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Archive-name: apple2/faq/part9
Posting-Frequency: monthly
Last-modified: 2004/5/1
URL: http://home.swbell.net/rubywand/A2FAQs1START.html

The comp.sys.apple2 Usenet newsgroup Apple II FAQs originate from
the Ground Apple II archive, 1997-2004. Administrator: Steve Nelson

Csa2 FAQs-on-Ground ref: Csa2FDRIVE.txt  rev074 May 2004






Floppy Disk Drives


 001- How do I add a write-protect On-Off switch?
 002- How do I add external speed adjustment to my Disk ][ drive?
 003- How can I adjust my 5.25" drive for optimum performance?
 004- How do I clean my disk drive R/W head(s)?
 005- What is the pin-out for a duodisk drive connecting cable?
 006- What DuoDisk mods are necessary?
 007- Will a Duodisk function correctly on my ROM 3 GS?
 008- How do I fix a false Write Protect?
 009- My 3.5 Disk Drives don't work! What should I try?
 010- I added SCSI; now, my 3.5" drives often fail to work. Why?
 011- Both of my Disk ]['s come on when booting! Is there a fix?
 012- In connecting a Disk II I misaligned the connectors. A fix?
 013- A sound like a shotgun going off came from my drive. A fix?
 014- Uni-disk and Laser drives: neither works with my IIc. Why?
 015- How do I replace a 3.5" drive mechanism with one from a Mac?
 016- I have one 5.25" drive. Sys6 shows two icons!? Is there a fix?
 017- How can I tell a 13 from a 16-sector Disk ][ controller card?
 018- Can a Disk ][ Drive be used on a IIc or GS smartport?
 019- How do I install a bi-color LED R/W indicator in my Disk ][?
 020- What's the scoop on the 3.5" High Density drive?
 021- What is a "UniDisk"?
 022- What is a "RAM disk"; and, how do I create one on my IIgs?
 023- Which 3.5" drive/interface combinations work on a IIe?
 024- How can I boot from my /RAM5 RAM disk?
 025- My 5.25" drive ruins every disk I insert. How can I fix it?






From: Stephen Buggie

001- How do I add a write-protect On-Off switch to my Disk ][ drive?


Adding an Auto/Manual Write-Protect (A/MWP) Switch

     Often, as when doing copying, it is useful to be able to guarantee that a diskette is Write-Protected whether or not the side is notched. Other times, it is convenient to defeat Write Protection-- for example, when you wish to write to a diskette side which is not notched. And, naturally, you also want a setting which permits Normal, notch-controlled, Write-Protect.

     Based upon a circuit suggested by David Wilson (Australia), the A/MWP enhancement offers full user control of Write Protect. The switch's three positions are

Normal:      a diskette side must be notched to permit writing.
Protect ON:  Writing is prohibited regardless of notching.
Protect OFF: Writing is allowed regardless of notching.


A/MWP Step-by-Step

Unplug the drive from the disk controller and remove the case.

Drill a mounting hole. This can be at a convenient spot in the back or in the plastic front panel. On the front, a good spot is at the lower left, above and to the left of the "in use" LED. Another open spot is at the upper right in the space just above the diskette slot; but, we're saving this place for Part 2's enhancement. (You can't use the lower right, of course, because this would mess up the "Apple" logo!)

Cut three wires (Brown, Black, and White) long enough to run from the mounting point to the Large Connector plugged onto the back, middle of the Disk ][ circuit board.

Solder the leads to a Single-Pole Triple-Throw mini toggle Switch:  Brown to center, White to one end, Black to other end. Twist the leads or encase them in tubing.

Mount the Switch. Normally, the Switch handle will point ...

o- in the Black lead direction for "Normal" (center and White connected)
o- at Center for "Protect ON" (no connection).
o- in the White lead direction for "Protect OFF" (center and Black connected).


Mounting the switch with the Black lead on top is recommended because it is easy to remember that Up = Normal. Route the leads to the area next to the Large Connector. (Make sure no wires will get in the way of an inserted diskette.)

