'79 Speedo not working

[Rupesy]

So I decided to fabricate a bracket just so I had some peace of mind when I got this all back together. I found an old plastic bracket from a wire mesh closet shelf. I measured, cut and sanded it down to size. I used the soldering iron to melt the plastic to hold the flex board in place in a couple places. Screwed in place with some short screws that don't go all the way through.

[Rupesy]

Once I got the bracket going, found another issue. Two had obvious breaks and then I found one on the left side at the top. The one on the left was a lucky catch since it was part of the speedo sensor circuit. Was still intermittent after all the other soldering. Just a hairline break was enough to cause issues. Well, I have not tested this yet in the car, but I know I am definitely closer to a solution.

[Rupesy]

SUCCESS!!!!!

Since the weather has finally gone above freezing, I decided to take a stab at seeing if anything I did worked. I have the car on jack stands so I plugged everything in, started the car, put it in 3rd gear and hit the gas and found the items that I intended to fix worked!!! The original items were the turn signal light, speedometer, and odometer. The turn signal works, the odometer works and the speedometer also working. I will attribute the issue to two different things. The turn signal seemed to be the broken circuit at the main connector that I soldered. The speedometer seemed to be mainly because of the poor connection of the rivets from the flex board to the hard circuit board behind the speedo. The lost signal to the speedometer seemed to be a fine break in the flex board at the main connector. The odometer is in good shape, just was not getting power and signal. The fine breaks at the main connector definitely due to the rig job by the PO. Included a picture showing the speedo at about 20 mph and a few tenths on the odometer.

[JhwShark]

Well Done!

[P928s2]

Hi, nice job.

While you were repairing your speedometer, you mentioned someone had already been in there to replace the motor and a resistor. Did you happen to take a picture of the circuit board of the speedometer? I'm checking mine now and found a burned resistor. I want to replace it but can not identify it's value. If anyone has got that info, I'd be superhappy.

Grtz

Stefan

[MPDano]

Great job. Exact;y what I did last year on the Euro. I also put reflective tape on the Refractors since the backlight was so dim. Here's the thread:

Porsche 928 Forums dot com - View topic - Pics of my First 928 and Current Project

[Rupesy]

MPDano, actually I think I got the idea for the bracket from you.....I stumbled across that web page when I was looking for ideas....

P928S2, unfortunately the best picture I have is the lousy blurry picture I took that is in the post on page 2. I don't have any other angles. Normally I take a lot of shots, however, it was extra cold in the garage this winter and I did not spare any time for extra photos LOL!

[Maleficio]

Nice work.

[garylewa]

Originally Posted by P928s2

Hi, nice job.

While you were repairing your speedometer, you mentioned someone had already been in there to replace the motor and a resistor. Did you happen to take a picture of the circuit board of the speedometer? I'm checking mine now and found a burned resistor. I want to replace it but can not identify it's value. If anyone has got that info, I'd be superhappy.

Grtz

Stefan

Hey Stefan,

I have an extra speedo in my garage; I will take of a pic of the board and post both the pic and the resistor info for you on Friday evening.

-Gary

[MPDano]

Excellent!

[garylewa]

Speedo board pics; let me know if you need photos of anything else.

Whole circuit board (for reference)


Top Half


Middle


Bottom half

[P928s2]

Hi Gary,

Thanks a lot for your efforts. If my speedometer was the same, this would have helped beautifully. Unfortunately it is not. Apparently the chipset changed and so did the diagram.
As you can see in the picture, components changed location and I've looked up the chip data. They do the same thing but have got different connections. So my search continues.

[garylewa]

See the green resistor on the left of your picture? I would use that code for the burned out resistor. They look to be in line with the female pin attachments.

[P928s2]

I've found a new one and it's on its way. When it arrives I'll take some pictures and post them as a reference for all.

Thanks for your input, Gary.

Grtz

Stefan

[garylewa]

Thanks, I'm curious if your blown resistor is different from the green one on your board.

[Rupesy]

I'm providing an update to my original post. I got about 200 miles on my odometer before it quit. In hindsight, maybe I should have replaced that gear while I was in there. No telling what it is yet, but figure that might be it. I will just follow up with fixing that over next winter. My speedometer is still working, however, it sticks at 0mph. If I gently tap the clear plastic on the pod or hit a light bump, it pops up into position and works fine until I come to a stop. What causes this? I would like to make a note of it for when I go back in to fix the odometer.

[P928s2]

Still needed to return to this spot to give last info. My new speedo arrived, but, .... its a MPH with exactly the same print as Gary pictured. So I still have no idea how to repair my old one.
Anyway, the new one's in place. And working fine, just need to take care not driving 70 Mph in a 70 km/h zone. It's hard to tell in this machine.

BR

Stefan