Sewer backs up, and speedo smokes.
 

Just one of those effing days.

Sewer backs up.

Call rotorooter.

To access clean out, must move cars out of garage.

Start up Porsche... Wait a minute to let warm up. Back out into alley, ands smoke starts poring out the miles reset hole on the speedometer. That awful acrid electrical fire type smell.

Fcuk. Why? Why? Why?

Here's a couple of pretty photo's so you can enjoy my misery.

Not sure yet WHY the resistor decided to smoke...

VDO Sucks. [I can't say that with enough emphasis.] I think I have only owned ONE 911 that didn't have a speedo failure.

http://forums.pelicanparts.com/uploa...1192549922.jpg
http://forums.pelicanparts.com/uploa...1192549959.jpg

Can you simply pop a new resistor in from Radio Shack?

I don't know, it could be worse. It could be Lucas.:eek:

Good luck with everything. Sewer troubles are a real nightmare. Ask me how I know.

Err, actually, don't. ;)

To fix sewer problems, cut down every tree within 100 feet.

To fix VDO speedos, I'm not sure I'd trust that one. Why is the question indeed.

+1

Roots can and WILL find sewer lines 10 times out of 10.

So, here's the autopsy, and the back to life repair:

The resister that burned up was a 33 ohm resitor. It was in series with the +12V, so all power for the speedo goes through it.

I ohmed out the circuit, and it was showing about 0.2 ohms... Hmm, must be a short somewhere. If I'm unlucky it would be the IC...

Turns out it's the 16V 47uF cap. What fcuking VDO moron [engineer] decided to put a 16Volt cap in an automotive circuit? Any electrical design engineer that got a D or better KNOWS that you de-rate caps by at least 1/3 in a circuit... So 16 Volts times 0.66 = 11 volts. So we have an 11 volts cap in an automotive circuit that's gonna see above 15 volts lots of the time.. Gee, no wonder those caps die ALL THE TIME.

Like I said, VDO Sucks (At least the speedo designed by VDO for Porsche SUCKS anyway.)

Replaced the cap with a 35 volt one. Replaced the burned out 33 ohm resistor, and wow. It works! Old 16V 47uF cap and burned out resister shown at left of picture.. New parts are installed.
http://forums.pelicanparts.com/uploa...1192558594.jpg

I'd rid the board of the other cap, as well. Is that one rated at 16 VDC, also?

Yes,..fresh dielectricS!

Best,

Amen to what Doyle said!

Deja vu, huh? I think we already knew your opinion of VDO ... from your adventure two years ago!

http://forums.pelicanparts.com/porsche-911-technical-forum/247776-carrera-vdo-speedo-sucks.html

I guess I am surprised you don't have ziploc bags with 47 uF & 100 uF at 50 V, and 33 Ohm resistor 'kits' stapled to a bulletin board, marked: '3.2 Carrera speedo CPR kit'!!!

Warren,

That's funny as hell....a VDO "kit".....terribly overpriced, of course.

Best,

Warren,

That's funny as hell....a VDO "kit".....terribly overpriced, of course.

Best,

Certainly to include the most expensive, esoteric electrolytics (ESR's of ZERO!), coupled with Dale 1% tolerance, low noise, metal film resistors......comfortably power-overrated. The advanced package would contain a few extra goodies for added protection, such as better RFI suppression and (of course, onboard voltage regulation....

...and don't forget the chip upgrade (mega$)...


.......just joking, guys. Although, if I were to engage this failure, I could pull some high end components from my electronics stock,..compiled from MANY years living, designing, modifying tube amps.........hell,..now you've got me in the "preventive" mode.....just as I used to recap many old weak power supplies in guitar amps, maybe I need to embark on a capacitor rebuild project on the P-car. ..yes,..to change EVERY SINGLE electrolytic in the car (yes, including the DME filter caps).................................here we go.

best to all,



Best