Locate the Brown and Black leads coming from the Notch Detect micro-switch. The leads are the Brown (bottom) and Black (top) pair near the right end of the Large Connector (as viewed from the front of the drive).

Cut the Notch Detect micro-switch leads about 1" away from the Large Connector.

Connect the Black Notch Detect, Black Large Connector, and Black Switch leads (i.e. strip ends, solder, and cover in heat-shrink tubing or tape).

Connect the Brown Notch Detect lead to the White Switch lead.

Connect the Brown Large Connector lead to the Brown Switch lead.


     Viola! Now you're ready to replace the cover, plug in the drive, and try out your A/MWP enhanced Disk ][.

----------------------------


From: Ed Eastman

     Most of the time what you want to be able to do with a Write Protect modification is turn On Write Enable when a disk is not notched. That is what this mod for does. Details relate to the 5.25" Unidisk but the method will also work with other Apple II 5.25" drives.

     The way the write protect sensor works on newer drives is that an LED on one side shines on a phototransistor (the sensor) on the other side. When there is a notch in the diskette you insert, light passes through the gap and the sensor 'closes' to complete the Write Enable circuit. 

     What we will do is give the Write Enable circuit an alternate enable option using an On/Off switch. A mini toggle switch is okay; but, I like to use a small normally-open momentary contact pushbutton switch from Radio Shack. It's compact, looks nice, and pressing the button for the few seconds usually required for a file, etc. write is no problem.

     I normally mount the switch in the upper left part of the face plate, opposite the light to balance the look. Drill a hole a little smaller than required and use scissors or a larger drill to taper the hold to just where you can screw in the switch. 

     Before soldering on leads and mounting the switch, decide where you want to make the connections. You can locate the output leads from the sensor and splice one switch lead to each; or, you can find the place on the circuit board where the sensor leads go and connect there.

     On a Unidisk you will see a large connector labeled "CN1" near the front. Pins 9 and 11 of CN1 are the write protect sensor connections. More convenient connection points are the circuit board edge side of R12 and the wire at J29.

     Solder on leads long enough to reach the connection points and screw in the switch. On a Unidisk, connect one switch lead to the R12 point near the edge and one to the wire at J29.

     Now when you need to override write protect on an unnotched disk, you simply press the button while writing. Go ahead and plug in the drive and give it a try.

____________________________



From: Stephen Buggie

002- How do I add an external speed adjustment to my Disk ][?

Reference: FAQs Resource file R006SPDKNOB.GIF


          Adding a Speed Control Knob to your Disk ][ Drive

     This article tells how to move speed adjustment from the Disk ]['s  dark interior to a handy front-panel location and how to  "tune" the drive for optimal performance.

     One drive-test software vendor states that Disk ][ is good for about 500 hours of normal use between speed adjustments-- not exactly a strong argument for placing the control on the front panel! On the other hand many of today's Disk ][ owners are interested in applications which go beyond "normal use".

     Some utilities (e.g. DiversiCopy II) report rotational speed during ongoing applications; so, relocating the speed adjuster to the front panel is especially helpful. Similarly, users who want to back up their old, copy-protected wares know that ready access to speed control is essential.

     Finally, there is no question that, whatever your applications, periodic speed trimming will be required. When it is, you'll be very glad _your_ Disk ][ has a front panel Speed Knob!



Adding Speed Knob

     To install Speed Knob you will need a good quality, linear taper 5k Ohm potentiometer, some wires, and a knob with a pointer mark or some other way to show position (e.g. a ring of numbers).  Most of the work, really, consists of opening the drive and drilling a hole. There is no need to disconnect the drive from the controller card.

1. Remove the 4 bottom bolts and slip off the case. Unscrew the 4 bottom bolts holding the drive to the case bottom, and unplug the main ribbon cable. The drive can now be moved to your work area.

2. Drill a hole properly sized and centered for mounting your 5k Ohm pot in the upper right front panel.

3. Place the drive on its face and unscrew the 2 bolts which hold the small daughter board to the drive. (Be ready to catch loose spacers, washers, etc..)

