And Another ATTABOY. Wilton
----- Original Message ----- From: "Jim Cathey" <jim.cathey...@gmail.com>
To: <mercedes@okiebenz.com> Sent: Sunday, March 29, 2015 7:38 PM Subject: Re: [MBZ] SL
I had time to take off the steering wheel yesterday, so that I could liberate the dash cluster in order to address the non-functioning tachometer. The center Allen bolt was _very_ hard to get out, as per usual. I used the new POS Harbor Freight impact driver to loosen it. I think. After much hammering with that I was finally able to break it loose with the big socket wrench, which had not worked by itself. With the dash pod out I was able to test the signal feed to the tachometer, and it seemed fine. I checked the (vulnerable) ground in the cluster, and it was intact. So I took apart the tachometer. Removing the needle with two spoons used as levers agains the face seemed to mess up the d'Arsonval meter movement, it no longer moved smoothly and wouldn't return to zero on its own. I took it apart, even removing the damping-fluid filled plastic needle bearing sockets, and put it back together again, hopefully without destroying it. It seemed to move properly again, at any rate. I was mostly out of time at this point, but when I tried hooking it up on the bench I was able to get a small intermittent wiggle/buzz out of the meter, so I know the movement is intact. With more time today I tried to hook up the tachometer on the bench. I wasn't really getting anywhere, so I retrieved a spare tachometer from the parts pile and tried it. Nothing. So I took it to the car and it worked fine there, though it did read high. (It might have been from a 6-cylinder.) I then brought it back in and figured out that there are _three_ connections: power, ground, and tach signal. It's not powered through the tach signal, unlike some systems. Once I figured that out I could get the spare tach to react to the signal generator as I'd expect. I moved back to the DUT, this time knowing I had it hooked up correctly. Probing around the fairly simple circuit board showed that the circuit was all apparently floating up at Vcc. When I poked the resistor to ground with my finger I burned myself, which told me what was wrong. I pulled the wretched Frako 47uF 16V electrolytic filter capacitor and found it shorted. (Those things have a _horrible_ track record in my experience.) I replaced it with a new one, and after that the tach worked on the bench, and in the car. I put the cluster back together and set it back in the car. While I've got the dash cluster out I want to check all the lighting, but I really need to wait for dark to do that. -- Jim _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
_______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
