Markus,

I am curious to learn more about that 3rd board. You said that surface mounted components were replaced? Could you share any before & after pictures? How long were the other 2 speedometers used; was it more than 20-30min? Without knowing more about your car, could there be a problem between the instrument cluster and ground?

*Break*

When I fixed my odometer the other day, I took the car for a test drive. After a few miles, my odometer blanked out. When I got home and shut the car off for a while I then turned it back on. The odometer came back to life. Further testing is still needed. Perhaps Markus' issue with his 3rd speedometer and mine are similar now? Perhaps there could be an issue with grounding the instrument cluster?

Looking at the schematic, the instrument cluster ground is at Ground Point #3. That is located on the engine block. The ground wire leaves the instrument harness at X-17 and enters dash harness. Ground then leaves the dash harness to the engine bay via emissions harness at X-14. The schematic is a bit vague to its physical location. Does anyone have a good photo of the ground wire's physical location? Is it connected to the UIM? Refer to Schematic C-1a, Pg Z-42 of the electrical diagram manual.

Oh, if anyone has an auto trans, Ground #3 travels from connectors X-17 to X-07 and then to X-14.

Cheers,
George

Hi

Sorry I don't have before and after pics as it's done by a friend of a friend . The first and second clusters where tested for more than an hour . As far as I know he replaced all the resistors and diodes on the 3rd one as well as all the caps . The next thing I gonna try is to remove the speedo from the cluster and try it in another cluster . All 3 clusters have knight sport 300 km h speedos . Mileage on the first was 40k 2nd 168k and the third had like 10k on the clock . Hope to get the cluster back in the next few weeks after they tried the speedo in another cluster .

Markus,

Did your friend replace the surface mounted devices on the back side of the board as well? Or did he replace the resistors, capacitors, etc... on the front of the board? Perhaps it was a mixture of both?

I have a running parts list of speedometer components in another thread. Therefore, I'm curious to see what was replaced and to compare part numbers and/or component values. Specifically, what diodes and/or Zener diodes were replaced?

Cheers,
George

Well, at mile 2.1 at least thats when I noticed, my odometer came one. I only put about 20 miles on it but it stayed on the entire time..Woo Hoo for now.

My issues are similar. I replaced all caps and reflowed all points but no change. I even tried de-oxit on all connection points and bent the ribbon connections outward for a more positive connection.

The odometer is bright, crisp and perfect for maybe 5 minutes. Then the digits are gone. It then comes and goes as it pleases. More recently the tach and speedo stop working intermittantly too. The odo is never on when the gauges stop. I have a separate ground wire to chassis to see if that might help. No difference.

Sure seems like a specific component that regulates power needs replacement. Sure would like to know what it is.

​​​​​​​Anyway, I give up. This is my 2nd cluster and 2nd time replacing electronics. I ordered a new speedo and tach from Speedhut. It's become too time consuming to mess with it.

does anyone know which direction the ZD7 diode goes? my diode went bad *i think

Take a look at this link: https://www.rx7club.com/3rd-generati...nents-1112010/, Post #8. The photo shows which direction ZD7 is oriented. What problem are you seeing that makes you suspect that ZD7 failed? Do you have any photos to share?

thank you, I pulled the diode and got a reading both ways... so I'm suspected it's bad but i'm not very well versed in electronics so yah could be wrong

I understand your pain and frustration with the speedometer and odometer. My odo comes and goes as well. I hope that new speedo fixes your problem! Would you please keep us posted on your progress?

I believe that further troubleshooting is necessary of the ground signal going to and from the speedo board. It becomes a big PITA because of the flex board on the backside of the instrument cluster, dealing with the hard connectors, potentially damaging the gauge hood, and tracing signals through multiple wire harnesses.

If the ground checks good then my 2nd plan is to further examine the IC chips on the Speedometer board. I suspect that the display driver IC may need to be resoldered. That proves to be more challenging because the leads on the IC are very small and requires more advanced tools (and skills) than a standard soldering iron from Radio Shack. The potential good news would be the driver IC may not need to be replaced; only resoldered.

Cheers,
George

You're welcome! Do a google search for testing a zener diode. There is a pattern in the resistance readings. Is there any other damage to the board? How do your capacitors look?

I did this fix and it worked great right away. But then, like others, the ODO would be off and then come back on after awhile driving.

I found that if I put my battery charger on and made sure I had very strong voltage, then it would work.

So, it looks like for me (maybe others too) that low voltage is what is messing with the ODO going blank after the fix. It appears voltage just needs to drop a bit and it will go blank.

Others can try charging their battery fully to see if this is the issue. This also makes sense when driving for a period of time because of how the alternator is charging the battery.

Weird question, but the 6.3v one, I couldn't find except I did find a 35v one. Would that still not make it work? Probably just have to find one online, the local store only had 35 and 50v capacitors.

What component are you referring to? The 1,000uF, 6.3V capacitor is found on DigiKey. Unless you have a Radio Shack in your area (they went out of business from my understanding), then DigiKey or Mouser Electronics are the way to go for electrical components such as capacitors, diodes, resistors, and transistors, etc...