4. Turn the small board over to the bottom side. Locate and cut the traces going to the mini-pot speed adjuster as shown in pic R006SPDKNOB.GIF.

5. Cut three wires, White, Gray, Black, long enough to reach from the board to the front panel. Connect these to your 5k Ohm pot and to the small circuit board as shown in pic R006SPDKNOB.GIF. (In case you cannot view the pic, what you're doing is substituting the new pot for the mini-pot. )

6. Re-mount the daughter board. Mount the 5k Ohm pot. Install knob.

7. Bring the drive back to the computer. Slide it onto the case bottom plate, reconnect main ribbon cable, replace bottom bolts, slide on and re-fasten case top.

     You can use Copy II Plus, XPS, APEX, or one of several other utilities to set speed (see next question). A good starting adjustment will be near the center of Speed Knob's range. Once speed is adjusted, you can loosen and re-set the knob so that its position indicates a "correct" speed setting.

----------------------------


003- How can I adjust my 5.25" drive for the best performance?

     The typical 5.25" drive will run for months with no need for maintenance save an occassional dusting or session with a head-cleaner disk. When adjustment is required, it will usually be to fine-tune Speed or, less often, to set track centering.

     If a 5.25" drive has difficuly reading diskettes, including those it created, and head-cleaning does not help, then, the odds are it's time to adjust speed. If your drive is a Disk ][ and does not have the external 'Speed Knob' mod, look for a small hole on the lower right side near the back-- some owners add this hole to allow easy access to the Speed Adjustment mini-pot screw. If there is no hole, you will need to remove the case. (Remove bolts on bottom and slide out the drive through the front.)

     On the 5.25" Apple 'Platinum Drive', the Speed Adjustment is accessed through a small hole on the bottom of the drive near the front on the right side. Non-Apple 5.25" drives may place the Speed Adjustment almost anywhere. Look for a small hole through which you can see a screw head. If you don't fine one, remove the case and look for a mini-pot labeled "Speed" or something similar.

     The most popular speed adjustment software utility is, probably, dear old Copy II Plus. From the menu, just select "Verify", then "Drive Speed". Put a diskette into the drive you want to adjust and, turning the Speed Knob (or min-pot shaft) use Copy II's numeric speed display to zero-in on the 'magic' 200ms. number. (Standard Disk ][ rotation speed is 300 rpm, which comes out to be 0.2 seconds per revolution.)

     Other speed adjustment utilities show an rpm number or a hires pointer. Whatever, all speed check routines need to read AND write; so, you will usually need a "scratch diskette" which you do not mind having over-written.

     Track-center realignment is needed when a Disk ][ writes and reads its own disks fine, but does not 'communicate' with many other Apple II 5.25" drives. It generates disk errors when reading disks written by other drives and other drives have the same problem with its diskettes.

     CALL A.P.P.L.E's APTEST, now in the public domain, tests track-center alignment. With  this software, the user checks the alignment of the drive with disks regarded as well aligned --- such as Apple diskware supplied with the computer or some unprotected, original, commercial software diskette. (In a pinch, a diskette formatted by any drive that has no problem reading most other diskettes should be okay.)

     Basically, a track-centering test tries to step your head between two tracks of the 'standard' diskette and read the tracks on either side. If the number of successful reads from each track is about equal, the head is "centered" and your drive is well-aligned with the standard diskette.

     The test may indicate serious misalignment. ("Aha! That explains why my IIgs and II+ have problems reading each other's diskettes!")  Centering adjustment is done by slightly repositioning the stepper motor (mounted on the underside of the drive). This requires loosening the two bolts holding the stepper-motor, rotating it clockwise or counter-clockwise, and retightening.

     The adjustment/test process may require several repetitions. Each time, the program will report "differential fractions". The smaller these numbers, the closer you are to near perfect alignment with tracks on the diskette.


