Speedometer with Microsquirt?

[whalenlg]

Schematic shows 680, so I’d go with that.

[Tom]

Schematic shows 680, so I’d go with that.

You have a schematic for that board? Is it in the factory manual? If not, any interest in posting it? My bench cluster is the 180mph version, which has 2 (more complex) boards.

[Drscottsmith]

This one I posted is a 180 as well.

Two boards arranged in an ‘L’ shape but not actually connected to the Speedo and then the one I posted that is attached to the Speedo.

[Tom]

This one I posted is a 180 as well.

Two boards arranged in an ‘L’ shape but not actually connected to the Speedo and then the one I posted that is attached to the Speedo.

Ah, let me check again...

[Tom]

So the bigger half watt resistor seems to be 33 ohms based on the stripes (orange orange black gold). It measures 32ohms in situ, so that's seems to corroborate -- though you never know if the rest of the circuit is affecting the measurement. The 1/4 watt one seems to be a higher precision 130ohm based on the stripes (brown, orange, brown, red) -- and that's also about what it measures in situ.

IMG_5971.jpeg (1.85 MiB) Viewed 165 times

[whalenlg]

The schematic is in the referenced post from earlier in the thread. That was from the original datasheet for the ic.

33 could be right - I’ll have to dig into my data a bit deeper as I’ve been out of town the last few days.

[Drscottsmith]

It looks like the second cap is actually 100 ohms and not 16 like I thought…. Thanks for that pic. The second zero was not clear on my board.

Yep I know from pinball work that measuring in situ is not a good thing (with pinball it seems to be more of a thing with diodes), but at least it provides a sense of direction and a starting point.

I will report back.

Thanks
-scott

[whalenlg]

Sorry for any confusion - it is indeed 33 ohms (found an Amazon receipt)
Adding the full datasheet that specs 33 ohms in the recommended operating conditions table and a schematic from a similar era 911...

[Tom]

Very happy to have that schematic, thanks Mike.

The stripe colors on mine were pretty clear, and matched my multimeter, so the odds were pretty good for 33 and 130. Be mindful that the 33 is 1/2 watt, and that the 130 is a 1/4 watt but with a 2% tolerance --in other words, neither are the typical 1/4 watt Radio Shack (yes, I'm that old) resistor... Still easy to find, just need to be mindful of the specs.

[Drscottsmith]

Got it - thanks all!

Working Speedo is nice to have for sure.

Will post more details and pics.

Thanks again!!

-scott