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Apple II Europlus recuperation project

FelisSapien

Member
Joined
Feb 18, 2021
Messages
18
Location
Birmingham, UK
Hi all, since my last posts relating to the PSU I've had some fun getting the computer up and running. I'm now at a stage where as far as I can tell things are pretty good. I can boot to BASIC. I've verified the ROM contents. Basic memory tests pass. I'm feeling pretty chipper about things...

So now I turn my attention to the disk drives - I mean, I'll want to read and write data at some point, right?

Included in the bundle of bits I received are two disk II interface cards. One I can plug in and seems good. The other causes boot to fail. The only thing that seems odd is that the 74LS323 marked on the card reports to be a 74LS299 (according to Xgpro). The markings on the chips show AMD AM75LS23PC. Both fail logic tests in the same way. If I swap the chips between cards then the good card is still good and the bad still bad. So possibly there’s no issue here? I will order some spare chips and see what happens. I'm mostly ignoring the bad card for now.

If I use the good card and attach a drive then things start out looking reasonably normal. The disk spins, not crazy fast. Heads are moved back towards track 0 - I hear clicking for a second or two. But when I insert a disk… Nothing. Both drives behave in the same way.

I’ve tested 74LS125 on the analogue board (Xgpro) and the chip reports good. Flipping the drives over the speed visually looks about right. One thing that does look off, is the position of the track 0 marker on the cam. The technical manual I’m looking at suggests that this should rest just right of the cam follower. On both my drives it’s some way off, well in to ‘bad’ territory. I would adjust this but my gorilla brain can not make sense of the instructions given by the manual, which read:

To adjust the drive, unscrew the small screw (near the head on the sliding limiter - my interpretation) and move the cam. Be very careful, as this movement tends to damage screw threads all too easily. Once you have the cam adjusted, carefully tighten the screw again.

Now, I think I understand the words… but in practice I can’t make any change in where the track 0 marker is. Surely I’m missing something really obvious? I’m unable to find any clearer instructions (or videos) on this calibration step. I did locate some alternate instructions - The Basic DISK II Pages on the Wayback Machine but I can make no more sense of those.

Can anyone shed any light on what I’m supposed to be doing? Or offer other advice? Either on how to complete calibration or in further areas of investigation. I guess all the disks I have could be bad. At the moment I'm not sure I've a way to test this.

Onto general comments: At the moment the only way I have to get software to the computer is via the cassette port. I have a Floppy Emu on it’s way so at some point in the future I’ll be able to get s/w loaded on this computer. Am I right in thinking I need 64K of memory to use ADTPro? I recently missed a Microsoft memory card on eBay but will keep an eye out and bid harder next time.

I hope the above isn't too much of a ramble and makes some kind of sense. Thanks for the assistance - Carl
 
I've never realigned drive heads, so s.o. else has to help you there.

The LS323 and LS299 are very similar, only differing in the reset signal being synchronous vs asynchronous. For the disk II interface it probably doesn't even matter. My guess is both would work anyway.

You mentioned one card doesn't boot. But then you say none of your drives work. So you cannot boot from any disk. What's the difference between the cards then - is the system completely dead when you plug the bad card?
 
What's the difference between the cards then - is the system completely dead when you plug the bad card?
yup, with the bad card I get a screen full of random blocks at power up.

To be clearer on my current test case. I‘m using the controller card I can boot with. Which ever drive I’m testimy is plugged into the drive 1 port.

Something else I tried was to swap the analogue cards of the drives. No difference.
 
Remove the P5 PROM from the problematic card and see if the machine boots when the card (without P5) is plugged. My guess is, it will boot then (but of course not access the drive). If it boots, then either the P5 ROM is bad. Or, if you have already excluded that by swapping the ROM with the other card, then there is a connection issue (likely data or address bus not having proper contact). Use a multimeter to check each pin from the P5 socket to the appropriate bus connector fingers.

If the machine is still dead with P5 ROM removed, then also remove the LS323 and try again. The LS323 could also block the machine if the R/W or DEVICE_SELECT signal were not properly connected.

If the machine still wouldn't boot with P5+LS323 removed, then you have a dead-short on the card affecting some data/address bus or control signals.
 
Quick update... unplugged the P5 ROM from the bad card and found no change. Swapped out P5 and LS323 (LS299) between cards and again no change in the behaviour of either card. So those chips didn't seem to be to blame. Checked traces on the bad card and found no obvious break in continuity.

I don't like doing this generally but with so few ICs - all socketed, I went around swapping ICs from the good card to the bad and found the 74LS259 to be the issue. The bad chip tests ok in the TL866 but I can create switch the issue between both cards by swapping this chip. Result!

I wasn't necessarily looking to resolve this partuicular issue right now but this seems such a simple fix.

For the other issues I've a Floppy Emu and (hopefully) a RAM card on the way. I can hopefully better diagnose any issues with the drives once I can get some software on to the machine.

Cheers!
 
If you have ever installed the ribbon cable even one pin off, then the analog board on the drive will be damaged and it will become an automatic disk eraser. Any disk you insert after that point will have track 0 erased. It's frustrating to troubleshoot after that, but it's usually one specific chip on the drive that gets damaged... You can search for this- it's very very common.
 
Ok... I now have two working Disk Interface cards - Lucky me! ;) I also received my Floppy Emu. This works fine with both interface cards so the issues there is hopefully passed.

On to the disk drives. I'm only working on one at the moment. With the Apex II speed test the drive seems unable to spin to speed. Adjusting the pot on the side of the drive decreases/increases the speed - I can hear the difference. But the speed test reports some crazy negative value. Later on, when I get a little more time I'll flip the drive over and check the condition of the belt. From memory it didn't seem crazy bad.

I'll scour the web and follow any obvious leads. I'll report back but now I have the Floppy Emu I might try to enjoy the computer for a while before getting stuck in deeply.
 
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