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AuthorTopic: External floppy port does not work, A2000. Anyone know what to check for?  (Read 1713 times)

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Offline Malakie

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External floppy port does not work, A2000.  Anyone know what to check for?   Have tried both the A1010 and an A1011 as well as two 3rd party drives. None of them do anything.  So best guess is the port has a problem but not sure where or what to look for.. The odd thing is the boot menu and other tools show DF2 as there and available...
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Offline Pat the Cat

Could be fuses F3 and F4, going to pins 23 and 12 of the floppy port.

Without those, no power for motor (+12V on F3 and pin 23) or circuit inside the external drive (+5V on F4 pin 12) of the floppy port.

This is from a Rev 6 schematic though.

https://www.amigawiki.org/dnl/schematics/A2000_R6.pdf

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Offline Malakie

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Could be fuses F3 and F4, going to pins 23 and 12 of the floppy port.

Without those, no power for motor (+12V on F3 and pin 23) or circuit inside the external drive (+5V on F4 pin 12) of the floppy port.

This is from a Rev 6 schematic though.

https://www.amigawiki.org/dnl/schematics/A2000_R6.pdf


Thanks will test them out ...  Would that be the same for any Amiga too?
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Offline Pat the Cat

They might have different numbers but they'd still begin with F for fuse and connect to the same pins on the external floppy connector.
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Offline Pat the Cat

Actually after having looked at a Rev 4.4 A2000 motherboard, they don't begin with F.

Rev 6 shows up F3 and F4 very nicely just above the 8520 CIA chips, but on Rev 4.4 they begin with C.

http://amiga.resource.cx/photos/photo2.pl?id=a2000&pg=5&res=med&lang=en

http://amiga.resource.cx/photos/a2000,3

Although similar principle, limiting current to the port in case of a short, the fuse dies rather than the whole computer.

I checked the back of the boards, they both run up to EMI320 and EMI321 leading to pins 12 and 23.
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Offline Malakie

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Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #5 on: December 22, 2021, 04:26:18 PM »
Actually after having looked at a Rev 4.4 A2000 motherboard, they don't begin with F.

Rev 6 shows up F3 and F4 very nicely just above the 8520 CIA chips, but on Rev 4.4 they begin with C.

http://amiga.resource.cx/photos/photo2.pl?id=a2000&pg=5&res=med&lang=en

http://amiga.resource.cx/photos/a2000,3

Although similar principle, limiting current to the port in case of a short, the fuse dies rather than the whole computer.

I checked the back of the boards, they both run up to EMI320 and EMI321 leading to pins 12 and 23.




Thanks..


Am putting aside the other A2000 I have been trying to get 3.2 to work on properly because it has become a project of frustration..  So back to this unit with the floppy drives problem..

Question, what about if NONE of the floppies will access.   I did a bit more testing and I did not realize the two internal floppies are not accessing either.  They appear to have power and the LED's come up but neither will boot.  The external drive port, is dead, no power.   Would these same fuses cause the internal drives to fail also?   I know there is something I am forgetting and the 8520's as well related to all this and it keeps popping into my head but I can't remember what exactly my brain is trying to bring back up about that...



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Offline Pat the Cat

Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #6 on: December 22, 2021, 06:03:18 PM »
Disconnect external floppies before proceeding, If they aren't getting power they are indeed problematic.

Check you have a 12V supply on the internal floppy connector - no power, no motor action.

If so, try swapping the 8520s (CIA) chips to see if behaviour changes.

Very often on neglected drives, the "disk inserted" switch gets blocked up with dirt. Use WD40 and make sure the thing can press om when a floppy is inserted.
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Offline Malakie

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Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #7 on: December 22, 2021, 08:20:27 PM »
Disconnect external floppies before proceeding, If they aren't getting power they are indeed problematic.

Check you have a 12V supply on the internal floppy connector - no power, no motor action.

If so, try swapping the 8520s (CIA) chips to see if behaviour changes.

Very often on neglected drives, the "disk inserted" switch gets blocked up with dirt. Use WD40 and make sure the thing can press om when a floppy is inserted.


In this case it is ALL three drives, both internal and external.  And that 8520 idea is what my brain was probably trying to remember.. I knew something about 8520's was in the chain, just taking time to bring the brain cells back...   I know I am forgetting one other piece of the puzzle but hopefully, that comes back as I work on this other machine now.


