Hi folks,

My speedometer and odometer stopped working today.

I had this issue years ago, and I remember I reflowed all the soldering on the PCB foil, which fixed the problem.

Today, before doing anything, I removed the speedometer, and much to my pleasant surprise, it looks new. Also, the PCB is not the same as the one you see in any documentation in NA; it is for EU and from 1996, so I'd say it looks simpler.

See some images below:

https://postimg.cc/3dT3N6Wq

https://postimg.cc/rKNMrJrw

https://postimg.cc/xXjYyzvy

https://postimg.cc/sMnzngKF

Now, I know the issue is coming from the instrument panel because tapping on it makes the whole thing start working again, and I'm certain it's due to a bad solder on the PCB foil.

The only area where I see the soldering is brownish is in this photo I took when I removed the speedometer:

https://postimg.cc/B8X0Rfwj

I couldn't find any weak solder joints all over the foil, but I would like to reflow only the ones related to the speedometer/odometer.

I can't find the schematic of the instrument panel; I mean, I can find one, but it's only related to the wiring, not the actual PCB.

Do you happen to know if those resistors are somehow related to the speedometer/odometer?

If that's the case, I will just reflow them.
If not, are there any other solder joints you would recommend reflowing?

I've attached this image I took in 2015, the first time I reflowed all of them.

https://postimg.cc/QFRDLyLS

NOTE: Weird that the Volvo # on the speedometer does not exist anywhere, I got a different one, although very similar, on VIDA for my car.

Thank you!
Alex

Hi Alex,

That last photo with the diodes and resistors looks very ugly with the
start of some crispy crittering.

Do you get get P0500 or P0535 DTC codes?

If the last digit of your ODO is red, then it is a replacement Speedo.

From my adventure with a 1993 fuel gauge I suggest that you focus on the
flex card tracks from:
Speedo head "S-" to connector A14 pins 3 and 4
Pin 4 is ref ground 31/67
Pin 3 has a unknown series component and just noted as "-" in the info

Speedo head "S+" to connector A14 pin 5
Pin 5 is to 7/33 speedo pickup

Connector A14 is at the top left as you look at the back of the instrument cluster. Pin 4 Black wire Pin 5 Green/White wire

Check especially for tracks that use a through hole and continue on the back side of the flex card and come back via another through hole connection.
In the 1993 flex card there is a dotted line to help you know where to tack a jumper. There's no way you can re-flow the through hole joint from one side
with that flex card.

That joint was haunted since it would work and quit on a timetable only known to famous prankster "Murphy".
In addition I found a loose connection at the fuel sensor connector

I used a little smear of dielectric silicone on the instrument cluster connectors, but wonder if a light smear of Penetrox-A would be better?

Take photos of those tracks from Speedo to A14

Good luck, Bill

Thank you Bill,

You mentioned about the resistors/diodes.

Could their solder joints be the cause of the problem I am experiencing?

Do you think those resistors/diodes need to be replaced?

I found the schematics you refer to and do my best to work from there.

I will keep the community posted.

Thank you,
Alex

Hi Alex,

That photo was from years ago when you resoldered.
Maybe they look better now after you re-soldered.

Check for OBD codes.
Inspect the tracks from Speedo S- and S+ to Connector A14
if the tracks jump to the back side of the flex card and up again, there
is a spot for a short jumper wire. Finding my bad connection took many times
and some luck to be checking voltages when it quit to nail the intermittent
culprit. Attempts to reflow the through hole connection from the top were
not successful. You don't have the same odds with soldering the flex card that you have with a glass epoxy PCB.

Take some pictures of those tracks and share.

Bill

Hi Bill,

I inspected the lines and solder joints again, but found nothing evident. I checked for continuity and everything appeared to be working. So, I decided to reflow the solder joints between S+ and A5, and then between S- and A3, including those of the resistor.

It is now working well, but only time will tell if I addressed the right issue.

Another thing I noticed is that previously there was a 7 km/h difference between the speedometer reading and the actual speed:

Foe example:
When the speedometer indicated 70, the GPS was showing 63 km/h.

After the reflow of today, the difference is now 5 km/h; 70 on the speedometer means 65 km/h.

I'm not sure which component is affecting the precision of the reading, especially after confirming that all the capacitors are good.

I would like to fix this and make it more precise, but I gave up a long time ago because I wouldn't know where to look.

Thank you for your help with this one too!

Alex

Hi Bill,

I have no way to check the OBD codes, I do have an OBDII port on my car, but VIDA will not work on that, I think Volvo at the time used Video 2000 to read those codes.

I never invested in something that is capable to read the codes in my car.

I am sure there is something on the market today, but never really needed it.

Thank you,
Alex

Errata: I meant VCT2000, I guess there were too many similar standards at the time :)