ws1i+@andrew.cmu.edu (William Manchester Shubert) (11/16/87)
Somebody I know wanted to know how you alter the speed on your floppy drive (to set it to the proper 300 rpm, or whatever it should be.) They've gotten theirs open, found what they call a "meter" of sorts, but now cannot figure out how to uncover the actual speed that their drive is running at. Can anybody help?
fyl@ssc.UUCP (Phil Hughes) (11/21/87)
In article <oVbq70y00V4EzAk0HD@andrew.cmu.edu>, ws1i+@andrew.cmu.edu (William Manchester Shubert) writes: > > Somebody I know wanted to know how you alter the speed on your floppy > drive (to set it to the proper 300 rpm, or whatever it should be.) They've > gotten theirs open, found what they call a "meter" of sorts, but now cannot > figure out how to uncover the actual speed that their drive is running at. > Can anybody help? Most floppy drives have a strobe disk on the motor drive. To check the speed you need to strobe it with 60HZ. A neon bulb will do the trick. Either get an NE-2 and resistor and plug it in or get one of those $.49 elcetrical testers which is a neon bulb in a plasicc case, plug it in tio the ac line and hold it next to the strobe disk. -- Phil Hughes, SSC, Inc. P.O. Box 55549, Seattle, WA 98155 (206)FOR-UNIX or 527-3385 ...!uw-beaver!tikal!ssc!fyl
schuster@dasys1.UUCP (Michael Schuster) (11/24/87)
In article <797@ssc.UUCP> fyl@ssc.UUCP (Phil Hughes) writes: >In article <oVbq70y00V4EzAk0HD@andrew.cmu.edu>, ws1i+@andrew.cmu.edu (William Manchester Shubert) writes: >> >> Somebody I know wanted to know how you alter the speed on your floppy >> drive (to set it to the proper 300 rpm > >Most floppy drives have a strobe disk on the motor drive. To check the >speed you need to strobe it with 60HZ. A neon bulb will do the trick. I heartily agree. Recently I had some problems with extended formats and interchange of disks with friends, so I decided to look at this in detail. Ever check your drive speed using the only (to my knowledge) public domain speed checker? It's called DSPEED.TOS and was written by Mike Curry a long time ago. It seemed strange that most (hmmm, come to think of it - ALL) of the disk drives I tried it on ran a little fast - from 302-304 rpm. Well recently a friend, who has been using IBM-vintage 3.5" drives on his ST, told me an interesting story. He said that he tweaked his drive speed to 300.030 using DSPEED.TOS, and then connected the drive mechanism to his IBM. Using an MS-DOS disk speed program he got 297 rpm!!!! The solution, as suggested, is to use a strobe disk. Trouble is, not many ST drives have one. I stole one off an old dead Tandon mechanism and put it on my SF314's flywheel. Lo and behold, DSPEED.TOS reads 303.54 when the strobe is exactly stationary. Conclusions: 1. If you can get one, adjust your disk drives with a strobe disk. 2. Beware of DSPEED.TOS; 303-304 rpm by it's reckoning may very well be right on the mark! ----- -- l\ /l' _ Mike Schuster {sun!hoptoad,cmcl2!phri}!dasys1!schuster l \/ lll/(_ Big Electric Cat schuster@dasys1.UUCP l lll\(_ New York, NY USA DELPHI,GEnie:MSCHUSTER CIS:70346,1745
870646c@aucs.UUCP (11/24/87)
Please correct me if I am wrong, but isn't the drive speed on the ST drives controlled by the strobe only, I had a look at one at the shop and it looked as if there were no adjustments??? later Barry
rwa@auvax.UUCP (Ross Alexander) (11/24/87)
Muke Schuster and others have written about setting drive speeds, et c., and the fact that strobe wheels are a a good deal more accurate than DSPEED.TOS or whatever. Fine. But there has been an unspoken assumption all along, and that is: You want your drive to be going _exactly_ 300 RPM. I question this. Yes, that's the specification alright, but there is a good reason to run your drives a little bit SLOWER (say, 297 RPM or so). The reason is thusly: if you are using one of those clever formatters, such as DCFORMAT or any of its ilk, that can put 10 sectors on a track, the last gap (Gap #4, made out of 0x4e's) gets a little bit shorter than normal, which is 1401 bytes; it gets trimmed down to 780-odd bytes. It's not a bad idea, however, to run slightly larger than normal Gap 3's (normally 40 bytes, I like to double this), and then Gap 4 really gets crowded. But if you run the drive a little slow, the effect is that to the 1770, all the tracks look a little longer than normal, and you get your Gap 4 size back to something reasonable. You can check this by looking at the data coming off the read line with an oscilliscope (take the scope sync input from the index pulse line) and noting how close the end of the last sector comes to the end of the track. I have done this routinely for years and find it doesn't generate any trouble if you are only 1 or 2% slow; the PLL in the data separator can handle this kind of an error with it's eyes closed, and the added security of the longer gaps helps to overcome all kinds of write-skew and drive wow-and-flutter problems. Ross Alexander @ Athabasca University, alberta!auvax!rwa