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Help repairing 810 disk drive

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Years ago I found an 810 disk drive in the trash along with an 800, a 1200XL, and a box of disks. I've restored the 1200XL and am finally getting around to the 810. This 810 has the old-style rear board, and I know that the problem must be either with the rear board or the drive mechanism itself because I'm using a known good Rev C side board with data separator. I also verified 5V and 12V on the rear board; I had to replace the 12V pass transistor because it was shorted and passing 24V!

 

So far, I've tried swapping out all the ICs on the rear board, but no luck. The drive goes through the normal power-up sequence, but when I insert a disk and turn on the computer, it alternates every few seconds between trying to zero the head (pushing against the stop since the head is already there), and beeping once with a "boot error" message on the screen.

 

Any advice on what to try next? I do have an oscilloscope if it would help to look at some signals.

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First thoughts are either RPM too far out of spec, dirty head, or pressure pad.

 

Hmm, RPM will be difficult to measure using software if it can't read anything...

 

Check the pressure pad, and if its still there and good, try adding a little more pressure with your finger and see if its able to read anything...

 

I will be adventuring into repairing some similar drives with old power/analog boards too soon, but up until now ive only had my head in drives with all the newer parts. Those old power boards will be highly suspect though from what I've read about them - RPM's can wildly change.

 

Make sure your're using a good 9V AC PSU with at least 2A, although those older power boards with power transistors instead of linear voltage regulators in the later design supposedly required less.

 

Edit: Can you confirm you're maintining a solid 12V even with the disk spinning?

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Thanks for the advice Nezgar!

 

I thought maybe RPM too, so I tried turing the pot to change the speed. I could clearly hear and see the motor speeding up and slowing down, but no change in boot activity.

 

12V seems solid, it measures 12.4 at the pass transistor when nothing is happening, and drops only slightly to 12.3 when the disk starts turning. The 24V feeding the pass transistor drops much more significantly, I measured around 18-19V when the motor was turning.

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as always clean and reseat all boards and chips, it an 810 after all...

you can set rpm using a 60hz timing light and using the pattern on the spindle, if it does not have one you can print one and affix it to do so.

double check all voltages and follow the 810 fsm available on atarimania.

 

does the mech still work with another know good 810's electronics? is it the same mech type in both?

don't forget to blow the track zero sensors etc out clean, verify they are putting out light with and ir detector card (its a card the size of a credit card with a uv only reflector) or old camera/ phone that doesn't have a u/v filter

Edited by _The Doctor__

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2 hours ago, _The Doctor__ said:

you can set rpm using a 60hz timing light and using the pattern on the spindle

That will get you close - 300RPM, which is the "standard" speed the MPI/Tandon mechs were designed for, but 810 drives need a little slower at 288RPM.

 

I guess if you can set a strobe for 57.6hz, you'd be good looking at the 60hz ring and get 288RPM. :)

 

Having another known good drive that you can swap mechs with is definitely a handy troubleshooting method...

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Yep I just wanted to get him in the ballpark since he 'adjusted' rpm without an idea what it was or will be. if he has another working drive he could load the rpm test  and set it that way...

 

is it hitting the back stop or the front stop?

does it move forward then back?

Is the stepper motor properly tightened to the frame?

does it look like it was loosened and re tightened by looking as the screw heads or possibly broken loctite seals?

if the rabbits felt pressure pad is still attached is the spring loaded plunger being pushed to the disk? I have an 810 where the spring on the plunger is missing...   is the pressure adjust spring on the highest step to assure maximum pressure until we have something working and can start backing the tension off?

 

Edited by _The Doctor__

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In the past, I have sprayed (dry, oil free) PTFE lube on the pad, then let it dry before using.

Never had a problem. Is this a good idea?

Has anyone tried this?

 

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Thanks for the additional advice Doctor! I confirmed the mechanism is fine by swapping it into a known good drive (the newer analog drive, incidentally). It does have the felt pad. So, the only possible place left for the problem to be hiding is the rear board. I’ve already reseated and then replaced all the chips. I suppose it’s possible that one or more of the rear board headers are faulty...

 

I do have a couple of newer power supply boards and an analog board; at this point it’s so far disassembled that I’m thinking about just doing the Grass Valley upgrade. Though it would be fun to have working examples of each version, if the old version is so unreliable I wonder if it’s worth it to debug the issue...

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For comparison since I happened to have all three:

 

On the left is rev 1 of the Grass Valley power supply, the middle is rev 2. On the right is rev 8 of the older rear board.

 

8D11940B-22C4-40CB-9352-560F6415B109.thumb.jpeg.478176e75b0337ff4ebda2603e9f809b.jpeg

 

I will probably install the rev 2 Grass Valley board. Apparently it last worked on Oct 6, 1982...coming up on 37 years!

 

E66AA919-EDCE-49A3-B45D-375778FC7905.thumb.jpeg.d0ab5167600a139bb87a566e301f4a77.jpeg

 

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Interesting that there are 2 visually different versions of the grass valley power board... I wonder why, and if it was a functional / reliability difference...

 

I also share your goal of having a working example of the older rear board. Hopefully I can achieve that as well from the selection of 810's I've recently acquired. But verifying the mechs and side boards are good with known good power/analog first is essential.

 

I suspect that paper of test results is the output of the 810 Diagnostic Cartridge. You could use that cartridge ROM with an 820 printer to make an authentic new QA certification report lol.

 

7 hours ago, Kyle22 said:

In the past, I have sprayed (dry, oil free) PTFE lube on the pad, then let it dry before using.

Never had a problem. Is this a good idea?

Has anyone tried this?

I guess that would have a remote chance of leaving some kind of residue on the (reverse side) disk surface, but does sound pretty unlikely if done carefully... Might help against some pressure pads I've had resonating generating a "whining" sound. I've used something abrasive like a pin or an exacto blade to 'fluff up' the pad that might have been well "flattened" down from years of pressure.

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8 hours ago, Nezgar said:

Interesting that there are 2 visually different versions of the grass valley power board... I wonder why, and if it was a functional / reliability difference...

i always suspect they revise the board layout to reduce the component count and the manufacturing costs...

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13 minutes ago, xrbrevin said:

i always suspect they revise the board layout to reduce the component count and the manufacturing costs...

that happens later, but in this case the revisions really were to fix and improve...

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Found two analog boards. One of the boards had test results printed:

 

A88212A7-0DF4-4A8E-9DB8-544B26B4EB46.thumb.jpeg.0eebd0f01ad484251aa7622fe1c4b934.jpeg

 

Last tested on April 27, 1983 and...as of a few minutes ago! Verified working on my known good 810 analog drive. The other analog board worked too. Guess these are just more reliable than the old design. Time to perform the upgrade; the only thing I haven’t tested is the power supply board. Off to find a 12V regulator...

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Got the regulators soldered in place, installed the boards and cables, turned on the drive and inserted a disk. Turned on the computer and it booted on the first try! The Doctor said it well...the Grass Valley upgrade is the debug :)

 

Now the only thing wrong is the power LED—it doesn’t light up. I followed the debug flowchart and it led me to CR107. On closer inspection, there’s a capacitor there when it’s supposed to be a 5V zener diode. Makes me wonder if there are other errors on the side board, but I guess if the drive reads disks ok it must be fine. I’ll put the correct part in and if the LED starts working, I’ll call it good.

 

Now I have two working 810s—no more swapping when I want to duplicate disks ;)

 

 

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