Thanks for the assist.
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Offline Steady

Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #8 on: December 22, 2021, 11:34:44 PM »
Maybe this is linked to your problem with your timer running too fast.
 

Offline Malakie

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Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #9 on: December 22, 2021, 11:51:39 PM »
Maybe this is linked to your problem with your timer running too fast.


No this is a different machine.. That problem was on the other one I put aside with the 3.2 HD problems.


This one is another one that I knew was having a problem with the external floppy drive.. It is a rev 6.3.   But I now know the problem is more serious than a blown 8520 because it just smoked one of my Gotek drives.

I have an extra floppy drive assembly that has a floppy drive for DF0: and a Gotek for DF1:  It is (was) a known good all around power supply and drive setup for testing only that I use.   I moved the unit in this machine out, and plugged this one in because neither floppy on it would boot the computer.. lots of read write issues even for known good disks.


Well, plugged it in (and before someone says anything, yes I always double check cables etc), added power and at first everything appeared to be ok.. Got the kickstart screen and it say there for a good minute.... and then suddenly SMOKE came billowing out of the Gotek.   Suffice it to say it's toast.   It still actually shows the OLED function but plugging in a USB media now does not work.  Dunno yet if I can repair it but that's low on the list as I had another one.

The floppy on my test rig does boot the machine fine however.  So either the p/s or both floppies have an issue that came with this machine.  For now I will keep the test rig in this until I get it working fully.


  I have never seen something like this before.. it's like power fed back into the unit somehow... or it was a coincidence that something just happen to fail while plugged into this board, which has a bad external floppy port already.

I pulled the Gotek, installed another and so far, it appears to be ok in that regard, so I have no idea what caused that.  But my test P/S/Floppy/Gotek is functional again at least.   Now I need to figure out what the hell the problem is with this external port.  I swapped 8520's so now I need to look deeper for a problem and will test the fusable links that Pat the Cat listed next..



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Offline Pat the Cat

Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #10 on: December 23, 2021, 02:18:00 AM »
<sigh>

I did recommend changing the fuses and not trying the externals until you'd got an internal drive working.

When Mr chip has no power source but does have active high (+5) data lines, guess where it tries to draw power from?

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Offline Pat the Cat

Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #11 on: December 23, 2021, 02:48:23 AM »
Might be worth checking out the internal floppy cable too.

Check for bridges between connections. A short on that can cause issues with the whole floppy system.

They are usually very scruffy at best, and often get trapped when fitting/removing expansions.
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Offline Pat the Cat

Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #12 on: December 23, 2021, 11:27:32 AM »
The Gotek might be saved with a new 3.3V regulator for the microcontroller (STM32 I think for the older ones).

I have done with successfully that an over volted Arduino, Worth a shot.

However tracking down a new STM32 might be tricky.

Hopefully the regulator failed in time and didn't damage that or the USB stick.
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Offline Malakie

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Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #13 on: December 23, 2021, 09:13:39 PM »
The Gotek might be saved with a new 3.3V regulator for the microcontroller (STM32 I think for the older ones).

I have done with successfully that an over volted Arduino, Worth a shot.

However tracking down a new STM32 might be tricky.

Hopefully the regulator failed in time and didn't damage that or the USB stick.


It's Christmas!  I need some happy right now.. Man I hope it did not damage all that!  Whatever it did smoked though so once I open it, it should be obvious.. . 
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Offline Pat the Cat

Re: External floppy port does not work, A2000. Anyone know what to check for?
« Reply #14 on: December 23, 2021, 10:57:00 PM »
50-50 chance I reckon. 3.3V regulators do odd things with floaty grounds.

I'm not convinced having a separate power supply is a great idea for floppies. On an A2000 at any rate.

It's not like AmigaDos uses more than 2 floppy drives at a time, and that's just for copying a whole disk from one to the other. Generally only one is in use for reading. Depends how quick you eject and insert disks mostly.

As a rule of thumb, I turn on external expansions before powering up the Amiga.

External floppies going pear shaped can damage pull up resistors on the floppy circuitry. Usually the problems start by the power to the external floppy being shorted out with a different connector.

You have to allow yourself to make mistakes and learn from them with renovation.

Anyhow, if you start with getting DF0: internally working, you can use the external port to "snoop" on the different signals with a logic probe. In that case, having no power on the external floppy port actually works in your favor.
« Last Edit: December 23, 2021, 11:53:37 PM by Pat the Cat »
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