3B rev counter feed wire voltage?

[gmac78]

Hello all,

Needing a bit assistance from those in the know.

Ther old girl is ever so close to going back on the road after a period of almost 2 years in the garage.

However, after starting her up from a prolonged period of hibernation my rev counter does not work.

I tried a mulitmeter across pin 22 green/blue wire on yellow connector (rear of cluster) and when idling it was reading 4-5v, a small blip of the throttle seen the voltage rise to 6-7v.

Is this method correct for determining signal from the feed wire? as my rev couter still does not work. I think i read somewhere that an oscilloscope had to be used but perhaps i've got mixed somewhere along the line.

All the dials have been replaced in the past so no issues there.

Any help or tips greatly appreciated.

Thanks
Gordon

[gmac78]

bumpty bump. Any ideas for me guys?

[newsh]

The signal goes through some pin and socket connections between the circuit boards inside the cluster. There is probably a little corrosion on the pins. You can dismantle the cluster and clean the pins and gently nip up the sockets. This is what fixed mine.

[UrS4boy]

G22 Vehicle Speed Sensor (VSS) and G21 Speedometer info

I would have thought 0-5V but I don't really know (never needed to know).

As newsh suggests, probably corrosion between the G22 Vehicle Speed Sender harness connection to the connection to the G21 Speedometer and all points/connectors in between.

Here is info about the G22 and G21 that I do know:

http://forums.quattroworld.com/s4s6/msgs/168463.phtml

[gmac78]

Alright right guys thanks for the pointers, i'll strip the rev counter down to see if i can find an electrical gremlin hiding on me. I hate electrical issues so i do, most frustrating trying to figure them out!!

[UrS4boy]

G28 Engine Speed Sensor info

Alright right guys thanks for the pointers, i'll strip the rev counter down to see if i can find an electrical gremlin hiding on me. I hate electrical issues so i do, most frustrating trying to figure them out!!

Sorry. The penny just dropped. You were talking tachometer (rev counter) NOT speedometer (tachometer auf deutsche). D'oh!!!

Okay, re: G28 engine speed sensor, see this info (make sure you scroll down to the bottom to see the wiring diagrams):

http://forums.quattroworld.com/s4s6/msgs/20986.phtml

[gmac78]

Ah right that's a bit better now, cheers mucker! I thought you might have got confused with the earlier info on G21/G22 sensors. I wonder if these wiring diagrams are suitable for the 3B model? as i'm fairly sure i read on here that pin 22 on the yellow connector (rear of cluster) is the rev counter feed wire.

Unfortunately I'm working offshore now so won't be at home for another few weeks to have a closer look, arrrgh! At least i'll go home armed with some new found knowledge.

[UrS4boy]

B3/B4 G5 Tachometer (rev counter) wiring

Ah right that's a bit better now, cheers mucker! I thought you might have got confused with the earlier info on G21/G22 sensors. I wonder if these wiring diagrams are suitable for the 3B model? as i'm fairly sure i read on here that pin 22 on the yellow connector (rear of cluster) is the rev counter feed wire.

And here is more (and it might make your head hurt).

Download this 3B wiring pdf from S2Central.net:

http://www.s2central.net/S2_Schematics/A/A17.PDF

Scroll to Page 3/17 to find the G28 engine speed sensor.
Note that it enters the J220 Engine Control Module (ECM or ECU) at pins 47/55 and 48/55. These wires get there via a grey three pin connector in the engine bay (T3g), pins 1 and 2. We don't immediately see how that signal gets to the rev counter (be patient, it is coming).

Scroll to page 8/17

You will see the G5 Rev counter (tachometer)

It has two inputs:

1. green/blue wire from track [91] on track [84]
2. brown/black wire from track [107] on track [85]

Scroll to pg. 9/17

On track [91] you will see the green/blue wire going to track [84]. Okay. But ???
BUT you will also see on [92] a connection to a violet wire that came from track [56] via Pin 7 of a black T10 connector in the auxiliary relay carrier (under the dash??)

Scroll back to pg. 6/17 to pick-up track [56] violet wire

Ah, ha!! The violet wire that goes to track [92] comes out of the J220 Engine Control Module (ECU) at pin T55/6. Finally we see the connection between the G28 engine speed sensor and the G5 rev counter.

To complete the story, scroll to page 10/17 in the pdf.

There you will find [107] brown/black wire connecting to T26b/3 on the J189 Autocheck module. Not sure what that does and least we've tracked everything.

I trust that redeems from the earlier G22/G21 confusion.

[gmac78]

It's fair to see you have fully redeemed yourself, good detailed post there. Thats given me plenty to get my head round, nice light reading before bed time. Cheers dude.

[gmac78]

Right guys, i'm pulling my follicles out with this one. I'm determined to get to the bottom of it without having to buy new clocks, i don't like being beaten by what is something quite simple if electronics were your back round.

Ok, i have removed the rev counter unit from the clocks and re-soldered all the joints, they all looked in good condition with no cracks present but at least that is eliminated. I still can not get the rev counter to move when applying voltage across pin 22 feed and pin 23 ground (yellow connector). However, if i apply voltage directly to the coil of the rev counter it moves no problem????

I assume the fault lies within the small circuit board of the rev counter?

One thing that i have noticed is if i apply 9v from a battery to pin 22/23 i only get 0.2v out the other end of the circuit board were it connects to the coil for the rev counter. 0.2v is simply not enough to move the rev counter, however if i apply 1.5v from a AA battery directly to the coil it moves.

I've attached some pics of the circuit board, is there anyone with an electronic back round that can tell what might be causing such a small voltage at the green/red wires that connect to the rev counter coil when 9v is applied to pins 22/23 9 yellow (connector).

Any help is greatly appreciated.

[domas]

did your resolder the whole backside of the little pcb? no? do it and do the that for the whole cluster as well

[gmac78]

Hi domas, yes i re-soldered all joints on the rev counter PCB and main board, however I think the problem appears to be on the small PCB, not 100% on that one though.

Check this link out, the PCB looks very similar, i'm not sure if an S2 rev counter should behave in the same fashion?

http://www.youtube.com/watch?v=utRHGSNuzDY

[domas]

no ideas really. Those dash inserts do not have their schematics available anywhere, so the only thing i can suggest is the standard ways - cold joints and sometimes dry or bulged electrolytic caps.

does the tacho needle show no activity at all when driving normally?

Else, try sourcing another pcb from other petrol b3/b4 models, i guess the tacho range is the same? I mean it travels the same amount of degrees to show specific rpms?

[S2central.net]

Have you checked there is actually rpm signal coming from ecu ?
And that continuity from the ecu pin to the cluster is good ?

[andy10v]

We tried the clocks in my car, still did not work.