Jan-Erik Soderholm wrote:
> My question is, would it generaly be possible to use 1% values, if
> they "fit" within the +/- 5% "range" of the BOM values ?

Sure.  That would make them indistinguishable from 5% resistors.  In fact,
you should be able to do better with 1% resistor going back to the schematic
to figure out what the best ratio really is, not the compromise made to hit
5% resistor values.

Most resistor values can tolerate a lot more than 5% error, but a few are
used in voltage dividers that need to be a specific ratio.

For example, R8/R11 and R9/R12 are voltage dividers that ideally divide 13V
down to 5V.  Any error here effects the 13V Vpp voltage.  The values shown
on the schematic are a compromise to what is available in 5% resistors.  You
should be able to do better with 1% resistors, keeping close to the same
overall impedence.

Other dividers are R19/R21 and R20/R22.  Both these ideally divide 6V down
to 5V.  The accuracy of these dividers effect the Vdd voltage values.
R29/R31 is also a divider, but not very critical.  Ideally it divides 5V to
3V.  It's job is to make 1/2 of the target chip Vdd to compare the returned
PGD signal against during readback.  A 5V level on the VDD-PWM line causes a
6V Vdd level, which is why 3V is desired out of the divider with 5V in.
This divider is good enough as long as its output is roughly half of the
target chip Vdd.  You can easily substitute any near value to the ones shown
in the schematic.


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