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240 Tachometer fix update

H

hessam69

Well-known member
Joined
Jun 19, 2009
Location
Sydney, Australia
Hi,

Is there any way to bring the 1990 240 tachometer into the 21st centuty ie, less jumpy and bouncy? It is much more solid and accurate in my 940.

Thank you
 
Maybe some solder for the tach board is cracked? My tach would sometimes go out and would come back with a good smack. I bought a cheap $15 soldering iron kit, some solder, and reapplied solder to every joint on the board. It's been working flawlessly since then.
 
Sorry, the tach works, but what I meant was it isn't very accurate (for example when shifting, it moves a lot and isn't steady like say an autometer tach).

Basically big changes in the rpm make it move a lot. With my 940, it's a lot more stable and accurate.
 
It still sounds like an electrical problem. I watched a few videos of the 240 tach in action and it looks like it "should" move smoothly. Check the surrounding ground connections first.
 
Check out that mentioned thread from volvowagon. It is on the first page. Take a look at the brown cap he replaced. Replacing those may help. Also cracked solder joints happen. Use a strong magnifier to look the circuit board over.
 
hessam69, Volvowagoon got his tach to stop jumping after he reflowed all of the solder on the PCB yesterday. I'd almost be willing to bet that's what your problem is.
 
I feel like I should chime in, but everything has pretty much already been said. Reflow the joints and install a new new cap. My signal got super crisp after that. I would have written an article last night if it didn't take over an hour to reinstall Office on my laptop. lol
 
Sounds like the dampening. Analog gauges like fuel and temp all have some form of dampening and it may be electronic or mechanical. Unfortunately, there's no way for us to know which components or solder joints are performing that function.
 
hessam69 said:
Sorry, the tach works, but what I meant was it isn't very accurate (for example when shifting, it moves a lot and isn't steady like say an autometer tach).

Basically big changes in the rpm make it move a lot. With my 940, it's a lot more stable and accurate.
Click to expand...

This happens because the tach moves based on an analog signal and a clock spring. The autometer tach uses a small processor to interpret tach signals and output a degree of rotation position using a stepper motor.

The gauge is working as normal
 
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