A few days ago I had the opportunity to work on one of my friends external Amiga floppy drive.
As I had no experience with such external drives electronics before, I was learning on the fly.
I knew that such external drive is having quite a simple additional board so I was thinking that it can't be that hard.
Well, this one was….
This drive was actually modified and because of that I had no clue how should I configure/jumper it at all, nor why this modification was made.
It did not look like a factory mod, but that also could not be excluded.
The strangest part was that it had the disk ready signal on pin 6. (I was even thinking that the purpose was to make it not compatible with any drive.)
This modification had additive and reductive components also.
2 jumper wire was added and a resistor.
The reductive part was disabling the transistor on the board by cutting two traces.
Also 2 legs were cut away from the rest of the electronics on the 74LS74 logic chip. Same two that had the green jumper wires.
Also I have discovered some cuts around J3 and J4 and actually that made zero sense to me… These were also not connected originally, so...
Because of this I would bet that this mod was not a factory mod.
After getting more and more familiar with it I was brave enough to plug it in to my only and precious Amiga 500.
Yepp, it did not do much… At least it did not kill my Amiga 500!
The drive gave disk insert signal, but nothing else.
Did not move the head.
I was like, ok, this mod probably works, but the drive itself is dead.
I have previously modified a PC drive to have a spare drive for my Amiga 500. A Samsung it was. Decided to try it with that one as that works for sure.
It worked. Partially…
It was reading discs actually, but did not react on disk change. Also did not give ready signal. I mean the drive itself did but was not routed by the case.
I knew that the previous drive was wired differently. So also modified my Samsung that way. (Ready signal to pin 6)
Still did not work.
At this point I have spent at least a day with it and I felt totally lost….
Decided to be more precise and ordered the logic chips for.
When chips arrived, I have restarted the work on it.
Socketed the chips, so I could test easy.
Unfortunately swapping the chips also did not change any. But at least I could have excluded 2 out of the 3. (for one the supplier sent me a different type so I could not test on that.)
Also I have lost confidence on the signal my drive was giving.
I was estimating that the cases electronics is expecting different signal somehow, so I was thinking it could be nice to try other drives also.
Again stopped here.
My friend sent me another Sony to try. So I was waiting for it to arrive.
It was a PC drive. so I had to modify.
No luck still.
Decided to undo the mod on the case it came with.
Removing the resistor, the two jumper wires were easy.
It was also not very hard to reconnect the transistor to where it belongs to.
Also there were those two cuts on the 74LS74 ( The two pins that two jumper wires were connected to.)
But had no clue how to jumper it still. (At this point I only knew what J1 does.)
Connected the drive and yes it was working, but the disk change and ready signals.
Shorted J1 and J2 and at that point the drive started to behave better!
It have even started to do that familiar clicking sound!
It was reading writing and started to be sensing disk changes.
I was thinking that it is done.
I was to try to copy some, using X-Copy and well that failed.
Loaded up my test software and it was telling me that I still don’t have the drive ready signal….
Looks like only some software is actually checking on this, but still… Is bad.
Other than this the drive was testing ok.
I was going back to the floppy drive itself.
Did verify my previous work I have done on it.
I
did cut the trace on pin 34 and pin 2. that was correct. (also on pin 6
as that is not used on the Amiga and was not sure what it does on a PC
dive.)
I have wired the lead from pin 34 to pin 2. Correct it was.
Also have wired the lead from pin 2 to 34. Also correct.
I was again close to be hitting my table with my head….
I was like ok, so I did the wiring as supposed to be. But is the signal there?
I
have soldiered some test wires on, and started to learn on how these
signals are supposed to be behaving so I can verify. (Googled some on
the topic)
As I found these signals are not at all complicated and
are actually quite binary. Like there is 5V or no 5V. So is one or zero.
That is it.
That was good, because I only had a multimeter but no oscilloscope.
I was checking on the drive ready signal and it was not there at all! (If is HIGH then is not ready. If LOW is ready)
This
was a quite useful finding , because I knew that this time it is not
the board in the case,but the drive itself causing the issue.
Ok so
it is not there. This is a PC drive and as I have learned by doing
further reading/learning about these drives, found that PCs were
actually not using this signal at all so probably manufacturers were not
focusing on wiring it out correctly.
But as it is part of the standard, the controller chip at least should have it.
I was reading the entire internet, searching for this drive I had in my hand.
Almost all already modified ones I have found was wired the same way I did, but one!
There I have found the ready signal wired differently.
I was also able to find it on the drive I had in my hands. Is on the below picture:
That only one webpage have helped me. Worked!
That signal was behaving exactly I have learned it should.
At that moment, I could not decide if I am more happy than proud or more proud than happy.
Ok, one thing was still missing.
PC drives are capable of handling HD disks.
There is a switch reading a hole on the disk that is defining if the inserted disk is HD or not.
So this switch had to be checked if I have to short it or disconnect it fixed.
So
even if HD disk is inserted it will still be handled as DD disk. (If
not, Amiga will not be able to handle at all and would error out.)
As I have found a short was needed, so I have left the switch in place like so.
After this, I have started to put everything together again, Into its case.
I was careful luckily, because this case was also having some design flaws.
One was that two mounting screws are too close to leads on the main board!
I was afraid that if I screw it in this way, it might be casing shorts. So I have added paper washers for two.
Also when screwing the case together, one screw felt strange.
I
took the drive apart again and discovered that this screw is actually
touching the soldier points of the capacitor! (Might be these are not
the factory screws. You never know.)
I have used a shorter screw instead.
After all this, finally it all was in its case working!
I
only took it apart again a day later for a final cleaning and a front
panel swap on the drive to a less yellowed one. (The original Sony
drives front panel was identical and what is even more important, is
that it was not yellowed at all.)
Also cleaned the head carefully.
After cleaning was done and again in one piece, I have made the usual after repair stress tests.
First checked in Workbench.
At this point I gave in for my curiosity.
I have never had the opportunity to daisy chain floppy drives on the Amiga before witch I was very curious for, so I did!
After all 3 drives I could try together were showing ok in WB, I made some copy jobs using X-Copy.
I have even made a simultaneous copy from one disk to two others at once, in one go.
Also formatting 3 disks at once!
It was a lots of fun!
Specially because I felt like, this was one of my rewards for the good work I have done!
But it wasn't.
Other reward I was preparing for, was supposed to be my friend smiling when using.
But, my friend tricked me and decided to donate this device to me!
This I could not handle until now.
It is honored feeling.
Is
now fully operational. And while I am writing this summary, My
daughters are playing Bubble And Squeak on the Amiga, that is able to
make use of two drives, so I don’t have to continuously swap the disks
for them.
