Hello,
Recently, I've gotten into retrocomputing by getting my hands on an Apple //e. It's been working fine while I've been having fun with it for the last few months, but I started to get some problems with the duodisk drive my computer came with. Initially I was getting "Unable to load ProDOS" errors while trying to read ProDOS formatted disks, but it would still read DOS 3.3 disks just fine. I tried to use some repair techniques I read about such as swapping disk drives, putting the card in different slots and reseating chips on the Duodisk analog board, but this didn't change the drives behaviors at all. Then, when I was swapping connectors on the disk drives, I accidentally replugged it to the computer while the it was still on, resulting in spontaneous drive activity and the possible death of the analog board. Surprisingly, the drives would still turn on, only now there was no R/W head movement, no drive activity lights, and it would spin indefinitely. However, the drive indicator lights would turn on for a second when I powered down the computer.
I decided to replace some IC's on the analog board (74LS125A, MC3470AP, and CA3141E) that were specified in the Duodisk repair manual, but that didn't do anything. I then replaced the analog board and controller card with some spares I had, but again didn't change the behavior. I finally experimented with different combinations of the analog boards and cards to no avail.
I believe the problem maybe with the actual computer itself rather than the drives, but I don't have the expertise to go through and debug the computer. Do you guys know what the problem might be?
Some technical information:
-Apple //e has been upgraded to the "enhanced" version
-The original controller card was a 655-0101 and the analog board
was a 676-102. The replacement card is identical while the
replacement analog board is a 676-101.
-Both analog boards had 2 capactors snipped off to prevent the
drives from chewing disks after power cycle.
-The replacement IC's for the original analog board are DM74LS125AN, CA3141E,
and MC3470N.
-All the accessable traces on the cards and analog boards have been
tested for conductivit
I began to test my controller cards by connecting wires from the the DB-19 connector to breadboard and a multimeter. It's not as accurate as probing with logic probes or an oscilloscope, but it was quick and simple. Good(?) news is that both cards seem to act the same, except that when booting with the replacement card, pin 11 (01) is outputting 4.30V while the original card is at 0.02 volts. The 12V Pins of the connectors and the motherboards slots are also about 0.20V higher than they should be.
Here's a link to the data if anyone's interested.
Also does anyone have any schematics or repair information about Duodisks and compatible controller cards? There seems to be little to no serious documentation out there on them.
There is a schematic of the duodisk analog board here, might be useful.
http://bitsavers.trailing-edge.com/pdf/apple/disk/5_inch/
/Rob
I started to poke around the motherboard and I noticed that the HAL chip is pretty hot. Pin 37 (Q3) on the expansion slots is the only connection between the HAL and the disk controller card. I probed pin 37 with an old oscilloscope and I received a signal but I'm not sure if it's good or not.
Can a bad HAL cause the duodisk to malfunction?
you should have started with this page :L
http://www.appleii-box.de/H084_9_AppleIIDiskService9.htm
and you should also have started reading at this pages too:
http://www.appleii-box.de/H084_1_AppleIIDiskService1.htm
you started with mismatch of speed alignment or trackalignment
and proceeded by killing electronics
- better read first before killing more of the system....
Saw those pages a little while ago. Pretty nice and informative!
Quick question on the voltage regulators on the analog board: Is the 2nd pin supposed to be ground? I've seen this on other voltage regulators, but I get ~12V instead.
edit: pin1 also is at ~12V.
No Voltage regulator present:
small black tansistors MPSU51
and
large green parts:
B108D4M are also Transistors !
The FIRST thing I do when I have recalcitrant vintage disk drives is clean the heads. Then the cables and their connectors.
Even NOS disks shed oxide causing weird random or consistent failures.
IT WORKS!!!!
I've been breadboarding chips and I've noticed that alot of them were dead (i.e. I was getting voltage leaks from inputs). I got fed up with how many dead chips I was finding (apparently cmos chips really didn't like the hotplugging), so I decided to replace them all. And guess what, it works again!
kinda...
The stepper for the R/W head functions now, and it tries to boot off the disk, but ends up with a drive failiure (unable to load prodos). This happens with most disks, but I got a copy of Retro Fever to actually boot! I also got to the loading screen of oregon trail, but it failed.
The drive heads still need to be cleaned, and there may be some calibration that needs to occur. If anyone has any ideas, I would love to hear them.
Still easily one of the most satisfying fixes I've ever done.
If your wondering heres the chips that were replaced (or swapped):
Controller card:
Literally everything. The roms and a 74ls323 were swapped from a donor card.
Analog board:
ULN 2068 (x2)
74C86
74LS32
74LS33
74LS74
74LS125
7407
74LS02
MC3469
Some of the Duodisk drives have problems with the Apple iigs.
This inspired me and I had an idea:
Replace the Duodisk analog board with two A9M0107 analog boards.
I do not recall anyone having this idea except me.
I wish I had a IIgs...
Still love the IIe though.
I've heard the idea of somebody replacing the duodisk analog board with dual unidisk boards before, though I dont think anyone has followed through with it yet.
Lots of work and risky.