----------------------------


From: Rubywand

     Suppose you have just one drive and it is so far out of adjustment that it will not boot a speed adjustment utility diskette? In this case, you can remove the drive cover, turn over the drive, and (probably) find that the drive has a strobe pattern on the main pulley or flywheel.

     Set a fluorescent light near the drive (or do the adjustment in a room with fluorescent lighting).  Get the drive spinning via power-on booting or a PR#6 and adjust the speed for a stable pattern.

Note: If you live in a place which supplies 50Hz power and the drive is intended for use in the U.S. or other country with 60Hz power, you may have to experiment with + deviations in speed from a stable pattern.


____________________________



From: Rubywand

004- How do I clean my disk drive R/W head(s)?

     The easiest way to clean a drive's R/W head(s) is with a Cleaner Diskette. This is a diskette with a paper disk such as the 5.25" and 3.5" Cleaner Diskettes available in Radio Shack's Disk Drive Head Cleaner Kits. These kits usually include "Cleaning Fluid" (isopropyl alcohol), too.

     The 5.25" Cleaner Diskette has panels you pop out to expose the cleaning surface. Apple II 5.25" drives have a single head which contacts the disk from the bottom and a pressure pad which presses against the top side. So, pop out the panel on the bottom side of the Cleaner Diskette and leave the top panel in place. When cleaning, insert the diskette with the bottom side facing down. This lets the paper disk rub against the head and avoids wear on the pressure pad.

     The 3.5" diskette has a small plastic panel you can snap out for cleaning two-head drives. Since the standard 3.5" 800k Apple II drive has two heads, snap out the panel so that both the top and bottom heads get wiped.

     To clean your drive head(s), you sqirt a few drops of Cleaning Fluid onto the Cleaner Diskette disk, insert it into the drive, and get the disk spinning for 20 seconds. (Booting the Cleaner Diskette is one way to get it spinning. If DOS or ProDOS is installed, doing a CATALOG is another way. For example: CATALOG,S6,D2 would get your 5.25" Drive 2 spinning.)

     If you think it has been several months since the drive was last cleaned, repeat the procedure-- i.e remove the Cleaner Diskette, add more fluid, etc.. As a rule, do not let the disk spin more than 20 seconds for any cleaning cycle. This is especially a concern with 3.5" drives where the heads are mounted on springs and much more subject to snagging and being pulled out of alignment.

____________________________



From: Steve Jensen

005- I picked up an apple IIe and a duodisk drive at a thrift
     store. Could someone describe the connecting cable?

     I just checked the pinout on a Duodisk cable.  The numbers for the pins are inside the plug by the pins, but I'll draw them for you.


DB 19 looking at the end of the cable:

    1   2   3   4   5   6   7   8   9  10
    o   o   o   o   o   o   o   o   o   o
      o   o   o   o   o   o   o   o   o
     11   12  13  14  15  16  17  18  19



DB 25 looking at the end of the cable:  (x = no pin)

     1   2   3   4   5   6   7   8   9   10  11  12  13
     x   o   o   o   o   o   o   o   o   o   o   o   x
       o   o   o   o   o   o   o   o   x   o   o   x
      14  15   16  17  18  19  20  21  22  23  24  25


Cable

DB 19   DB 25

1       2
2       4
3       9  & 21
4       10 & 14
5       23
6       7
7       19
8       20
9       8
10      12
11      15
12      16
13      17
14      18
15      5
16      24
17      11
18      3
19      6

____________________________



From: Steve Jensen and Jonathan Adams

006- What DuoDisk mods are necessary?

     The following is excerpted from an info file from my old bbs ...

     There are TWO modifications that should be made to Duodisk drives:

     The First one was recommended by Apple several ago to solve occasional problems with trashing diskettes. The solution is to remove 2 capacitors.

     The Second modification is only required to solve a problem with daisy-chaining on the GS Smartport, though the modified Duodisk will still work fine on older Apple II's. It requires removing a resistor.



