Amiga600 Floppy led keeps lighting up?

[Castellen]

The machine is working as it should, only that the drive led is constantly active. And I have absolutely no idea on to what I should look for. Any suggestions?

The floppy drive LED is driven from the MTR0 signal, the same signal that tells the drive motor to switch on.  Meaning that while the line is low to activate the motor on the internal drive, the LED turns on as well.

So the question is that when the floppy drive LED is on, then is the internal drive motor on as well?  It's very quiet and you may have to put your ear directly on the A600 to hear it.

If the drive motor is turning on and off as it should but the LED remains on, then look at the LED driver circuit.  Which is simply a PNP transistor, Q632.  The circuit is configured so when MTR0 is low, drawing current from Q632 base, it causes the transistor to conduct 5V to drive the LED.

If the transistor has been damaged, it'll usually fail short circuit, which could explain the LED being permanently on.

In which case the solution is to replace Q632.  The original device is a 2N3906 or MMBT3906.  I don't have one in front of me, but it's probably a SOT-23 package.  i.e. the slightly larger surface mount type, not the smaller SOT-323.  Any other general purpose PNP transistor in the same package will be fine as well, e.g. BC857. They're easy to source and cost a few cents each.

[Castellen]

New issue have turned up. The bluish "film" on the RGB output have returned. (the issue it was recapped for)
Yet as the bluish color have returned, the floppy led issue have resolved it self for some odd reason.
Now I really need to get that internal scandoubler, as I can live with bad signal from the RGB output.
The Floppy led issue might return after some time. I don't know... :-(

Since the floppy drive LED is working intermittently, then it's not a problem with short circuit Q632. Though if it has been exposed to leaking capacitor electrolyte in the past, then it can cause unusual things to happen.  If the area around Q632 has been visibly corroded (solder joints not shiny and silver) then I'd suggest replacing Q632 anyway.  Very unlikely to be a resistor problem.

Failing that, you'll need to take some measurements while it's in a faulty state in order to work out where the problem is.


As for the (intermittent) discoloured RGB video, the most common cause of this is damaged transistors Q321, Q232, Q233 which are the RGB signal output drivers.  Usually as a result of leaked capacitors.  I'd suggest replacing all three transistors.  They're NPN devices, so different from Q632 driving the floppy LED.  Originals are 2N3904, but I expect the likes of a BC847 would be a drop-in replacement.

If that's outside of your abilities, contact me for a repair estimate.