Repair an Amiga mouse (and identifying mystery component)

[Turrican3]

@Ian.M

That seems brilliant!
Unfortunately right now I don't have any Kynar wire nor any suitable motor.

I think I could steal the breadboard trick suggestion though so I can fiddle with resistor values.

PS: better PCB picture coming in seconds

[Turrican3]

Here's the PCB picture in good quality
(feel free to click to enlarge and get the full size image)

[Ian.M]

A motor would be better, and much easier to use for testing the duty cycle, but you could also put a long wide ribbon or strip of un-gummed paper tape under the mouse (with the ball in place) and pull it out at as steady a speed as you can manage.

The next thing to do is either to print out that new photo A4 size, or use a paint program to edit it, and start labelling the signals (look in the Amiga manual for the mouse port pinout and use a DMM on continuity to identify each wire), and mark on it symbols and values for the top side components. If you have any difficulty identifying them post a high quality topside photo with the wires held out of the way.  The electrolytic capacitor (little aluminum can in plastic sleeve) should have its value,and working voltage printed on its sleeve, together with a stripe to identify its negative lead.

[Turrican3]

The next thing to do is either to print out that new photo A4 size, or use a paint program to edit it, and start labelling the signals (look in the Amiga manual for the mouse port pinout and use a DMM on continuity to identify each wire), and mark on it symbols and values for the top side components.

Seems another great suggestion, that would likely help me with the schematic as well!

(I already have the pinout labeled and continuity tested from the PCB to the connector, still a lot of work to do of course)

[Turrican3]

Hey guys I'm back with a VERY good update!

(I'm still working on the schematic by the way)

So, by adding the 470 ohm resistors in parallel to the 271 labelled ones, as suggested by @Kleinstein, I'm happy to confirm that both X and Y axis are now working (apparently) flawlessly! Tomorrow I should receive my scope so that I can have a visual confirmation of the quadrature signals being ok, but I'd say this is already a significant step forward.

Now what?

Should I try to source replacement IR LEDs?
Or, should I just leave the current LEDs in place and just purchase different valued smd resistors (which value? the parallel between 270 and 470 or what?) instead?

[Kleinstein]

It the parallel resistors solve the problem, I see no reason to change the LEDs.  I would even consider leaving the parallel resistor construction.

[Turrican3]

I'm a bit worried about size, there's not a lot of space there.

Perhaps the other option then, i.e. replacing the smd resistors with an adequate, different value?

[Tomorokoshi]

I'm a bit worried about size, there's not a lot of space there.

Perhaps the other option then, i.e. replacing the smd resistors with an adequate, different value?

For boards like when replacing parts it is very easy to lift tracks and pads. Can you show a picture of the modified board?

[Turrican3]

Absolutely!

But it was meant to be a test so it's just the photo posted before, plus 4 regular resistors hanging around the solder side of the PCB.

Would it be useful nonetheless?

[Tomorokoshi]

Absolutely!

But it was meant to be a test so it's just the photo posted before, plus 4 regular resistors hanging around the solder side of the PCB.

Would it be useful nonetheless?

Sure, got it. From that view if access is only available on the bottom side of the board then replacing the components with the equivalent part should be fine. Those tracks look quite robust.

[Turrican3]

Great!

So what about the value then? Parallel of 270 and 470 Ohms as I guessed before or what?

[Kleinstein]

The exact value of the resistance is not that critical. My estimate would be 180 ohms, as a standard value. 220 Ohms may work too, but it is not such a big step down from 270 ohms.

I would expect that the space should be OK for 2x0805 stacked.

[Turrican3]

Awesome, thanks again.

I don't think I have any brand new smd resistor available right now, but I own a decent number of non working boards, I'm quite confident something must be waiting to be desoldered and brought to (new) life.

[Turrican3]

Sorry for the huge delay, I'm still waiting for the delivery of the SMD resistors (found nothing inside my small broken electronics bag/junkyard, and brand new parts are not available in my area unfortunately, so I had to resort to ebay) so here's at least I can share what I see for Horizontal and Vertical quadrature signals with the standard resistors in parallel with the original parts as suggested.

As I said, the mouse currently seem to work flawlessly, I guess the quadrature signals are... ok-ish?