DUODISK MODIFICATION #1- REMOVAL OF TWO CAPACITORS

     This mod should be done on ALL Duodisks, no matter whether they're used on //e's, IIGS's, etc.  The problem was that diskettes would sometimes be damaged when doing an Open-Apple-CTL-Reset or when using disks with certain kinds of copy protection.  The mod was in an Apple dealer service bulletin several years ago for "analog board  PN 676-[]101 or 676-[]102."

     The Analog board is the one inside Drive 1 in the Duodisk.  You may have to unplug the cable near the back right of the board to see the board's model number.  Anyway, if you have the -101 or -102 board, just snip out Capacitors C29 and C30 at board locations A1 and B1, respectively.


DUODISK MODIFICATION #2- REMOVAL OF A RESISTOR

     This mod should be done for Duodisks used with a GS; otherwise, it is optional. The problem is that the Duodisk draws just a little too much current when connected to the GS Smartport. This can render other drives on the chain inoperable. Problems are MOST likely to occur when the Duodisk is daisy-chained from a Unidisk 3.5 Drive.

     Remove the top cover and turn the drive so that the identifying number will be at the bottom left of the analog board. The number might read 676-[]101, 676-[]102 or 676-[]107. (ROM 3 GS users should check Q&A 007.) 

If the I.D.# for the analog board is 676-[]101 or 676-[]102, use a pair of nippers and cut out resistor R8 (located at position A2).

If the I.D.# for the analog board is 676-[]107, use a pair of nippers and cut out resistor R39 (located at position C3).

----------------------------


From: Dave Althoff

     There are two capacitors which must be clipped from the board on the DuoDisk regardless of what machine you intend to use them on.  Failure to do this can lead to very nasty failures. For instance, some copy-protection schemes can cause the drive to start writing unexpectedly-- say, during a re-boot-- thus trashing the disk without regard to the write-protect switch.

----------------------------


From: Chet Gerhardt

     I have done the capacitor removal mod with all DuoDisks I have sold and my own DuoDisks. It is amazing that after all of this time most still have not had the mod done.


____________________________



From: Steve Buggie

007- Will a Duodisk function correctly on my ROM 3 GS?

     I have three Duodisks.  The one connected to my flagship ROM 3 IIgs has had the resistor and capacitors clipped out as recommended in a memo from Mitch Spector. It works perfectly!

---------------------------- 
  

From: Rubywand 

     A Duodisk may not be entirely functional connected to the usual ROM 3 "Disk" connector (i.e. the SmartPort).  Users report that the system may not start up unless a write-protected disk is inserted in the Duodisk. Apple, in Tech Library notes #5010 and #5434, mentions these reports and says that there is some code in the ROM 3 ROM that does not handle the interface to a Duodisk properly. Apple's workaround is to connect the Duodisk to a drive interface card instead of to the Smartport. 

____________________________



From: John L. Graham

008- How do I fix a false Write Protect?

     I recently ran into this problem with a Disk II. It insisted the disk was write protected. I checked the write protect switch, but it was okay. I pulled all the chips out of the analog board inside the drive, cleaned the contacts with a clean pencil eraser (one was _really_ dirty, almost looked burnt) and re-installed them. Voila! The problem went away.

____________________________



From: Rubywand

009- My 800K, 3.5 Disk Drive is no longer working on my IIGS.
     When a disk is inserted the drive tries to read it and then
     locks up the entire system forcing me to do a 3 finger reboot.
     Any suggestions on where to start troubleshooting?

     If you have a SCSI interface card plugged into your GS, you may have run into a bug which seems to affect setting up of the diskette port. (See the next question and answer.)

     Try cleaning the heads using a Head Cleaner Diskette, such as a paper diskette + cleaning solution kit from Radio Shack. (See Q&A 004.)

     In a few rare cases, a drive may actually have globs of dust inside which end up interferring with its operation. You can shine a flashlight into the slot to check for a heavy dust buildup. The safest way to clean out dust is to open the case and the drive and remove the dust. However, you can try inserting a small cheap plastic artist's paintbrush (slightly dampened) into the slot and, with a flashlight, _lightly_ sweeping around to pick up dust. ("Lightly" means you do not push or snag on anything, 

especially the R/W heads.) Blow into the slot and do another sweep with your brush.

