Pauly951

Hi all,

I'm in the midst of refurbishing my '87 951 speedometer and I've hit a snag. A resistor on the VDO board is toasted... it took out a wire to the DC motor driving the odometer and potentially (what appears to be) a capacitor next to it. I haven't had much luck determining the pre-cooked value of the resistor. Anyone have a spare gage laying around they can take a shot of so I can read the resistor color code?



Picture of the crispy resistor:
https://picasaweb.google.com/lh/phot...eat=directlink

KuHL 951

I have an 86 NA cluster on the shelf if you think the resistor is the same but I doubt it. If it's the same I can check for you as long as I don't have to split the case to get to it.

Pauly951

Based on discussion I've read pertaining to the NA vs Turbo gages I wouldn't know if they have the same resistor... you definately need to split the case of the cluster to get the picture. This board rides on some foam bushings supported by the posts of the speedometer.

Thanks though.

JohnKoaWood

Just happens I have one sitting on my desk right next to my computer! Out of my 87 Turbo!

Pauly951

Thanks!!

Pauly951

Well, I successfully repaired the speedometer to whatever condition it was in prior to the resistor going up in smoke. Unfortunately, I reached this conclusion because it immediately went up in smoke again.

A little history... The odometer gear was crumbled and had locked up the gear train driven by the small DC motor integral to the gage when I obtained the car. Assuming this was the problem, I replaced the gear. No dice. Upon further inspection of the gage, I noticed the burned out resistor; however, not before replacing the sending unit on the tranny.

Back to this evening... I replaced the resistor, verified no paths on the back of the board were bridged, and then reassembled my speedometer. Installed the speedo into the cluster and hooked up all the wiring harnesses. At that point I connected the battery and fired her up. I put the car in gear (on stands) and no speed. I spun it up to about 1500 RPM to be sure it wasn't just too slow.

About 20 - 30 seconds had passed since I started the vehicle. This is when I noticed the thin stream of white smoke coming from behind the cluster and the smell of burning electronics. I immediately shut down the vehicle, disconnected the battery and pulled out the cluster. I didn't need to check, but I did... resistor is toast again. The odometer dc motor was still warm by the time I got to it.

For some reason, too much current is flowing through that resistor. Any ideas where to look for problems?

Also, while I'm thinking of it, can the speedometer and odometer operate independently of one another (ie if one is malfunctioning will the other function normally)? Everything goes back to the board, but the circuits might still be independent. In which case I could be looking for multiple issues.

Thanks in advance...

PS. At this point I'd hate to put another gage in that cluster, risking yet another cooking lesson.

JohnKoaWood

Motor is shorted.

Measure it with an Ohmmeter, I bet it is internally shorted.