Need help with a few mesurements on the Disk ][ Drive

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Joined: Sep 21 2008
Posts: 61

I have a Disk II drive that has both R28 and R33 pots on the Disk II Analog Card. I need some one with the same, that has a Digital Multimeter and is willing to help me out with a few measurements. You must have this analog card and it must be in a full functional, working state when you measure it. Please when you measure with your [digital] meter on the ohms setting, please measure the the following points as seen in the picture and request in this post. I would also request the most accurate measurements you can give me. I know each drive is a little different but I have no other options as it stands right now. I don't have another known good drive that 'I can just connect' to the controller card with a copy of the calibration floppy and an oscilloscope. I need the resistance values from R33 (measured from points DRTP#1 and DRTP#2 as seen in the picture) and R28 (measured from points DRTP#3 TO DRTP#4). Thanks to anyone that helps out.

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Joined: Jun 5 2008
Posts: 380
I have a similar revision ana

I have a similar revision analog board that still has the paint holding the resistors at their factory settings. R33 measures 4.52K ohms. R28 measures 4.64K ohms. Given unknown variances in capacitors, which form a critical component of these circuits, I think it would be lucky if these settings were optimal for your drive. Note that I don't see tolerance codes on the caps associated with these circuits on my drive. You would be better off putting the pots back to factory settings, which might be possible, if the paint used to freeze the pots in position at the factory is still present.

However if you have access to an oscilloscope, you don't need another good drive to adjust these pots properly. The Disk ][ technical procedures manual contains the information needed to do this. If you can't find a copy, I can send you a soft copy, off list.

Regards,
Mike Willegal

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Joined: Sep 21 2008
Posts: 61
That's the thing right now I

That's the thing right now I don't have another drive that I can just connect directly to the card without an adapter, I don't have the software, and I don't have an oscilloscope (I keep losing the bid on ebay (too much) and I don't have easy access to one (other then lugging my entire Apple II and Drive down to my old school and paying my electrical teacher a visit (and being it's winter and I don't have a car (it's really a pain, else I would of done it already)))). I've read how to do it but with a lack of these things right now, the best I can hope for is that this will work. The paint only really adheres really well to the top of the pot (where the remainder of the paint is) but the rest is since missing, knocked of probably when I first removed the board to clean the mechanical part of the drive. I could get more people to measure more of these boards and I can find a happy average that may work (it'll probably be a range of 10%-15% I guess, though). I do need to replace my electrolytic caps so I hope I get some that are pretty close to the values with strict tolerances (this may or may not help the settings). These capacitors (electrolytic) have the biggest tolerance range out of all the cap on this board, that I know. I think I also have a few more parts to replace (can't seam to get readings on a few diodes) and I really hope my LM3146/CA3146 IC is okay (they're pretty rare these days). Does anyone know of a transistor that has all the same specs as the ones on the 3146? (Just in case I have to make my own). Once I've done these replacements and changed my settings I'll give you a progress report. Thanks.

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Joined: Sep 21 2008
Posts: 61
I thought you did need anothe

I thought you did need another drive for this one. What page is that one on (clearly I'm looking at another method).

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Joined: Sep 21 2008
Posts: 61
Do you need the Apple II to c

Do you need the Apple II to control it for this test? Or can I feed it 12V, -12V, and 5V to get it to work? If I can make a portable controller I can easy take It into school without the computer and set up the drive.

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Joined: Jun 5 2008
Posts: 380
Well you do need to be able t

Well you do need to be able to set up a Disk ][ so that it is reading from a properly formatted disk while you are checking the signals with the 'scope. Creating a separate controller that would do this would be a significant engineering effort.

Regards,
Mike Willegal

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Joined: Sep 21 2008
Posts: 61
Thank you very much for these

Thank you very much for these setting! I replaced the capacitors, got the speed back up to 300RPM and I set the pots to your values and it works!!!!!!!!!! So happy!!!! Thank you!