     If cleaning does not seem to help, try wiggling the drive cable while attempting to CAT a known-good, unprotected diskette in the drive. If wiggling helps, you are likely to have a bad cable or a GS plug with a loose connection to the motherboard.

     Try formatting a diskette. A drive which can format and R/W diskettes it has recently formatted but cannot read most other diskettes probably has heads which have become misaligned.

     Set your boot Slot to Slot 5 and try power-up booting a couple bootable ProDOS diskettes known to be in good condition. If you can boot a variety of disketts, including commercial game, etc. diskettes, the odds are pretty good that your drive is okay.

     A 3.5" drive that, after cleaning, cannot boot known-good diskettes is likely to have screwed-up heads. However, it's a good idea to try unplugging and re-plugging the drive (with the computer OFF) and, then, try another boot.

     If you have a 5.25" drive attached, boot ProDOS from the 5.25" drive and try some CAT's of non-protected known good 3.5" diskettes in the 3.5" drive. As earlier, do the cable wiggling test while attempting the CAT's.

     A very good test is to try out the drive on a friend's IIgs or IIc+. If it continues to bomb, it is likely to have R/W heads which have become badly misaligned, heads which are badly worn, or heads which have been partially dislodged from the mountings. (The 3.5" drive's heads are held in place by springy metal sheets. Unlike the mounting for the 5.25" Disk ][ head, these are fairly delicate. If anyone has tried cleaning the heads by sticking in an alcohol swab and 'swishing around', there is a good c

hance the head mountings are messed up.)

     Shops which replace heads are fairly rare. I had this done a few years ago and the drive still works fine. However the charge is around $80. It is cheaper and easier to get a good 2nd-hand drive at a swap-meet. You can, also, look for a bargain Mac drive and do a "transplant" as described by Steve Buggie in the Winter 1996 issue of II Alive.

     Steve Buggie is a good source of information on drive repairs. Check out some of his recent posts to this newsgroup.

----------------------


010- Sometimes the 3.5" drives on my GS do not function correctly.
     This started after adding a SCSI interface card.
     Is there a fix?

     This problem seems to crop up from time to time, especially when a SCSI interface is present and when no device is connected and recognized on the SCSI chain. (For example, you may have only a Zip Drive connected to your SCSI interface; but, it is not powered ON or no Zip disk is inserted.)

     Evidently, something (e.g. a register or softswitch) involved in the usual GS power-up routine relating to on-line devices gets messed up. Arranging to have some active, on-line device on the SCSI chain (or removing the SCSI card) seems to help reduce frequency of the problem.

     A nearly certain fix is inserting a 3.5" diskette into Drive 1 before or just after power-up. This usually forces recognition of 3.5" diskette drives and enables correct functioning.

----------------------------


011- Both of my Disk ]['s come on when booting! How can I fix this?

     Basically, it sounds like Drive 2 does not know when to stay OFF. There are three fairly high-probability places where a glitch may cause this to happen:

 1. The 74LS132 on the Disk ][ Controller card may have a blown gate or some pins may be making poor or no contact. Try unplugging and re-socketing the IC. This usually takes care of bad contact problems. (Or, you can replace the 74LS132 IC with another 74LS132 or 74132. A 74LS00 or 7400 may work, too.) Also unplug and re-socket the 9334 and 556.

 2. The ULN2003 IC on the Drive 2 main circuit board may have a bad gate or may have developed some poor pin-to-socket contacts. Remove the drive cover. Unplug and re-socket the ULN2003 IC. (Replacing a blown ULN2003 should not be too difficult. Both Mouser and Newark carry the IC.)

 3. Drive 2's cable may have developed a short between pins 14 and 16. Mark the position of the cable at the Controller card and at the Drive 2 circuit board and unplug the cable at each end. Use an Ohm meter to check for shorts between adjacent pins. If you find a short between 14 and any other pin you can try repairing the cable or cutting out line 14 and running a new lead; or you can get a replacement cable.

