Acorn Type 1 Mouse feet

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sP1d3r
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Acorn Type 1 Mouse feet

Post by sP1d3r » Thu May 21, 2020 7:53 am

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I've found a fix for Type 1 Acorn mice with missing 'feet', or the little plastic pads on the underside of the mouse.
This also applies to Amx mice with similar parts.

Without the 'feet' the mouse won't sit level but they're not the sort of thing that you can easily buy these days.
I had some M2 plastic screws that fit the little hole for the plastic foot, which I carefully trimmed with a sharp blade to the right thickness.
There's enough clearance inside the mouse to put a nut on the screw, that's all there is to it!
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philpem
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Re: Acorn Type 1 Mouse feet

Post by philpem » Thu May 21, 2020 2:14 pm

Neat trick! I'd have never thought of doing that.

I actually found a source for the original skids (the PTFE stick-on pads) not long ago. Only available in black:

https://www.amazon.co.uk/gp/product/B06X3TXW88

£10.99 for enough to fix ten mice.

I also found these which are 7mm diameter, and possibly a better fit. Although you'll be waiting a few weeks for them to ship from Shenzhen:

https://www.ebay.co.uk/itm/6-Set-pack-H ... 3519050419

These work with the Type 2 (Logitech M-PF7) and Type 4 (RISC PC, Logitech M-PG15) mice I have on hand.

Cheers,
Phil.

sP1d3r
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Re: Acorn Type 1 Mouse feet

Post by sP1d3r » Fri May 22, 2020 8:48 am

Thanks for the info Philpem, that's useful to know.
More modern mice usually have the screws under the pads so some spares would come in useful.

Do you know what type of mouse the one in the picture is?
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Last edited by sP1d3r on Fri May 22, 2020 11:01 am, edited 1 time in total.

philpem
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Re: Acorn Type 1 Mouse feet

Post by philpem » Fri May 22, 2020 9:04 am

sP1d3r wrote:
Fri May 22, 2020 8:48 am
Thanks for the info Philpem, that's useful to know.
More modern mice usually have the screws under the pads so some spare's would come in useful.

Do you know what type of mouse the one in the picture is?
Part number AGB33 is for an A3020 according to Chris's Acorns: http://chrisacorns.computinghistory.org ... A3020.html

It's probably a Type 4, aka the "RISC PC mouse": http://chrisacorns.computinghistory.org ... Type4.html
About the least repairable variant (in my experience), they suffer from LED failures. You have to cut tracks to fit new LEDs, but that's only if the PCB hasn't failed first. In my experience some track repair (with epoxy) is almost inevitable.

Interesting you commented about screws under the skates - all the Acorn mice I've seen have screws separate to the skates.

The "Types" are shown on Chris's website:
Type 1 - http://chrisacorns.computinghistory.org ... mouse.html - original Archimedes mouse, an AMX with a 9-pin plug
Type 2 - http://chrisacorns.computinghistory.org ... Type2.html - common A3000/Archimedes mouse
Type 3 - http://chrisacorns.computinghistory.org ... Type3.html - early rev A30x0/A4000 mouse aka M-PG15
Type 4 - http://chrisacorns.computinghistory.org ... Type4.html - RISC PC and apparently late-rev A30x0

sP1d3r
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Re: Acorn Type 1 Mouse feet

Post by sP1d3r » Fri May 22, 2020 11:26 am

#-o Thanks again Philpem, it's a type 4. I'm not the original owner so I don't know anything about it and I haven't got a ball, the retaining ring or a cable for it so I've no idea if it works.

I read a post about Acorn mice with failed leds a while ago, I seem to recall that the leds looked discoloured, so that's an obvious indicator that there's a problem with them.

