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Shugart 800 has read errors past track 8?

A

atod

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Oct 14, 2010
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Folks,

I finally configured my ImageDisk machine and hooked it up to my Shugart 800 8" drives. So far, one drive out of two works. I can read in 8 tracks (that have valid data), then the drive starts to encounter read errors on all higher tracks. I used a different formatted disk and have the same results. This leads me to believe it's possibly some issue with the position of the head after it's stepped? Ideas / suggestions?

I tried using the "Alignment" feature of ImageDisk and everything is ok up to track 8, but then when pressing the (R)ead key, tracks 8 and higher fail the read operation.

The other drive doesn't appear to read at all. For some reason I can format it and watch the stepper motor step the head in track by track. When I try to read from it or use the alignment tool, ImageDisk returns back "N". I looked and the drive is retuning Fault, Track 00 (when it's clearly not positioned over track 00) and WP. I checked for the Index pulse with a scope and it's there. Any ideas on this?

Any help is appreciated.

Thanks,
Nick
 
I have a setup similar to yours, and so I have some suggestions for things to check.

First, I have noticed that the head position lead screw can have dust and junk get stuck in the grease and get pushed out to a position on the screw that causes the carriage to bind. Have you run the head all the way from track 0 to 77 and back by hand (power off, of course)?

Assuming the head is moving freely, there are other things to check. The head load solenoid arm has a piece of foam on it that is usually always rotted by now. This foam pushes against the diskette jacket. The same metal arm also lowers the plastic arm that has a felt button that presses against the non-data side of the media. Quite often the felt button is shot. Be sure to check the foam and felt.

When imagedisk is running in the alignment mode, there is a tone played that corresponds to the quality of the alignment. On the eight good tracks, is the tone always the same high pitch? What happens on the ninth track?

Have you tried stepping the head out to a track beyond eight, then unplugging the stepper motor, then advancing the head by hand to try to find the track?

Lou
 
Lou - N2MIY said:
I have a setup similar to yours, and so I have some suggestions for things to check.

First, I have noticed that the head position lead screw can have dust and junk get stuck in the grease and get pushed out to a position on the screw that causes the carriage to bind. Have you run the head all the way from track 0 to 77 and back by hand (power off, of course)?
Click to expand...
On one drive the head moves ok across the tracks. The other drive it does, but only if I'm in format mode in ImageDisk.

Lou - N2MIY said:
Assuming the head is moving freely, there are other things to check. The head load solenoid arm has a piece of foam on it that is usually always rotted by now. This foam pushes against the diskette jacket. The same metal arm also lowers the plastic arm that has a felt button that presses against the non-data side of the media. Quite often the felt button is shot. Be sure to check the foam and felt.
Click to expand...
I did check that foam and it looked ok. At least OK enough that it was pressing firmly against the disk jacket. I'll try replacing it just to be sure. Does this impact how flat the disk lays against the head?

Lou - N2MIY said:
When imagedisk is running in the alignment mode, there is a tone played that corresponds to the quality of the alignment. On the eight good tracks, is the tone always the same high pitch? What happens on the ninth track?
Click to expand...
The tone is the same pitch across the tracks even beyond the 8th track (for the drive the is somewhat working). The problem is if I press the (R) ead key, it results in failure after 8th track. Not sure what that means.

Lou - N2MIY said:
Have you tried stepping the head out to a track beyond eight, then unplugging the stepper motor, then advancing the head by hand to try to find the track?
Click to expand...

Not yet. I'll try this. Would that rule out a faulty stepper? I figured as long as the head was stepping in, the motor was ok.

Thanks
 
Sadly, this is also symptomatic of worn heads. A scope would be useful in determining this.

Absent that, try telling ImageDisk you have a 1.2MB 5¼" drive and test the drive at 300Kbps (double-density). If it fares better, that's another vote for the heads.
 
I hooked up an old scope and ran through the service manual tests. I looked at the read data voltage levels and for one drive (that doesn't read ANY track) they are too low. The other drive that can read only tracks 0 - 8, the voltage levels are just barely below the minimum (110 millivolts).

I think I need at least one new head. Does anyone know where these can be found? I'm guessing nowhere as they would be around 30 years old.

