External floppy port does not work, A2000. Anyone know what to check for?

[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

[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.

[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.

[Pat the Cat]

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.

[Pat the Cat]

<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?

[Pat the Cat]

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.

[Pat the Cat]

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.

[Pat the Cat]

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.

[Pat the Cat]

If you are having trouble finding replacement fuses, according to this;-

https://pmsoft.nl/amiga/amiga-parts-chips.html

You need 4A through hole pico fuses. Voltage not really relevant so long as over 12V. 125V frequently fitted.

(You can probably get away with 2A),

Nintendo fitted similar in the Gameboy, don't pay more than a buck each (hopefully less).

[Pat the Cat]

Mouser have if you can't find on Amazon. More expensive though.

Video, serial and joystick ports also have one each, so buying a bag of 10 isn't a terrible idea.

[Pat the Cat]

If you search on

Pico fuse 4A

You will find them on amazon and eBay (Ebay might have a local supplier).

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=pico+fuse+4A&_sacat=0

https://www.amazon.com/s?k=pico+fuse+4A&crid=166G77NXHKM26&sprefix=pico+fuse+4a%2Caps%2C333&ref=nb_sb_noss

These links assume the buyer is in the UK (my point of view) rather than Michigan (your point of view).

But they are the American website stores.

[Pat the Cat]

You don't HAVE to have floppies inside an A2000 at all. Plus, duplicating software can drive all four drives, even if the Os doesn't behave that way.

Not everybody uses the power pins on external ports for their intended use either.

[Pat the Cat]

Anyway, if you want to go 500 milli amp (still overkill);-


https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=pico+fuse+500&_sacat=0&LH_TitleDesc=0&_odkw=pico+fuse+4A&_osacat=0

EDIT: Better go 1 Amp, tech reference manual reports surge current of 540mA.

https://www.opweb.de/english/company/Commodore/Amiga_A2000

(Amazon too screwy, started mixing in 500 Amp fusss).


You might consider fitting a thermal cut off fuse instead. They don't blow, they just shut off with an over current (more recent technology than pico fuse).