Jump to content
Sign in to follow this  
sdgmc05

1990 520h tachometer not working....

Recommended Posts

sdgmc05

Picked up a 1990 wheelhorse 520h recently and noticed the tach wasn't working at all. I checked all obvious problems( broken damaged gauge and wires) but everything looks fine.all other gauges are working properly also. Common problem? Easy fix? Thanks in advance.

Share this post


Link to post
Share on other sites
 
Save Old Iron

.

Several possibilities. One is the sensor wire to the gauge has beome disconnected from the rectifier / regulator. The tach gauge "counts" the AC pulses per minute coming off the charging stator and represents them as engine RPM. One of the terminals on the RR unit will have 2 leads, one to the stator and the other to the gauge. A corroded terminal could be the issue.

Another issue is incorrect placement of the terminals on the RR unit. One of the AC terminals on the RR unit is directly connected (internally) to the B+ terminal of the RR. If the tach input is connected to this terminal, the tach willnot function properly. I think I helped someone with this very same issue not so long ago. A search for 520 and tach should reveal the thread.

Third, the gauge could be fried as seen in autopsy pictures below. Usually, removing the illumination bulb from the guage housing and giving the gauge the "sniff test" will reveal the smell of burned electronics.

520HTachometerAutopsy002.jpg

520HTachometerAutopsy003-1.jpg

R8x6tach004.jpg

520tachconnectionslabeledjpg.jpg

Share this post


Link to post
Share on other sites
 
sdgmc05

Thanks for the info, turned out to be corrosion on the connections. I cleaned them up and it works perfect.

Share this post


Link to post
Share on other sites
 
BMW Phil
On 8/2/2012 at 12:06 AM, Save Old Iron said:

Another issue is incorrect placement of the terminals on the RR unit. One of the AC terminals on the RR unit is directly connected (internally) to the B+ terminal of the RR. If the tach input is connected to this terminal, the tach willnot function properly. I think I helped someone with this very same issue not so long ago. A search for 520 and tach should reveal the thread.”

 

I thought this unlikely- I thought that BOTH AC terminals would be isolated from B+.

i just finished replacing the 9-pin connector and the fuse block on my ‘96 520H, due to corrosion, and upon restarting, no tachometer.

i tried swapping the AC leads around, and viola! Tach is back!

On my machine, the grey AC wire with the black tachometer signal wire attached must be connected to the RR terminal towards the back, or it won’t work.

Always learning......

 

On 8/2/2012 at 12:06 AM, Save Old Iron said:

 

 

520HTachometerAutopsy002.jpg

 

 

 

 

520HTachometerAutopsy003-1.jpg

 

 

 

 

R8x6tach004.jpg

 

 

 

 

520tachconnectionslabeledjpg.jpg

 

Share this post


Link to post
Share on other sites
 

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...