Thanks

Here are some pics showing the felt and foam is ok:
img1072l.jpg

img1073au.jpg

img1075yv.jpg

img1076q.jpg

img1078h.jpg
 
By the way, there are some Qume Qumetrack 842's listed on Ebay. If I can't get replacement heads for these Shugarts, I may purchase the Qumes. Does anyone have experience with the 842s? From what I read, they are DSDD which is pretty cool.

Nick
 
Whats interesting is as I increase the track number (step head inward) the signal amplitude goes down. It appears if the read signal coming from TP1 & TP2 is less than ~160 mV, read errors occur. I tried formatting my own floppy in this drive 500k MFM DD. I can read tracks 0 - 60 back, but as I approach track 70+, read sensor voltage < 160 mV and read errors occur. I notice with another floppy someone made for me, the situation is similar, but I can only go to about track 8 or 10. The signal is much weaker coming from that floppy. Does this mean the sensor is just weak and needs replacement?

The other drive (that can't read at all) has barely any voltage from the read sensor. I'm certain that head is broken.

Thanks
 
atod said:
...The other drive (that can't read at all) has barely any voltage from the read sensor. I'm certain that head is broken.
Thanks
Click to expand...
Should be easy enough to compare resistances with the 'good' one and inspect visually.

Are you absolutely sure this isn't a mechanical issue, not enough clearance on the head lift mechanism or something warped so that the pressure on the head decreases as you step in?

A curiosity question: these drives look like they have 110VAC drive motors, so do they still need 24VDC like the newer ones? What about the Qumes?
 
Come to think of it, check the condition of the little felt pad on the side opposite the RW head. Sometimes the glue holding these dries out and the felt falls off. The head then can't make good contact.
 
MikeS said:
Should be easy enough to compare resistances with the 'good' one and inspect visually.

Are you absolutely sure this isn't a mechanical issue, not enough clearance on the head lift mechanism or something warped so that the pressure on the head decreases as you step in?
Click to expand...

I'm going to double check this and the felt issue Chuck brings up now.

MikeS said:
A curiosity question: these drives look like they have 110VAC drive motors, so do they still need 24VDC like the newer ones? What about the Qumes?
Click to expand...

Yes that is correct. They also have 24VDC supplied to them.

I suspect the Qumes run only off VDC, maybe 24V, from looking at pictures of them.
 
Chuck(G) said:
Did you say 500K (HD) or 300K (DD)?
Click to expand...

I just tried formatting the disk 300K MFM DD and reading back seems more reliable.

Do you know why this is?

DD utility readme indicates that 8" is 360 RPM and 500K rate. By the way, I'm using an Adaptec SCSI floppy controller which DD lists as completely compatible.

Thanks
 
I just tried formatting a disk 300K rate FM 128 byte 26 sectors. Everything reads back good without read errors. Would that be because the DD encoding works better with bad head sensors?
 
I think the felt is ok. Here is a pic. It does press the disk up against the head. Is there some other felt I should be checking?

Thanks

photohr.jpg
 
atod said:
I just tried formatting a disk 300K rate FM 128 byte 26 sectors. Everything reads back good without read errors. Would that be because the DD encoding works better with bad head sensors?
Click to expand...

Yes, the distance between flux transitions at 300K is about 150% of that of data recorded at 500K. So it does look like worn heads. A shame, really.
 
Chuck(G) said:
Yes, the distance between flux transitions at 300K is about 150% of that of data recorded at 500K. So it does look like worn heads. A shame, really.
Click to expand...
Now that's a trick I wouldn't have thought of; I couldn't see how anything not mechanical could change as you move in, and of course when you step in they get even closer...
 
MikeS said:
Now that's a trick I wouldn't have thought of; I couldn't see how anything not mechanical could change as you move in, and of course when you step in they get even closer...
Click to expand...

Someone else indicated that the signal would be less as I stepped the head in.

For $125 ea I'm thinking of picking up a couple QumeTrack 842s... I cringe at the thought of spending more $$$ on these computers, but I have no idea where to get Shugart heads.

Chuck - do you know if the QT 842s will fit in the same cabinet as the Shugart 801s? I'm not sure if they have the same form factor.

Thanks
 
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