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Ticking off the common faults - speedo dead!

 
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Ben_nz
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Joined: 30 Sep 2003
Posts: 575
Location: Auckland, New Zealand

PostPosted: Mon Nov 13, 2006 11:37 am    Post subject: Ticking off the common faults - speedo dead! Reply with quote

Well great. I've got a track day next week, and out of nowhere my speedo decides to completely die. It had never given trouble in the past, but one juddery takeoff from the lights and it's history. Both the speedo and the odometer just sit there, no matter what button I push or how I whack the dashboard.
I checked the cable:
http://www.axys.co.nz/ben/alfa33/SPEDODIE/SPDOPLUG.JPG
The connections seem to be okay.. I measure a 340mV 120kHz sinewave whenever the ingition is on (even when the engine is not running), but this does not vary with the wheel speed.
I checked the sensor:
http://www.axys.co.nz/ben/alfa33/SPEDODIE/SENSOR2.JPG
but it looked like a black plastic rod and didn't tell me anything.
I pulled the dials apart,

and checked the connection with the speedo cable on the back of the dial cluster. This seemed fine, and it would have to be to let out the sinewave signal I measure in the engine bay. I pulled the speedo out to see how it was constructed:
http://www.axys.co.nz/ben/alfa33/SPEDODIE/SPEEDO3.JPG
There seems to be two motors fed from the same circuit board. A big one for the odometer (red and blue wires) and a little one for the needle (green, black and yellow wires). I measured only very high impedance on the pins which were exposed when I removed the needle motor plug.

But I don't have another sensor, I don't have another dial cluster and I'm not about to open the gearbox!
How does this horrible speedo work and what do I try next? Crying or Very sad
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tvatavuk
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Joined: 13 Mar 2003
Posts: 673
Location: Split, Croatia

PostPosted: Mon Nov 13, 2006 2:04 pm    Post subject: Reply with quote

0. Remove speedo sensor from engine/diff only when u must. It is delicate and u have more then 50% chance of damaging it when removing/installing.

You should get el. impulse from sensor with every rotation of wheel, number of impulses that is enough for 1km ot mile should be printed on label sticker somewhere on speed dials from back.

Usualy transistor or resistor fails, or both. Check soldering points on circuitboard and test them for signs of unwlding... use nose to smell board Smile

It is strange that is stoped working from rough start. This usualy points to lose connection somewhere or sensor getting out of diff. but you could be also suffering from broken conenction in flex board on back of instrument cluster.
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Little black dress which replaced Alfa Romeo 33 S 16v Permanent 4 GMo
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matt33
Alfasud


Joined: 29 Jun 2005
Posts: 72
Location: South Staffs

PostPosted: Mon Nov 13, 2006 7:59 pm    Post subject: Reply with quote

Hi Ben
I have got a spare (used) instrument cluster if you are interested.
I dont want any money for it, if you want to pay for the postage from the u.k, its yours!

Cheers
Matt
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Ben_nz
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Joined: 30 Sep 2003
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Location: Auckland, New Zealand

PostPosted: Mon Nov 13, 2006 11:38 pm    Post subject: Reply with quote

Speedo sensor doesn't look delicate. Confused
It must break internally from impacts or something, in which case I imagine it'd break if you wheel hopped the car under acceleration or drove on very bumpy roads..

I'm organising with a garage to swap some parts to try to find the trouble, but if I'm likely to break the sensor then maybe I should let the mechanic change it on his hoist..

-Ben
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tvatavuk
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Joined: 13 Mar 2003
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Location: Split, Croatia

PostPosted: Tue Nov 14, 2006 11:35 am    Post subject: Reply with quote

I know it doesn't look but when AR factory says in its manual after removing & putting it back, if speedo stops working to replace it, it must be some problem.
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Tino Vatavuk
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Ben_nz
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Joined: 30 Sep 2003
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Location: Auckland, New Zealand

PostPosted: Mon Nov 20, 2006 7:14 am    Post subject: Reply with quote

The garage found that both the speed sensor AND the instrument cluster were faulty.
And yet somehow I wasn't surprised. Rolling Eyes

So they've fitted a working speed sensor, but I won't be able to have someone repair the instrument cluster in time.
Where are the parts that usually fail, are they on the board which sits on the back of the rev counter, or the board that sits in the speedo itself?
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
Posts: 388
Location: Paris, France

