• Please review our updated Terms and Rules here

8" Drive Woes

RichCini

RichCini

Veteran Member
Joined
Aug 7, 2005
Messages
547
Location
Long Island, NY
All --

It's been a while since I've undertaken a new S100 project on my IMSAI but a few weeks ago I bought a dual-drive 8" disk system for my IMSAI. I actually have a working system now that's based on 5.25" HD drives emulating an 8" DSSD and connected to a CompuPro Disk 1 controller (this was the subject of my MARCH workshop presentation in 2010). The drives are Shugart 801's jumpered as 800 and per the CompuPro manual. Host to drive communications works (RECAL command is successful) and at one point, I was able to boot CP/M and even format some disks. Then, I started getting Bdos errors and now disks won't format. I tried swapping drives and I get the same errors with the second drive.

So, I switched back to the 5.25" drives and they work fine, so it's not the controller. I cleaned the heads with an 8" cleaning diskette but that made no difference. I also checked the head pressure pad and it seems fine. For diskettes I'm using new IBM Type 1 disks, but I have a few 3M ones as well and they all exhibit this problem now. I have not checked the drive rotational speed...probably need to do that.

I'm kind of stuck at this point so I thought I'd ask the group for advise. I'd really like to get this working since the drive system would better fit period-wise with my IMSAI, but I'm getting kind of discouraged at this point. Hopefully it's something easy to fix. Any advice would be appreciated.

Thanks!
 
Rich, just a few quick suggestions:-
Check motor screws are not loose.
Make sure head worm screw is clean.
Double check jumpers/connections.
Check all voltages, 5, 12 (-5 or 12 I seem to remember on those drives) and if motors use 120AC check that.

If you can read on commercially formatted software distribution disk but not you’re reformatted disk then head alignment problem.
You really need a scope to go further checking all signals. Unexpectedly it’s often a simple connection rather than say a head amplifier etc.
I have a Diagnostic program here:-
http://s100computers.com/My System Pages/ZFDC Board/ZFDC.htm (bottom of page)
Which you probably could hammer into shape to test your system.
Start with head/track stepping. Must work reliably over say 5 minutes.
Then try reading track ID, sequentially then random. Unless that works don’t go further.
Then sequential sector reads, and then random sector reads.
If possible use a write protected known good disk

Good Luck
John
 
RichCini said:
at one point, I was able to boot CP/M and even format some disks. Then, I started getting Bdos errors and now disks won't format. I tried swapping drives and I get the same errors with the second drive.
Click to expand...
With these symptoms, I'd be first checking anything common to both drives - do they share a power supply? Cables? It's less likely that alignment would drift simultaneously on two drive units, unless you had loosened both adjustment controls, eg. while cleaning or lubricating the units, or from prolonged vibration in transit.

ImageDisk also includes a handy test program (runs on DOS) for most of the tests John M suggested.

Rick
 
John/Rick --

Thanks for the guidance. Most of the basic stuff checked out when I tested it a few weeks ago after the drive system arrived but I will have another look at the power supplies in the drive box. For clarity, it's a Lobo Systems external drive but really it's two Shugart 801 drives and a power supply...very simple. Spindle motor is 120VAC.

Also, it did work properly for a while, even though it was for only a few days. So, the jumpering is fine. I was careful to not move any adjustment screws on anything -- I just lifted the pressure pad arm, which is spring-loaded, to inspect it. I will have to look at them again in case I did something wrong there.

On the surface, stepping appears to work because the RECAL command moves the head to track 20h and back and I get a "success" response from the controller. Also, when it did format, I watched it with the cover open and the head stepped just fine.

I downloaded the ZFDC test program and so long as it works with the 8272 on the Disk 1, maybe I can hack something together to use as a test program.

Thanks guys!
Rich
 
See if you can see the surface of the actual r/w head(s). What you describe is very like build-up of oxide on the head. I had that problem once. Most of the head cleaners don't scarpe the stuff off. You may need a mirror or remove some screws. I actually used a blade to scrape the surface clean. It is very hard material.
 