The part numbers can be found earlier in this thread or at FD Speedometer-Odometer Circuit Board - Odometer Components.

Cheers,
George

Yea I had picked up one from radioshack but it was a 35v 1000uf. Didn't know if the 6.3v made a difference as it didn't seem to work. Ordered the 6.3v online though.

The capacitor rated at 1000uF & 35V is way out of spec for that part of the circuit. It was wise to order the proper replacement. You may want to examine the rest of the circuit board for anything else unusual. Did you de-solder the speedometer from the circuit board already? Feel free to take some photos and share in this thread. You may not be aware of other potential bad components.

Cheers,
George

I did have to desolder the speedometer to reach some underneath, replaced the ones in this thread that were circled and the larger one seemed to be the only one with some fluid on it. Replaced maybe 3 of the smaller ones as well since I was in there. They are all the exact specs of the ones removed now, but still no good on the odometer. I think I read in here about maybe having to remove the actual display to look underneath as well? The backlight does work on the odometer, just not the digits.

Yes, I said that I may have to remove my display however, that requires a bit more skill and solid nerves to remove. Before you do anything else, re-examine your board.

When you replaced the capacitors, did you observe the polarity of each cap before it was soldered in place?

The electrolytic caps are polarity sensitive meaning they have a positive side (+) and negative side (-). The caps will not function properly if the polarity is reversed. Each electrolytic cap will have a stripe along one side, that indicates the Negative (-) lead and must be soldered to the negative pole on the circuit board. Use my other link for parts identification and location when comparing your board to the photos.

Have you inspected the power transistors for anything unusual? Corrosive deposits, burned up legs, or broken legs?

Since your speedometer is desoldered from the circuit board, take some photos and share with the forum. Make sure you get some close-in shots, please. Collectively, we could help fix it.

Cheers,
George

I first didn't pay any mind as the capacitors didn't have anything that showed until I read about the positive being the longer leg so I redid all of them today with the neg spot on the board. Didn't check anything else but the capacitors or anything that looked burn't. Weird thing was it went out after I raised the engine as high as possible to redo the oil pan gasket and motor mounts. I checked around the transmission as well and didn't see anything out of the ordinary. Will get some pictures when I take it out again next week since there is a show this weekend and I am not too worried about the display for that.

And also when put back together the speedometer sits at 0 but with a bit of car movement it goes a hair below 60 and stays there until I take it apart again. Will do some pictures when I have it apart again.

Here are some shots. So right now the speedometer goes up to around 60 and sticks there, and the digits on the odometer don't work, but the backlight does as well as everything else in the cluster. The 6.3v capacitor was the one that seemed bad before changing them.

Thanks for sharing the photos of your board. I see some potential problems with it.

First, the easy part. Use a cotton swap with alcohol to clean up old flux stains around those brown stains. Specifically, clean up areas around the solder joins labeled "2702", the speedometer area, and the leaked electrolyte around the 1,000uF cap you replaced.

Second, inspect the solder joints below the 1,000uF cap. Look at ZD5, ZD6, ZD7, TR7, and DA1. They should be clean, bright, and shiny.

Third and most importantly, the solder joints on the replacement capacitors need to be replaced. The solder must be completely removed from the eyelet. Then reapply new solder to each eyelet so that it forms a cone shape on the component side. Each solder joint that is replaced should look like the others on the board. Use flux (in liquid or paste form) to aid in flowing the solder thru the eyelet. I believe there is soldering advice given earlier on this thread. Otherwise, YouTube should have some helpful videos. After the joints are flowed properly, use a cotton swab with alcohol to clean any remaining residue. When done properly, the solder joint should be clean, bright, and shiny.

When reinstalling your speedometer, follow the same soldering procedures. Speaking of speedometers, when does it reach 60mph - when you start the car and it idles? Or does it go there when the car is driven at any speed? Was the variable resistor marked "VR" on the circuit board adjusted?

One final thing to inspect: examine the capacitor C1. It looks like the eyelet and run (between the board layers) are charred. Was that eyelet damaged?

I suspect the wacky problems you are experiencing may stem from poor solder connections on the replacement components. Fortunately, this can be easily corrected with a little time, patience, and a steady hand. Again, check some earlier posts in this thread for soldering advice.

Wish you the best of luck on the repair and keep us posted.

On a positive note to this thread, my odometer currently remains on and works properly after posting my speculation in Post #209 (26 Apr 2017). The only thing different between that post and today was a replacement alternator. However, this observation may be coincidental than causal.

I'm just glad that it's working...and yes, I'm knocking on wood!

When starting it goes to maybe 20, and then moving at any speed it goes to the 60 spot and stays there until it's unplugged. Haven't messed with anything but the capacitors so far. Will try again and do a clean job. Thanks for the help.

Does your tach work properly?

Yep, everything else works except the speedometer and odometer. The speed always reads super wonky in my logs on adaptronic ecu.