___________________________



From: Rubywand

012- In connecting a second Disk II drive to my Disk II card I
     misaligned the connectors. The result upon turning it on was a
     static-like clicking noise. Now I can't load anything from
     disk. Is the Disk II card dead? Are the IIe and Drives all
     right?

     Try removing the drive which was connected incorrectly. If your system boots from the remaining drive (connected in the Drive One position), this is a fairly good indication that the Disk II card and IIe are okay and that the removed drive is messed up.

     If it looks like a drive is bad, remove the cover and inspect the drive's main circuit board for blown components. If nothing obvious shows up, a decent fix try is to replace the 74LS125 IC on the drive's main circuit board. (Also, see Q&A 013.)

----------------------------


From: Ryan Underwood

     I accidentally offset a row of pins on the //e disk controller card when plugging one of the drives in. Snap, crackle... you get the picture. I opened up my freshly fried Disk II, and in the center of the board there is a 74LS125 that is blown. Replaced it (it was socketed) with the same chip from another Disk II, and voila! it works again.

     I would reasonably assume that misaligning the drive connector on the controller is what blew the 74LS125 in several Apple II drives before they got to me. Note that while the genuine Apple Disk II simply lights the LED and doesn't move the head at all when this IC was blown, a Mitac drive actually ate disks. So any number of dead Apple II drives with different symptoms could have a blown 74LS125.

___________________________



From: Rubywand

013- Last night a sound like a shotgun going off came from my 5.25"
     Disk ][ drive. Now it doesn't work. How can I fix it?

     The noise was probably an electrolytic capacitor exploding. Sometimes, these develop internal shorts, heat up, and blow (kind of like a sealed can of beans on a campfire).

     The fix is to remove the drive cover and replace the blown capacitor. (Look for a small can-like component with goo and/or shredded foil coming from it.) Circuit board markings should help identify the component. Here are some suggested replacement values:

C2 (on +12V line):  220uF-500uF at 20V-50V
C4 (on +5V line):    470uF-500uF at 10V-25V
C5 (on -12V line):  10uF-50uF at 20V-50V

     If there is some difficulty identifying the blown capacitor, replace it with a 500uF unit rated at 20V-50V.

     Before removing the bad capacitor, note which lead is connected to the outside 'can' part and mark the circuit board where this lead is connected. This is the Negative side of the capacitor. When installing the new capacitor make sure its negative lead goes to the marked point on the circuit board.

____________________________



From:  Wayne Stewart

014- Recently I picked up two 3.5" drives at a swap meet-- a
     Uni-disk and a Laser 128 drive. I've tried cleaning the
     heads; but, neither works with my IIc. What's the problem?

     The 3.5 unidisk won't work on the earlier IIc unless the IIc has had a ROM upgrade. The Laser 3.5 is actually a Macintosh drive with the addition of an eject button. It isn't compatible with any Apple II unless it has a special controller card, which of course a IIc doesn't.

____________________________



From: Stephen Buggie

015- Can I replace a bombed Apple II 3.5" drive mechanism with
     one from a Mac?

     Yes. 3.5" drive mechanisms are cheaply and abundantly available from the Macintosh world. Although Apple II users have increased their interest in 3.5" drives, these drives have declined in their utility for Mac users who have shifted to hard drives, CD-ROM, and flopticals.  Few Mac owners have use for the external 3.5" drive any more; if they have not yet discarded their external 3.5" drive, it is now in storage.


     MAC AND APPLE II 3.5" DRIVES: SIMILARITIES/DIFFERENCES

     The basic Sony 3.5" mechanism is shared by Mac and Apple II.  It stores 800K of data on a two-sided disk.  Unlike the IBM version with its constant rotational speed, Mac/Apple II drives maintain constant head velocity by varying the rotational speed as the head assembly approaches towards or moves away from the disk hub.  Mac and Apple II drives differ in their track sectoring arrangements, so disks cannot be read directly without special translational software.  The opportunity for compatible disk sh

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