Tachometer problem

[KristersKK]

Hello, I've run into a tachometer and econometer problem. One day the tachometer stopped working as well as the econometer and I thought that the SI batteries might be the cause. So I removed the cluster and noticed that there's no batteries into the SI board and the previous owner had already done some modifications to it by soldering a small wire from one connection to another. But when i was inspecting the SI board I accidentally ripped the soldered wire from the connection, because it was a very small and fragile connection.
But even without that wire the tachometer sometimes comes back to life, sometimes it shows an incorrect reading, sometimes the econometer comes back to life, but doesn't work as it's supposed to. The temperature gauge also does some weird stuff by jumping up and down all the time.
I've tried to search for this problem in many forums similar to this, but it doesn't seem like anyone's had it.
Oh, and the the green and red inspection lights doesn't light up too.
As far as i know the tachometer cant even work without the SI batteries, so how could mine work?? And what do I have to do tofix it?
Should I try to solder the batteries into the place?
I've also tested the signal from the blue plug's 7th pin(i read that that's for the tachometer) and it's showing a normal signal.
Idk, I'm clueless

[Brianmoooore]

Tacho doesn't rely on the SI board batteries in any way, but the charging current for the batteries comes from the same power supply as for the tacho and temp. gauge, so when the batteries go short circuit they overload the power supply and affect the gauges as well.
There's a lot of active corrosion on that board, so there's a good chance that one or more of the copper tracks has been eaten through.
Looks like whoever removed the batteries couldn't be bothered to clean the board.
If you can find the open circuit track(s) they can be bypassed by thin insulated wire, but best of luck on a board with densely packed tracks such as this.

[KristersKK]

Ok, thank you! I'll try to, but if i couldn't be able to do anything, looks like it will be easier to get a working cluster from another car, because the prices for a new SI board are cosmic.

[Speedtouch]

I would have a go at cleaning off all the verdigris (probably caused by the batteries leaking), then re-do any corroded/dry-looking solder joints.

You may possibly have to change some of the diodes/resistors/wire links adjacent to the battery terminals.

[KristersKK]

Just got a replacement Si board from a different cluster, now everything works as it should

[Speedtouch]

Good to hear that, dude. What will you do with the old one, bin it?

[KristersKK]

No, why should i? The cluster i got the board from was an English version with mph instead of kmh and mpg, not l/100km. Well it was in pretty bad condition, it had some underground modifications done to it, for example red painted needles with nail polish, brazzers sticker on it, but overall it's a working cluster just without the SI board. If anyone ever needs some parts hmu

[Cloggy Saint]

How much for the Brazzers sticker?

[Vincethedog]

I haven’t looked into this yet, and I don’t know the first thing to try but my myelomata stop the clocking up the miles any ideas? Thanks in advance

[Brianmoooore]

I haven’t looked into this yet, and I don’t know the first thing to try but my myelomata stop the clocking up the miles any ideas? Thanks in advance

Assuming the speedo. is working as it should, and you live somewhere that's generally a bit warmer than the UK, then the plastic gears between the motor and the digit drum have probably degraded into a jelly like substance.

[BristolE30]

I haven’t looked into this yet, and I don’t know the first thing to try but my myelomata stop the clocking up the miles any ideas? Thanks in advance

Assuming the speedo. is working as it should, and you live somewhere that's generally a bit warmer than the UK, then the plastic gears between the motor and the digit drum have probably degraded into a jelly like substance.

Hi Brian,

Could the SI batteries effect the speedometer? I noticed recently my speedo is flying erratically all over the place. Service lights are a little dim also...

[Brianmoooore]

SI batteries would only possibly affect the speedo if there was extensive corrosion from them leaking, an by that time, other things would have long given up.
Your speedo fault is likely to be cracked solder joints on the pins that connect the speedo assembly to the main circuit board (will be affected by thumping the top of the dash), or the wiring to the speed sensor near the diff.

[BristolE30]

SI batteries would only possibly affect the speedo if there was extensive corrosion from them leaking, an by that time, other things would have long given up.
Your speedo fault is likely to be cracked solder joints on the pins that connect the speedo assembly to the main circuit board (will be affected by thumping the top of the dash), or the wiring to the speed sensor near the diff.

Okay good to know thanks Brian! I’ll take it apart and have a go at resoldering it. Might as well replace the SI batteries also I guess

[rix313]

Tacho doesn't rely on the SI board batteries in any way, but the charging current for the batteries comes from the same power supply as for the tacho and temp. gauge, so when the batteries go short circuit they overload the power supply and affect the gauges as well.

So removing/changing the batteries removes the short circuit and causes the other gauges to go back to normal?

[Brianmoooore]

So removing/changing the batteries removes the short circuit and causes the other gauges to go back to normal?

That's basically how it works, yes.