On 3 Oct 2011, at 16:22, Thomas Harte wrote:
> It looks like a previous owner of my current SAM has had occasion to
> replace resistor R55, or at least, to solder an additional copy of R55
> on top of the existing one. See http://postimage.org/image/1g4kbz490/
>
> Immediate follow-on questions, mostly resulting from me being an
> electrical dunce, are: what does R55 do, what would be the likely
> effect if it was a bit dodgy and is it really okay just to solder an
> extra resistor on top of an existing one?
According to the schematics in the tech manual, R55 is doing something to do
with the MIC tape interface, and should be a 100kΩ resistor - which if I'm
reading the photo correctly (the colour bands look {brown, black, yellow,
gold}) is exactly what it is.
Two of them wired in parallel are equivalent to a single resistor of 50kΩ
(assuming they both work) though I'm not certain what the implication of that
is for the rest of the circuit.
(R61 to R75 look like they are something to do with video generation).
Andrew