PostPosted: Mon Nov 20, 2006 8:49 am    Post subject: Reply with quote

Hi,

as far as i know there are two causes of dying speedoes on 33s :
1st : electrical shock ; this occurs when some cowboy tries to jumpstart the car using a booster (higher voltage than supported by the unit). This is not repairable as the fried chip is custom development and not available at an electronics store.
2nd : it's due to poor contact, most of the time between the speedo board and the harness. The connectors here are crap and the signal level from the gearbox unit is very low. A few milliohms extra contact resistance will be sufficient to kill the signal. So, the rule of thumb is to get the best electrical line between the sensor and the speedo. I solved my problems after much trial & error tests, by finally hooking the sensor directly to the speedo, using a shielded wire and soldered connections at both ends.
A few pics can be found here : http://alfaimola.free.fr/technique/electricite/compteur/index.html

regards,
zp
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Ben_nz
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Joined: 30 Sep 2003
Posts: 575
Location: Auckland, New Zealand

PostPosted: Mon Nov 20, 2006 11:51 am    Post subject: Reply with quote

Zenith, the Google English translation of your page is amusing: "Here the speedometer, it is equipped with a chart girl." (Cool! Hope she's cute...)
"And veiled a repair which twists the neck definitively with all the problems of whimsical meters.." Wink

It looks like the series 3 circuit boards are different from those in series 2 cars though. Sad
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Ben_nz
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Location: Auckland, New Zealand

PostPosted: Wed Dec 20, 2006 9:24 am    Post subject: Reply with quote

Well, I finally twisted the neck definitively with the problem of my whimsical speedo.
I found someone wrecking a 33 and bought the instrument cluster for $30. I transferred both circuit boards onto my original instrument cluster and it started working again. Rolling Eyes

So all I can say for sure is that the speedo and odometer motors were never faulty, and that I hate Alfa electrics. Evil or Very Mad
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Ben_nz
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Location: Auckland, New Zealand

PostPosted: Fri Jan 05, 2007 12:13 pm    Post subject: Reply with quote

Guess what?
Speedo stopped working again already. Evil or Very Mad
I swear this car is ten kinds of crap sometimes. I've spent the last two days sanding and repainting rust and the rear and side bodykit skirts, and this is how it treats me. Evil or Very Mad
I only managed 250km since I last fixed the speedo - not far enough to know whether rebuilt carburettors has improved my fuel economy!

I now have to consider the possibility that a problem with my original speedo motors has caused both the original and replacement driver boards to fail. Or maybe something completely new has gone wrong. Rolling Eyes
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icky
Alfasud


Joined: 20 Mar 2003
Posts: 70
Location: Lismore NSW Australia

PostPosted: Sat Jan 06, 2007 12:48 pm    Post subject: Reply with quote

Ben,
Have you gone through and remade all the connections?
A very common fix is to ditch the connector to the circuit board and solder or even screw the cable straight to the board. Vibrations can move it loose.

Also check that there isn't a high current cable running alongside the speedo cable, my thoughts are that induction can cause fluctuations seeing that it works on a small milliamperage, my wiring is a bit shot, hence when the speedo dies pressing the rear demister button brings it up again Rolling Eyes
Don't know if this works because of something electrical or whether the movement of the switch jars a connector or something. I just call it Italian Character... Beats thumping the Dash. Razz

Cheers
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Ben_nz
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Joined: 30 Sep 2003
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Location: Auckland, New Zealand

PostPosted: Mon Jan 08, 2007 9:55 am    Post subject: Reply with quote

Yes, unfortunately I have checked all the easy stuff. I've cleaned the connectors with electrical contact cleaner, metal polish or by grating at them with a knife, and I've bent the pins of the plugs back into place using a small screwdriver, so they grip firmly and make the best connection possible. I've measured the resistance of the connections using a multimeter.

I do not want to remove the plugs and solder the wires onto the circuit board, because then I'll never be able to take the instrument cluster out when the next part of it goes wrong!
For example my voltage gauge suggests that the alternator does not work without the instrument cluster connected. Confused

We are predicted to have rainy weather for the rest of the week, but I will start looking for what might have gone wrong as soon as possible.
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Scott Sander
Alfa 33


Joined: 20 Feb 2003
Posts: 419
Location: Sydney, Australia

PostPosted: Mon Jan 08, 2007 2:00 pm    Post subject: Reply with quote

Ben_nz wrote:
I do not want to remove the plugs and solder the wires onto the circuit board, because then I'll never be able to take the instrument cluster out when the next part of it goes wrong!


