looking for some help....
I have a 92 originally 1.6 n/a and it now has a 1.9 aaz in it with mk3 alt / serp set up
the rpm gauge is inaccurate now
i did a search and came up with this
http://www.vwdiesel.net/forum/index.php?topic=12589.0 however i took apart my cluster and it isn't looking like that, here are some pictures of mine


thats the back of my rpm tach........ any incite would be appreciated
I'm not familair with the board, but it appears to be the normal SAK215 chip so - I'd say.....vertical pot looks like 'R3' - make a mental note of it's position and then twiddle it to bring the unit into calibration. If the twiddle yields no response, return to it's original position.
someone must know
Not necessarily... the circuit boards are highly proprietary, no schematics or service info are available, no repair parts are available, and there's many many different flavors depending on model, year, and country of origin. Other than that, easy peasy.

I mention this because a post like "someone must know" has a flavour of "you guys know and you're just too lazy to share"...perhaps not your specific intent... but in general folks here are *extreme* sharers!!
for instance,
vincent here "shared" me his syphilis!
totally extreme! :p