Interesting you commented about screws under the skates - all the Acorn mice I've seen have screws separate to the skates.
I was referring to usb optical mice that I've tried to repair, not Acorn mice.

sP1d3r
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Re: Acorn Type 1 Mouse feet

Post by sP1d3r » Sat May 23, 2020 8:01 am

:oops: I just noticed that the current draw of a type 4 mouse is 125mA. I recall reading the technical reference manual for, I believe, A30x0 & A4000 and the manual states that the maximum current draw for a mouse should be 100mA.
I suppose that it's possible that the A3020 has a beefed-up psu in comparison with an A3000, but it may be the case that using type 4 mice results in a mouse that suffers from faulty leds, after a certain length of time.
philpem wrote:
Fri May 22, 2020 9:04 am


It's probably a Type 4, aka the "RISC PC mouse": http://chrisacorns.computinghistory.org ... Type4.html
About the least repairable variant (in my experience), they suffer from LED failures. You have to cut tracks to fit new LEDs, but that's only if the PCB hasn't failed first. In my experience some track repair (with epoxy) is almost inevitable.
I think that cutting off the old leds on the component side would make removing the legs individually with a soldering iron easier and avoid damaging the pcb. Of course, the legs should be loose in the holes before removal of the whole thing at once is attempted. :idea:

philpem
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Re: Acorn Type 1 Mouse feet

Post by philpem » Sun May 24, 2020 1:06 am

sP1d3r wrote:
Sat May 23, 2020 8:01 am
:oops: I just noticed that the current draw of a type 4 mouse is 125mA. I recall reading the technical reference manual for, I believe, A30x0 & A4000 and the manual states that the maximum current draw for a mouse should be 100mA.
I suppose that it's possible that the A3020 has a beefed-up psu in comparison with an A3000, but it may be the case that using type 4 mice results in a mouse that suffers from faulty leds, after a certain length of time.
Even if that was the issue, it'd just cause the LEDs in the mouse to glow a bit dimmer. In practice those numbers will be based on a worst-case scenario, a fully-loaded machine. If it were true, a faulty Type 4 would work okay on a RISC PC but not on an A3000 -- which isn't the case.

The failure mode on a Type 4 mouse is complete failure of the LEDs, and applies to
sP1d3r wrote:
Sat May 23, 2020 8:01 am
I think that cutting off the old leds on the component side would make removing the legs individually with a soldering iron easier and avoid damaging the pcb. Of course, the legs should be loose in the holes before removal of the whole thing at once is attempted. :idea:
There are several difficulties with them...

1) The Type 4 mouse is made on an exceptionally poor quality circuit board. SRBP phenolic laminate with tracks on one side only. If the mouse has been dropped at any point in its life, the glue holding the tracks on will weaken. The LED ends up flopping around, misaligned. Attempting to adjust the LED alignment by bending is also guaranteed to break the tracks off the board.

2) The existing LEDs have three pins - two are commoned to one end of the LED (cathode possibly), the third pin goes to the anode. The commoned pins are used to make PCB track routing easier and reduce the number of jumper wires.

3) Replacement LEDs mentioned on here (made by Kingbright, sold by Rapid) are two-pin. This means you need to cut tracks and jumper around them. This further weakens the tracks and pads by reducing the area they cover.

I've been using a Pace vacuum desoldering station to do the repairs - and even so, I've lifted tracks. It seems like some of the Type 4 mice are just a bit, well, under-specced in terms of build quality.

sP1d3r
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Re: Acorn Type 1 Mouse feet

Post by sP1d3r » Sun May 24, 2020 6:47 am

:roll: The 100mA figure was overly generous,
I've looked at the A3020 Welcome Guide, which I downloaded from:

http://chrisacorns.computinghistory.org ... A3020.html

and on page V the figure quoted is actually 80mA.

Because the leds in the mouse operate an opto-coupler pick-up system, the effect of overtaxing the mouse power supply could result in loss of function due to insufficient light levels and erratic power delivery, I'd presume.

Your experience of the type 4 pcb's would lead me to try using something like 1.5mm desoldering braid, cheaper types don't compare with bga rework quality braid, e.g. Goot.
I also cleaned up the led & opto-coupler 'lenses' as I noticed that they were dirty and although the PCB is small, it's mostly ground planes which saps heat from the soldering tip.
Also, vintage pcb's aren't renowned for their tolerance of repair and refurbishing.


Because type 3 & 4 mice are indistinguishable unless the underside is compared it could be why the mouse ended up on an A3020, possibly.
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Type 4 (left), Type 3 (right)

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