On my series 1 I tried all that you have tried, ended up finding suitable points on the back of the cluster then a short length of wire to a connector and replaced the original connector so it then fitted the new connector. I could then remove the cluster if needed. Unfortunately I did such a good job I never had to remove the cluster again. Wink

It is looking like I now need to do the same with my 16V.
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Ben_nz
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Location: Auckland, New Zealand

PostPosted: Sat Jan 13, 2007 3:01 am    Post subject: Reply with quote

I jacked the car up today, put it in 5th gear and tried to measure the output of the gearbox sensor while I increased wheel speed to about 70kph.
I couldn't measure anything between any of the three wires using either the 200mV DC scale or the 2V AC scale of my multimeter.
Unfortunately I never tried this last time the speedo actually worked, so I don't know what I'm expecting to find.
Can anyone tell me how to measure whether this sensor is working?
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Scott Sander
Alfa 33


Joined: 20 Feb 2003
Posts: 419
Location: Sydney, Australia

PostPosted: Sat Jan 13, 2007 3:28 am    Post subject: Reply with quote

Ben_nz wrote:
I couldn't measure anything between any of the three wires using either the 200mV DC scale or the 2V AC scale of my multimeter.


Usually when a sensor has 3 wires it means that there is a ground wire(black), power wire (12V, red), and a signal wire (white).

Looking at the photos you have previously posted this would seem the case. You previously mentioned that the tacho was not working. From that I would say you are either not getting the 12V power or the 0V for the ground to the instrument cluster.

So check that you can get continuity to ground on the black wire (remove battery first) and can get 12V on the red wires when the sensor and other connectors are connected to the instrument cluster.
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Ben_nz
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PostPosted: Sat Jan 13, 2007 4:12 am    Post subject: Reply with quote

There's really only two wires - red and white. The two-core sensor cable is shielded, and the two sections of cable between the sensor and the dash have their shieldings connected through the engine bay plug. The shielding doesn't connect to the dash circuit board at all.

Looking at my spare instrument cluster, one of the two sensor wires connects to ground and the other connects directly to a chip, via what must be a pull-down resistor.
This suggests that the gearbox sensor isn't powered by the instrument cluster. It must be some kind of electromagnetic deal where a voltage is generated in the sensor by a passing bit of gearbox/differential.
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Matt Stolton
Alfa Sprint


Joined: 14 Mar 2003
Posts: 233
Location: London

PostPosted: Sat Jan 20, 2007 5:43 pm    Post subject: My Speedo Reply with quote

My speedo died once, and I found it to be the wires that go to the motor that actually drives the needle, from the PCB.

Because the wire kinks 90 degrees to fit inside the housing, it breaks and stretches (at least it did on mine). I replaced both + and - motor wires, and routed them in a more kind manor to stop a reoccurence, basically they are too short and tight in the original.

May be a quick and cheap thing to try, and easy to measure the continuity from one end of a short cable to the other.
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Ex Alfa 33 'GTA' (P4 with Knobs On)
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Ben_nz
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Location: Auckland, New Zealand

PostPosted: Sun Jan 21, 2007 10:55 am    Post subject: Reply with quote

If that were the case with my car, the odometer would still be working.

I've given up, cos I'm out of known working parts and don't have the tools or info to test further. I suspect the recently installed gearbox sensor is dead already.
I'm taking my horrible car to a specialist speedo repair place tomorrow. Mad
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Ben_nz
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PostPosted: Fri Jan 26, 2007 11:03 am    Post subject: Reply with quote

$220 later, my speedo is working again. Rolling Eyes
The gearbox sensor hadn't failed this time, just both of the second hand boards two weeks after I installed them in my car Exclamation
They'd been working for eighteen years or so before they fell foul of...
ShockedThe Curse of the Black CloverleafShocked
Speedo fixing man couldn't or wouldn't tell me which parts had failed, so I opened up the instrument cluster to see what had been replaced. Many components appeared to have had one leg removed for testing, but only the tall transistor on the speedo drive board and a diode on the back-of-the-rev-counter board appeared to have been replaced.

So it's working now... but - for how long? Wink
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Bellamachinna
Alfa 33


Joined: 12 May 2003
Posts: 352
Location: Lisbon-Portugal

PostPosted: Fri Jan 26, 2007 6:53 pm    Post subject: Reply with quote

Hi...

