[GreenKeys] Model 33 Q1 transistor replacement

[Erik Bruchez]

Another update:

1. I unexpectedly acquired a Model 33 RO yesterday, and it has a good SMD
board as far as I can tell.

[image: image.png]

2. On my bad SMD board, I tried replacing the transistor with a fairly
regular PNP transistor. I had, it turns out, a leftover MPSA56, which is a
PNP transistor that happens to support slightly higher voltage and current,
while being in a small TO-92 plastic package. This is probably overkill,
but that's what I had. I soldered it in, and the selection magnet appears
to work! I don't want to prematurely recommend this transistor in
particular over another, but I suspect that this board is not very
sensitive to the model of transistor used.

[image: image.png]

-Erik

On Tue, Jul 29, 2025 at 6:26 PM Erik Bruchez <erik at bruchez.org> wrote:

> Terrific photography!  And an amazing project.  That TTY cleaned up really
>> nicely.
>>
>> Well done!
>>
>
> Thank you, Paul! There is still a lot of work to be done :)
>
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