ingoldsb@ctycal.UUCP (Terry Ingoldsby) (02/02/90)
I have an interesting problem that someone out there who has an IC master might be able to help me with. I have an ancient (venerable) computer that uses a 96 tpi double sided double density floppy disk drive. Due to the fact that one of my (late) nephews knocked it on the floor and cracked the head, it doesn't work anymore. The drive was the old fashioned low density type drive, not withstanding it having 80 tracks. ie. it ran at 300 RPM and laid down twice as many tracks as a conventional PC floppy drive. Thinking that since a PC high density drive also has 80 tracks per inch, and that the only difference was the rotational speed, AND that the data format is generated by the disk controller, I bought a high density 1.2 MByte disk drive. Every drive I had ever seen before had a pot on it to adjust the rotational speed. Not this one. The motor, a direct drive affair, is driven by a chip marked: B 839008 M51785SP I believe it has 32 pins. Monitoring the pins with a scope indicated an oscillator that seems to be controlled by a small, green, square edged device on the printed circuit board, about .7 cm wide, .3 cm thick and .5 cm high. The device appears to be a ceramic capacitor EXCEPT for the fact that all other caps on the board are silk-screened as C1, C4, etc. and this one is called Y01. Removing the unidentified component caused the motor to slow to a crawl, and the oscillator to stop. Putting any cap I had in my junk box in place of Y01 caused the motor to whirl like a dirvish. Either this is supposed to take a very small cap (a few pF) or else it is something other than capacitor. The resistance of the original green device appears to be infinite. The device is much too small to be a crystal (I've forgotten the oscillator frequency, but I think it was about 800 KHz). Any ideas? -- Terry Ingoldsby ctycal!ingoldsb@calgary.UUCP Land Information Systems or The City of Calgary ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsb
whit@milton.acs.washington.edu (John Whitmore) (02/03/90)
(Terry Ingoldsby writes: >indicated an oscillator that seems to be controlled by a >small, green, square edged device on the printed circuit >board, about .7 cm wide, .3 cm thick and .5 cm high. The >device appears to be a ceramic capacitor EXCEPT for the >fact that all other caps on the board are silk-screened as >C1, C4, etc. and this one is called Y01. Well, you have definitely found the frequency-setting component. It is a crystal resonator made of a polycrystalline material (ceramic), and "poled" into the correct behavior by electrical biasing while it was being boiled in oil... Such ceramic resonators, and the similar ceramic filters, are cheaper than quartz crystals, and more than accurate enough for most applications. The "Y01" is a crystal designation, and I guess the ceramic components are close enough to qualify. Usually a replacement for such a component would be a "pi" network; input node to capacitor to ground and to an inductor, other end of inductor to capacitor to ground, and to the output. Replacing the inductor with a quartz crystal, this becomes a parallel resonant crystal circuit. If you want to change the value, find capacitors and an inductor such that 1/SQRT(L * C) = 2*pi*<frequency> where 1/C= 1/C1 + 1/C2 for the two capacitors Depending on the nature of the resonator, it may have external capacitors already connected in the appropriate spot. Good luck. I am known for my brilliance, John Whitmore by those who do not know me well.
blarson@dianne.usc.edu (bob larson) (02/03/90)
In article <324@ctycal.UUCP> ingoldsb@ctycal.UUCP (Terry Ingoldsby) writes: >I have an ancient >(venerable) computer that uses a 96 tpi double sided double >density floppy disk drive. >Thinking that since a PC high density drive also has 80 tracks >per inch, 80 tracks at 96tpi you mean >and that the only difference was the rotational >speed, Nope. They use different magnetic media (not interchageable), different clock speed, and probably different read/write heads. > AND that the data format is generated by the disk >controller, partially true > I bought a high density 1.2 MByte disk drive. Mistake. As far as I can tell, even the ones that claim to be able to handle both formats don't. Do yourself a big favor and buy a good drive, like a TEAC 55f. (I've never hand any problems with them, like I had with several other brands.) Don't get stuck with a 55g or any other HD drive. The 720k 3.5" drive I have works with no problem as a second drive. -- Bob Larson blarson@dianne.usc.edu usc!dianne!blarson --** To join Prime computer mailing list send mail to **--- info-prime-request@ais1.usc.edu or usc!ais1!info-prime-request