On my experience, it will not take long, to fail again... Confused

My 16v, had already gone through 4 different clusters... And they all failed...

The current one, is the original from the car, that i took to be repaired, but is also starting to go...
On engine start up, the needle goes to 60 km/h, and falls back again. Driving the car, sometimes i look at it, and its dead (no speed at all). Passing through a hole brings it back to life...

The gearbox sensor was replaced 8 months ago, when this repaired cluster went back to the car...

I think you are right... Our Alfas are cursed... Laughing
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mo99
Alfa Arna


Joined: 14 Oct 2005
Posts: 12
Location: Canterbury, New Zealand

PostPosted: Mon Jan 29, 2007 10:23 pm    Post subject: Reply with quote

I am liking my mechanical speedo on the sprint more and more. When the cable comes off at the gearbox it only takes me two hours on the ramps to put back on Wink (Inboard disks) Evil or Very Mad But at least it works
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truepiece
Alfa Arna


Joined: 17 May 2005
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Location: Athens-Greece

PostPosted: Fri Mar 02, 2007 2:09 am    Post subject: Reply with quote

Hi,

After working a lot on my speedo I have some suggestions. Smile

If the speedo works when passing through holes etc there can't be a faulty electronical component. In that case it wouldn't work at all.


So it could be:
- poor contact on the two connection points (on the cluster and next to the battery)
- wire that is cut internally, the signal from sensor never reaches the cluster
- "cold" soldering of some component on the pcb

It is extremely unlike to be:
- sensor
This device has no moving parts. It contains only a coil that is wraped around a permanent magnet. It is a faraday effect-based voltage generator as benz_nz mensioned. Considering that the current that flows is very low that can't burn the coil, how could the sensor possibly be damaged or be so sensitive?

Suggested tests are:
- Check continuity between the connector behind the cluster and the one near the battery.
- Disconnect the sensor and measure its resistance (black-white, not the shielding). You should get a finite resistance (the coil's resistance). If not, you have bad wiring between sensor and connector, not neccesarily a damaged sensor. Of course, if you replace the sensor it comes with a new cable, so you think that it was a sensor failure.

-Clean all contacts and make sure every connections is firm. If in doubt, solder directly on the pcb or change connectors with more reliable ones.


I had a poor contact problem. After fixing the connectors the speedo worked for over a year until recenlty, when it died again. I also had some strange behavours like the needle jumping from 40 to 90 when moving. All these were due to bad sensor wiring. When accidentally the wire made contact, it sent some random pulses that confused the speedo. Restored the wiring and now works fine.

Sorry for any bad english Embarassed
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Ben_nz
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Joined: 30 Sep 2003
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PostPosted: Sat May 23, 2015 11:02 am    Post subject: Reply with quote

Bellamachinna wrote:
On my experience, it will not take long, to fail again... Confused


You know what? This guy was right. I stopped replying to this thread a million years ago, but my speedo did soon become intermittent again. It was then increasingly useless for years, responding less and less to the rear window demister button until it just didn't work at all. Although I could use the rev counter for a speedo, I got sick of that and eventually devoted more time to finding the problem. It was this:

(in case I delete that photo one day, it showed a connector to a circuit board on the back of the instrument cluster).
The connector wasn't unplugged, the solder joints weren't dry, it was just a rubbish connector. Rolling Eyes
Now the wires are soldered and the speedo has worked 100% of the time for about 1000km and counting. Very Happy
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paulhide
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PostPosted: Sat May 23, 2015 10:06 pm    Post subject: Reply with quote

8 years later Exclamation Great work Exclamation
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Ben_nz
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PostPosted: Sun May 24, 2015 7:34 am    Post subject: Reply with quote

Yeah, I never thought I'd own this car so long! I bought it in 2003 when I had just turned 24 and crashed my first car, so I needed something cheap to buy and insure. Now I keep throwing money at rust repair and the rest of it mostly holds together, so although it has been relegated to a weekend car, I'm still heel-and-toeing this relic from the '70s around like the same old menace to society. Cool


(only a 33 can go that fast standing still, due to brilliant Italian electronics)
http://www.axys.co.nz/ben/alfa33/suedewheel1.jpg
http://www.axys.co.nz/ben/alfa33/me_and_sprint_2s.jpg
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