i have a 1993 Touring model car that had a non working tach and odometer when I bought it. I had a local electronics shop replace all of the capacitors in the cluster, and resolder the leads on the back of the tach. After that, only the odometer didn't work (backlight comes on, but no numbers appear). I searched on here and did the recommended fix where I added an extra power and ground to the two points on the back of the cluster. There was still no change. That was roughly four months ago.

Today, my tach and speedo are not working at all. The odometer backlight still comes on, and the rest of the gauges work. The CEL also popped on. I pulled my cluster and verified that I am still getting 12v in and out, and everything on the circuit boards looks fine. I am starting to lean toward the speedometer sensor in the transmission being the culprit, but I can't find any info on how to test it or where to even buy a new one (Mazdatrix only offers it for automatic trans). Any help is appreciated, as my searching is turning up nothing that I haven't already tried.

*Edit* I jumped the diagnostic port and I am getting two codes:
06-speedometer sensor no signal
40-purge control valve open/short circuit

 

Double check your connectors on the back side of your instrument cluster. Slightly bend out the flex print and then reinsert the connectors. Sometimes the flex print will not fully engage the hard plastic connectors.

While the cluster is removed, take another look at the speedometer board. Use a magnifying lens and a light to see the board at different angles. Check again for anything unusual, swollen capacitors, etc.

Wish you the best of luck!

 

the speedo sensor just generates an AC voltage, so you can put a volt meter on the wires and spin it.

 

I inspected the board and couldn't see anything that looked problematic. I already verified that the terminals I added were making good contact with the screws on the back of the cluster, and that there is definitely 12v at each of those terminals.

Is is it possible that the speedometer itself has gone bad? That could explain why the tach died at the same time. I did not resistance test the speedometer to check for an open circuit.

 

It is possible that the speedometer itself is bad, however the likelihood of its failure is low. If it did fail, the speedometer would be the only gauge that wouldn't work. After looking at my speedometer circuit board, IC6 drives the speedometer.

Desolder the speedometer and inspect all of the components. Perhaps a capacitor leaked after repairs were made? If you suspect a solder joint to be bad then remove the old solder then reapply new solder to the joint. It is important to never reflow old solder because the joint's electrical properties were already compromised. Additionally, it is important to verify the solder work of the company that repaired the board. Just because a business offered a service doesn't necessarily mean that the job was done right.

 

I pulled the cluster apart today. Nothing but bad news. The heat sink(?) looks to have caught fire and torched the board around it. There's no hope of saving the board. The pics are hard to see because I couldn't get my phone to focus, but you get the idea.

 

Holy crap! I'm sorry to see that catastrophic failure of your speedometer circuit board. Did you smell anything burning? It wouldn't hurt to check your fuses too. Specifically, the METER fuse, I believe it's a 10A fuse.

In my opinion, I don't like the https://www.rx7club.com/interior-ext...epair-1055763/. There is too great of a chance to have wires short out. That may not be the case with your board but one thing for certain is that your board absorbed a lot of heat! It would be interesting to find the cause of this damage.

There may be a chance to salvage your circuit board. It depends on how much damage was done to the solder runs within the circuit board. Another thread here https://www.rx7club.com/3rd-generati...these-1109714/ suggests a company in TX called Zepco. Do your best to take better pictures of the board. Should you decide to contact Zepco, you could email them photos of your circuit card and they could assess the level of repair. Could you also tell if ZD6 (that big monster of a diode) is damaged?

Additionally, I started a thread here: https://www.rx7club.com/3rd-generati...nents-1112010/. This thread lists all the components and their respective part numbers. It is a work-in-progress though.

For now, you may want to check the wanted & for sale forums for an inoperative speedometer circuit board. You can still keep your car's mileage by swapping out 1 IC chip. You may be able to repair that one and install the mileage chip. Refer to this thread when repairing a speedometer circuit board: https://www.rx7club.com/3rd-generati...ometer-599220/

Again, I'm sorry to see your board go up in smoke. It's a good thing that you checked it before chasing other gremlins.