I have some time this afternoon. Maybe what I'll do is pull the drives again and give the heads another once-over with a cotton swab and alcohol. I just have to make sure it's not "rubbing alcohol" and that it's kind of pure. I don't think I have regular denatured alcohol "in stock".

Thanks again!

Rich
 
Good idea. You really have to look carefully the build-up is actually a thin black line like streak across the middle of the glass like head.
 
monahan_z said:
Good idea. You really have to look carefully the build-up is actually a thin black line like streak across the middle of the glass like head.
Click to expand...

That is the pole piece of the read write head. On one end, you'll see the tunnel-erase lines on either side of it.

Build up are smudges all over the surface. The read part of the head is the line without the tunnel-erase poles on either side. That needs to be absolutely clean for best results.
 
Do not use a razor blade to try to scrape deposits from the heads. Q-tips and alcohol is all that is necessary.

The drives probably need alignment to bring them back to operating condition.

Cleaning the stepper worm screw may help head alignment, if lubricant placed there has deteriorated. Don't add more lubricant, with the power off, use something like "Goof Off" on a cloth rag to remove the old lubricant, and leave the worm screw dry.

Personally, I would guess that the problem is index pulse length (too short), OR index pulse timing. You will need an alignment disk, and a drive stepping program, and scope or standalone drive alignment tester or sort out a index problem. This is a common problem on old Shugart SA800/801 drives, and sometimes requires replacement of the index pulse sensor to fix.

Excessive head settling time can also cause a problem on old floppy drives.

If you can't figure out the problem yourself, I charge $100 a drive (plus shipping) for an alignment including minor parts replacement/repair (does not include major parts like motors, heads, and logic boards) on Shugart SA-800/801.
 
Some deposits, especially after they've aged are almost immune to alcohol. For those I use a bit of carefully applied acetone or perc. The old-school head cleaner solvents used Freon TF, but that's been illegal for quite some time now. But if you have some, feel free to use it.
 
If you are careful a scraper/razor works fine. The oxide material snaps off the glass like head surface like paint on glass. Don't be scared, the material is far harder than you might think. If you don’t want to do this, use "Goof Off" and a Q tip. I have rescued about 6 drives like this over the years. In spite of some being “hammered/banged about”, I actually never have needed a head alignment. I have an 8” alignment disk/cats eyes etc. setup etc., just never needed it. There is always a first time, but typical alignment problems are being able to read your own formatted disk but not those of others or excessive read errors at inner tracks. Since you have problems always, I suspect oxide buildup on the head.
Go ahead with the above it’s not difficult.
John
 
Have you used ImageDisk to test the drive connected to a DOS box? I did that and also hooked up my Shugart drives to a scope. I was able to move track to track with ImageDisk and use a scope for watching to voltage on the read head. I compared the voltage waveform to the service manual and the voltage was too low. The heads were bad.
 
atod said:
Have you used ImageDisk to test the drive connected to a DOS box? I did that and also hooked up my Shugart drives to a scope. I was able to move track to track with ImageDisk and use a scope for watching to voltage on the read head. I compared the voltage waveform to the service manual and the voltage was too low. The heads were bad.
Click to expand...

Before you try measuring the head output voltage, you must clean the heads, and determine that the head load pad (on single-sided drives), and head load pressure is adequate. Other reasons for low head read output include: a defective spider clamp, which can prevent the drive from clamping onto the disk and keep the disk from laying flat under the head assembly, and a defective head load assembly. You should know that in many cases on Shugart 8" drives, if the head read output is a little low, the drive might still work just fine, especially if the drive has one of the newer LSI logic boards (as opposed to the earlier analog logic boards). And, a bad write chip on the logic board could be the cause of a low recording on the floppy disk, which could result in low head output. A bad head is not the only reason for low head read output.

I would not trash a drive (or replace the head assembly) of a drive that exhibits low head read output, until after other reasons for low head read output voltage are examined.
 
Thanks, everyone. There's a lot of good advice here. The version I have is one of the newer LSI boards and the head movement is fine (stepping, REACL) so I'm going to start simple. I just have to clear a spot in the shop to spread out so I can work on it better. I'll report back when I've had a chance to work on it a bit.
 
You must log in or register to reply here.
Back
Top