come up 14ohms, and the next is 14K and you don't notice. They will be very high resistance, but not usually open. There is a 15k resistor in parallel with some coils.

 

[iz8dwf]

I know you said you tested it, but the heads on Newtronics/Mitsumi drives are usually dead now. I have stacks of them, and this is the same exact behavior to a dead coil.

Make sure when you were measuring, a "K" did not appear. It's easy to see one come up 14ohms, and the next is 14K and you don't notice. They will be very high resistance, but not usually open. There is a 15k resistor in parallel with some coils.

well, In the last two years I've repaired at least 10 x 1541 with Newtronics mechanical assembly and I've found only one with failed head.
An analog problem can be easily spotted with an oscilloscope. It can be one of the amplifiers (NE592), it can be the comparator (LM311) , even a bad transistor or a bad 7417 or even a bad gate array.
To fix things, one must try to understand how they work and have a way to check what is instead not working.

Frank IZ8DWF

 

[VintageVic]

I think you have been lucky, Frank.

Just like Rittwage, I also have a fair pile of failed mitsumi mechanics with a dead head.
I haven't really made good statistics, but I'd say a good half of the failed drives with mitsumi mechanics
that I've come across have had the dead head. First thing on my mind was therefore also the head,
but since the head has been measured and the resistance between wires seems to be ok, I'd
be willing to give this unit a chance of having good head.

Strangely, most of the open heads have resistance of about 15 kilo-ohms between some of the wires
in my experience.

 

[FlightDeck]

Hi everyone, many thanks for all the replies!

In the time since my first post I've removed, cleaned, and reinstalled all of the socketed chips' pins and sockets (previously UC2 and UC3, and now also UC4, UB3, and UB4). Found some dirt on a few pins, but still no change from before.

I agree with Ruud, second working drive makes the job easier.

Check that your disc is actually spinning (I had this issue with 1541-II drive mitsumi mechanics).

Secondly, if the bearing is very dirty or the grease is old/sticky that could give drag to the spinning speed. Optimal spinning speed is 300rpm.
you probably can read discs still at 298rpm, but lower than that it starts to be difficult and you will start to see read error issues. Open
that spindle rotator (or what every you might call it), clean from old dirt and grease and give it some fresh lube. Be careful with spings they might
fly away when you open it. And finally assemble back in backwards order. Clean well all surfaces that hold the disc in the rotator before reassembly.

A second drive is not in the cards. I was only checking this drive to verify it still worked okay so I could find a new home for it. Was actually caught by surprise that it wouldn't read or format anything. I thought maybe it would be something simple wrong with it that I could fix, but poking at it all week I think there's not much I can do with it.

As mentioned the disks are spinning okay. I don't know their exact speed though. I haven't opened the bearing, could maybe try that this weekend.

What is the Device Number of the Drive? 8, 9, 10, 11 ??

After you format the Floppy, Did you Initialize it? What was the Read Error?

It's 8. Initialize also gives error. I get 20/21 READ ERROR 18 0/1, depending on what I did just before the Initialize (load directory or format attempt) and whether the disk has data or is a blank I'm trying to format.

I know you said you tested it, but the heads on Newtronics/Mitsumi drives are usually dead now. I have stacks of them, and this is the same exact behavior to a dead coil.

Make sure when you were measuring, a "K" did not appear. It's easy to see one come up 14ohms, and the next is 14K and you don't notice. They will be very high resistance, but not usually open. There is a 15k resistor in parallel with some coils.

I've checked several times (2 different multimeters) and confirmed the resistance measurements in my first post. Nothing even close to kohm range.

An analog problem can be easily spotted with an oscilloscope. It can be one of the amplifiers (NE592), it can be the comparator (LM311) , even a bad transistor or a bad 7417 or even a bad gate array.
To fix things, one must try to understand how they work and have a way to check what is instead not working.

Yes, this is why I'm asking if there are alternative ways to check if a chip is good that doesn't require an oscilloscope. The lab I work at has that equipment, but we haven't been there for a year now because of CV19, and this unfortunately doesn't pass the "essential services" test for me to visit there So I only have multimeter at home.

If I was at work I could use the oscilloscope to run the full detailed flowchart in the SAMS troubleshooting guide to check all the components. Could also Xray to look for defects on the PCB or in the chips. But it'll be a long time before we go back there (probably 2022)


Thanks again

 

[ZappedC64]

Yes, this is why I'm asking if there are alternative ways to check if a chip is good that doesn't require an oscilloscope. The lab I work at has that equipment, but we haven't been there for a year now because of CV19, and this unfortunately doesn't pass the "essential services" test for me to visit there So I only have multimeter at home.

If I was at work I could use the oscilloscope to run the full detailed flowchart in the SAMS troubleshooting guide to check all the components. Could also Xray to look for defects on the PCB or in the chips. But it'll be a long time before we go back there (probably 2022)

It's not exactly cheap, but Evie has created a new chip tester. It does support in-circuit testing as well. I got one a few weeks ago and absolutely love it!

https://store.backbit.io/product/chip-tester/

 

[FlightDeck]

It's not exactly cheap, but Evie has created a new chip tester. It does support in-circuit testing as well. I got one a few weeks ago and absolutely love it!

https://store.backbit.io/product/chip-tester/

Haha yeah I was drooling over that last week! :D Looks like a sweet rig! Sadly it probably means spending more than the drive is worth even if I can fix it.


So this weekend I removed, cleaned, and serviced the disk spindle (the upper idler spindle, not the lower one driven by the motor). The grease didn't look so great, so I completely disassembled, cleaned, and re-lubed it. Also lubed the head slide rails while at it. Made no difference though, still won't read or format any disks

If anyone is interested for future reference, here are photos of the upper spindle: before disassembly and after disassembly/cleaning.


Also re-ran some read and format tests. For clarity, here are the errors. The only difference between a disk with data and a blank disk is error code 21 vs 20.

Function	Data disk	Blank
Load $ (first time)	74 DRIVE NOT READY 0 0	74 DRIVE NOT READY 0 0
Load $ (subsequent times)	20 READ ERROR 18 1	21 READ ERROR 18 1
Initialize	20 READ ERROR 18 0	21 READ ERROR 18 0
Format	N/A	21 READ ERROR 0 0

That 74 error the first time on every disk still seems to point to a hardware issue somewhere on the mainboard.


Cheers

 

[JoeBliksem]

Also re-ran some read and format tests. For clarity, here are the errors. The only difference between a disk with data and a blank disk is error code 21 vs 20.

Function	Data disk	Blank
Load $ (first time)	74 DRIVE NOT READY 0 0	74 DRIVE NOT READY 0 0
Load $ (subsequent times)	20 READ ERROR 18 1	21 READ ERROR 18 1
Initialize	20 READ ERROR 18 0	21 READ ERROR 18 0
Format	N/A	21 READ ERROR 0 0

Hi there - I am experiencing exactly the same symptoms with a (Newtronics) 1541 I got from ebay. You haven't perhaps solved this in the mean time?

Cheers
Joe

 

[BennehBoy]

If the head resistances check out then Frank's post above is spot on for the parts that could be at fault, it's scope time, or substitution with known good parts to address.

Similar issues I've seen on 2 Alps drives were a failed gate array in one instance, and failed 592 in the other.

 

[JoeBliksem]

If the head resistances check out then Frank's post above is spot on for the parts that could be at fault, it's scope time, or substitution with known good parts to address.

Similar issues I've seen on 2 Alps drives were a failed gate array in one instance, and failed 592 in the other.

Had another more thorough look at head resistances. Red -> any other fails. I guess it's dead? Boy these things really are ticking time bombs?