Floppy disk head alignment

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VicViper
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Floppy disk head alignment

Post by VicViper »

Hello,

This is my first post on the forum. I am searching for a program that will help me align the head on the PCjr floppy drive. I have done this on a Commodore 64 1541 before using a cartridge utility on that system.

I have a JR-IDE so I can load software on the CF card without using the floppy drive, I am just having difficulty finding an alignment utility that works with the PCjr.


Thank you.
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chuckphd53
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Re: Floppy disk head alignment

Post by chuckphd53 »

Vic...

Suggestion, On Youtube, Adrians Basement:
He has a couple videos on how to align the heads on drives.
Maybe take a look..

Chuck
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Re: Floppy disk head alignment

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I have seen those videos.

I already know how to align the heads on the drive, it is mechanically very similar to the Commodore 1541. I just need a utility that does read tests as I am adjusting the drive that works on the PCjr.

I have tried imagedisk as it has an alignment test, but it does not like the PCjr. Doesn't even spin the disk. Just says "No FDC Interrupt."

I am currently testing on my PCjr that has a perfectly functioning drive. Once I get a utility that works on that I can use it on another PCjr that has a drive that kind of works and has trouble finding tracks and than errors out.

The Commodore 64 utility would tell me what track was being read, and how aligned to that track it is 0-100%, and it would also test the half-tracks, on that you want it as close to 0 as possible, but usually got 30-40%. The half track aligning on the 1541 was some what black magic, but needed to be quite close so copy protected programs would work.
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Re: Floppy disk head alignment

Post by chuckphd53 »

Got it, I will look around, but I have not heard of a program specifically for the Jr, so maybe an alternate DOS 4.0 or ealier style program may be out there..
“I never commit to memory anything that can easily be looked up in a book.” (AE)
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Re: Floppy disk head alignment

Post by chuckphd53 »

Found this ..
Looks like Version3 may have floppy alignment stuff.


https://winworldpc.com/product/checkit/30
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Re: Floppy disk head alignment

Post by RLumpy »

The last version of Checkit I tried on the PCjr loaded fine but the keyboard did not function. I can't recall the version I tried but I think it was 3.0.
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Re: Floppy disk head alignment

Post by RLumpy »

Update: I downloaded and installed this version of Checkit and it works fine on my PCjr.
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Re: Floppy disk head alignment

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I tried Checkit 3.0 on my PCjr and its disk alignment program doesn't even spin the disk. This is on the known good drive that I can load games on and play just fine. Checkit 2.1 was able to spin the disk and do random read and random write tests, but it didn't give any useful alignment information. Just said nothing and moved on to the next random track.

So I dug out another computer that is much more modern, but still has an on motherboard floppy disk controller that knows how to talk to 360k and 1.2 MB drives.

On its 1.2 MB drive using imagedisk's alignment tool it was able to test alignment to a standard formatted 360k disk.

So I set its motherboard to 360k drive and tested the bad drive. When changing between tracks it always skipped a track. (This is done manually with - / + keys.) So it went from track 0 to 2 to 4 etc. And than after a while it wouldn't track right at all correctly and started having issues moving its head. So I connected the known good PCjr floppy drive and tested it and it advanced one track at a time like it should all the way to 39 (this program starts count at 0) Both PCjr drives are exactly the same model and have the jumpers configured exactly the same.

So something else is wrong with this drive.
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Re: Floppy disk head alignment

Post by chuckphd53 »

Is this a PCjr original Drive ?

Not an easy path, but you may need to write your own program, using the FD INT routines to control the drive..

this would not be hard program to write, and there are lot's of folks with experience in this, may need to find time.
but it can be done...

This is a good topic so I would like to know more as progress is made.....
I will keep looking for some path to take..

Can you do a quick write up, a few steps on what exactly you would want a program to do if someone writes one....
This would be a very handy utility to have for the Jr..... I can't imagine there is not a utility already out there...
but finding it may be the issue.. and have it work on the Jr...

Chuck
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Re: Floppy disk head alignment

Post by VicViper »

OK, I might have been a bit too wordy on my last update.

Let me recap my last post.

Both the bad drive and the good drive are IBM PCjr OEM devices that came in the machines.

Checkit 3 doesn't spin the drive on the disk test.
Checkit 2 only does random track tests.

So I dug out a newer machine that can still control 360k drives and tested both IBM PCjr drives with Imagedisk.

Imagedisk allows me to manually moved through tracks with - / + keys.

The BAD drive would only change tracks by 2 and kept skipping a track. 0,2,4, etc. than after a while would have trouble tracking at all.
The GOOD drive would change by 1 track as it should.

The problem with the drive doesn't seam to be an alignment problem but something else. There is a little trimmer pot next to the stepper motor connector that is giving off 'twiddle me' vibes, but it got late and I got tired, so I will come back to this and give an update.
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Re: Floppy disk head alignment

Post by chuckphd53 »

The trimpot may be a bias adj for the write head function....
Does anyone have the schematics for the disk drive ?

It sounds like there is a bad chip driving the stepper head motor....

I would find the stepper motor cable and use some cleaner and reseat it a few times... just incase there is some oxidation, resistance build up that
may be causing a noisy signal to the motor and making it double step....
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Re: Floppy disk head alignment

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OK, the pot I am talking about is down by the motor controller. It is right next to the power transistor is connected to the motor control circuits. It is the speed control pot. Adjusting it did help. The motor wasn't spinning at the correct speed.

The one you are thinking about is in the front by the disk activity light. It is also close to where the heads plug in to the board.

I adjusted the speed using the strobe speed indicator on the disk spindle. Just like adjusting a vinyl record player.

I also cleaned and lubed the guide rails with some light sewing machine oil. As well as the stepper motor and spindle motor barrings.

Than I aligned the heads and tested alignment throughout its entire 40 track range and had it jump around a bunch to make sure.

I than put it back in the PCjr and played Kings Quest for a while. Its working perfectly now.
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Re: Floppy disk head alignment

Post by chuckphd53 »

Great job, congrats!

And I have yet to complete a level of Kings Quest...:)
“I never commit to memory anything that can easily be looked up in a book.” (AE)
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