1571 cannot switch to double-sided mode

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sanvigh
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1571 cannot switch to double-sided mode

Post by sanvigh »

I'd like to ask the Wisdom of the Community a CBM 1571 related question. Here are the details:

The drive:
CBM 1571
255052-03

The Board:
310422 Rev7

What has been Replaced:
PSU: Meanwell PD-25A
U2: JiffyDOS 6.0
U19: >MB74LS241
U14: >SN7407N
U8: >SN7406N

Maintenance done:
Lubricated the moving parts. Checked the conductivity of the heads' wires.

How it functions:
- Turns on and starts spinning. Interestingly the spinning stops even without C64 connected.
- Can read and write(!). I've checked with another drive (OC118 and a 1541-II) that the saved data is readable.
- Cannot format in 1541 mode. The heads move to Track 0 and immediately stops, giving 20,Read error. Note: Only recovers after 2 times querying the drive status with "@"
- Cannot work in 1571 mode. In fact, if I send the command to switch, the green led just starts blinking fast right away.

Update:
I acquired another 1571, which I have not modified in any way and still produces the exact same errors! At this point I tried with different C64, but still the same errors.

The Question:
I've been consulting the great Internet and finding good guides, but the above error is confusing. It should not read...or it at least should format. Why? How to fix this?

So, I humbly ask if anyone has an idea about the next step of troubleshooting.


banman
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Re: 1571 cannot switch to double-sided mode

Post by banman »

Hi sanvigh,


That's a very interesting problem.

Unfortunately I don't own a 1571 disk drive or C128.

Can I ask some questions?

Have you tried formatting an appropriate disk in 1571 mode and then formatting another appropriate disk in 1541 emulation mode?

Can you get access to a C128?

I had lots of problems with actually obtaining the correct floppy disk media for tests on a 1541 drive.
I think the 1541 drives exclusively use DD (Double Density) disks. When I did there were a quite a few that were physically degraded.


Have you had a chance to look at this article....


https://groups.google.com/g/comp.sys.cbm/c/fALaIRfeNS0

A gentleman named Glen P goes into some specific procedures regarding the 1571.

A very interesting read.
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eslapion
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Re: 1571 cannot switch to double-sided mode

Post by eslapion »

sanvigh wrote: Tue Dec 14, 2021 2:41 pm ... I tried with different C64, but still the same errors.
I have a 1571 and use it with both a C64 and a C128 and there is something fishy about your question: Nowhere do you mention trying to use it with a C128 in 128 mode.

Here is how I use my 1571...

On the C128, in fast/80 col. mode, I can insert a blank floppy and it will AUTOMATICALLY be formatted in double sided mode when using the HEADER command.

Using a 1571 drive in double side mode with a C64 or using the C128 in 64 mode requires JiffyDOS. You must use the @N2 command which is only available in JiffyDOS. See page 38 of this PDF: http://www.jbrain.com/pub/cbm/manuals/J ... ble%29.pdf

The 1571 will automatically recognize a floppy formatted in double side mode and switch to the correct mode to use it.

You do mention having the same REMOVED more than one C64 with more than one 1571 drive but don't mention exactly what commands you try to use.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
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Re: 1571 cannot switch to double-sided mode

Post by rmzalbar »

Some thoughts:

- Drive motor should always stop a few seconds after being switched on with no C64 plugged in. There's a pullup on the reset line to ensure it doesn't float low. This is true for 1541 and 1571. You might see the motor run for several seconds if you insert or remove a disk; this is normal for some models, it's a way of helping the hub clamp center properly on the media while you close the latch. It's triggered by the write protect sensor seeing the disk slide in or out.

- Do you have anything else plugged into either the serial chain or into the datasette port?

- Format also fails on the "other" 1571? Or just the commands?

- I see you're using JiffyDOS. As far as switching to "1571 mode" goes, I assume you're using a C64 and trying to put the 1571 in double-sided mode. Don't try to use the JiffyDOS extensions to write the memory value. That doesn't always work in the expected way. Use the full C64 DOS command, like:
OPEN 15,8,15,"U0>M1":CLOSE 15

- Error 20 is block header not found. That means it (allegedly) wrote the track and then failed verification. I'd try making sure the head is clean. I mean get down with a magnifier and really look at it. I received a 1571 that did something similar even after I cleaned the heads blindly. After I got down and looked, I found a large deposit that hadn't dissolved. Some more cleaning to remove that and all was well.
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Re: 1571 cannot switch to double-sided mode

Post by rmzalbar »

Also, since its a 1571, look to see that top head is level and not tilted when a disk is inserted and latch is closed. The head load safety props the top head up only on one side, and so the metal strip can take a warp so that it isn't straight anymore. This might happen over years of storage with no disk in the drive, or during shipping when it takes a beating with no disk or shipping card inserted. If the top head is twisted, it can end up putting uneven pressure on the disk, and it won't fully wrap over the lower head properly for a reliable read/write. It's possible to gently tweak straight again it if it is warped, but be careful with it as you can tear or break the metal strip easily.
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banman
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Re: 1571 cannot switch to double-sided mode

Post by banman »

Hi eslapion and rmzalbar,



I am curious what is the best method and fluids to clean disk drive heads?
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Re: 1571 cannot switch to double-sided mode

Post by rmzalbar »

banman wrote: Thu Dec 16, 2021 2:34 am I am curious what is the best method and fluids to clean disk drive heads?
Isopropanol. "Head cleaning fluid" included with cleaning disks has also been just isopropanol in my experience. If it's not electronics grade, you should wipe it dry so it doesn't leave deposits behind. I prefer to use "chamois swabs" for cleaning which are a plastic stick with a small wrap of chamois leather over the end, but cotton swabs are fine.

Some notes:

- Be gentle with the heads on double-sided drives as they are often mounted on fragile strips of metal that can become warped and cause alignment or load pressure problems.

- Don't lift the top head/pressure arm all the way up, you could you could stretch the spring and affect the head pressure. Just try to open it the minimum you need to clean it well.

- Don't soak the pressure pad on single-sided drives with isopropanol, it will dissolve the glue holding it in and make a mess of it. Actually if you are using a cleaning disk on a single-sided drive, cover the top opening of the disk by taping something over it so it doesn't "clean" the top pad. You may stroke the pad with a sharp edge (perpendicular to it, not a cutting angle) to sort of fluff it up and break up any hard spots.

- Don't run a normal disk again until the heads are dry. While the heads like 99% isopropanol, disk media surfaces may not. Actually if you do need to clean a disk media surface use 70%, or preferably electronics grade watered down with distilled water, so you won't leave deposits.

- Once or twice I've had visible dark deposits on a 1541 head that just wouldn't seem to come off. This was because there were fine scratches in the head and the deposits were stuck in them. A polish with a cotton swab using Meguiar's Plast-X cleaned them out and smoothed the fine scratches that allowed them to accumulate in the first place.

Deposits are ferromagnetic of course, from disk surfaces, which is why they cause trouble. They attenuate the signal, both by the magnetic properties and by increasing the media-to-head clearance. They are also abrasive (metal oxides) and cause the drive to scratch up your other disks. We need to clean more often because media is getting older.
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banman
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Re: 1571 cannot switch to double-sided mode

Post by banman »

Hi rmzalbar,

That's great information, thanks very much! :D
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