Cheers,
George

P.S. You may want to still de-solder the speedometer from the circuit board. It may not be damage and could be salvaged. By removing the speedometer, it also gives you better access to the fried board and allows you to take better pictures of it.

 

I didn't smell anything until I took the cluster apart earlier this evening. I had already checked all of my fuses, they were all clean and in good shape. I'm hoping to find another cluster that I can swap the speedo out of. My odometer hasn't worked since 2007, but I would swap the chips just to see if anything transfers over.

 

So the big question is when did your circuit board go up in smoke?

If your odo hasn't worked since 2007 then there is a high possibility that it hasn't recorded any mileage since. That is a double-edged sword because your car's mileage will be much lower over the 10yrs you owned it. If the odometer isn't working then some states/localities may consider the car as tampered because the mileage is fraudulent.

In my instance, when my odometer blanked out the system didn't record any mileage. Just giving you some food for thought.

 

The title shows "inaccurate odometer reading". I bought the car with an inoperable odometer. I had all of the capacitors replaced in an attempt to repair the odometer, but it still didn't work.

I drove the car last Sunday, 3/12, and everything was fine (minus odometer). I started the car on Saturday, 3/18, and I had no tach or speedo. Either it burned up one day while it was sitting, or it happened on Saturday after I started it to let it warm up while I was inside my house.

Also, I have only owned the car since July of 2016. I bought it from the original owner, whom I know personally, and he included receipts documenting the car's entire maintenance history since new.

 

That's some good documented history on the car! It would be interesting to see what the mileage shows when the odometer display is fixed.

I am still amazed at the level of damage in the cluster. You are very lucky that the car didn't catch fire! Have you started the hunt for a new speedometer circuit board?

Cheers,
George

 

Red,

Since you posted this photo, is that black tape on the backside of the board? Or is that a 10uF capacitor soldered there? If so, I doubt that it was soldered there from the factory.

Cheers,
George

 

Yes, it is black tape and a capacitor. The electronics shop put it on that side of the board when I had them attempt to repair my odometer.

I will be buying a new speedometer from mazdatrix, unless I stumble upon someone selling one used for much cheaper first.

 

I thought I would post an update. I purchased a brand new speedometer assembly from mazdatrix. I started installing it today, and before I set it into place, I noticed some discoloration on the green flexible circuit board on the back side of the cluster where it plugs into the speedo (similar to a ribbon cable). It also felt brittle. I folded it over, and sure enough, it was burnt where two of the conductive strips had touched each other and shorted out. I didn't get any pics, but I am now in search of another cluster (again). I'll be installing the brand new speedometer in whatever cluster I end up buying.

 

Red,

Thank you for the update. Will you swap out odometer chips? Are you saying that your instrument cluster is damaged? I am sorry to hear about it. Is it still possible to take photos and share with the forum?

Cheers,
George

 

I plan on swapping odometer chips after I verify that the odometer does work. I'll get pictures of the fried area tomorrow.

 

 

Red,

Ouch! Man, I'm sorry to hear and see the after effect of burned up flex print. Are you searching the forum for sale section for a new flex board? Could Ray Crowe help in your search?

If I may also make a recommendation - do not add the extra power and ground wires to the back of the flex print board when the replacement arrives. After re-reading your posts, I would bet dimes to donuts that may have caused the over-voltage on your board.

Since you found this burned up segment, it might be a good idea to remove the other gauges and inspect them (and the rest of the flex board) for damage. Perhaps the wiring schematic could also show other areas to inspect for damage.

PM me if you need a hand in troubleshooting the circuit board. Best of luck to your search for a new cluster circuit board!

Cheers,
George

 

I purchased a cluster off of eBay. Working condition is unknown, but the flex print looks good in the pictures. I will be installing my new speedometer into this "new" cluster, and touching up the solder joints on the back of the tach. I'm hoping there won't be any issues after that. And thank you for the offer, George. I'll be sure to message you if I need any help.

 

Red,

I wanted to follow up with you on this older thread. How did the repairs go on your cluster?

Cheers,
George