Messing with MFA and Eco gauge

I just doubled checked the resistors and found one hidden out the way, its sits next to that round adjustable capacitor and it's dead! I'm hoping that this could the problem! otherwise its back to those four microchips.

maybe - but why would this one resistor fail on so many circuit boards ….. I can (sort of) understand wholesale failure of the processors after 25 years - they were cheap to start with and are now time expired but one resistor….. maybe…..but just doesn't feel right.  Could be a co-incidental problem.

Tell you what - send me spec / photo / drawing … something so I can identify the exact unit and I'll strip down (how many have I got… dunno… 1/2 dozen?  something like that) a colection of clusters and see if this is a consistent fault.

MP

You're probably right M, but I want to explore every avenue before moving onto the micro chips. My digital camera is out of action at the moment so I can send or upload any pictures, but the clocks I stripped down are VDO.

If you can test that component, its next to the adjustable capacitor, near to the rear of the lcd.

Cheers

I'll strip an unit on Saturday and take a couple of photo's and post' em     (I've got one of those camera's with a phone on it - sems to work OK) to make sure we are on the same page then I'll ask my electronics guys to test the board and the specicific component.

MP

All you need is a mulitmeter and set it to resistor, then touch each end to see if any value registers. I wouldn't go out of you way and pay money unless its a free be :wink:

Lhasa

Do any of these help?  Which component matie - assuming they do…(help I mean)

My board is different, mine has got a big black thing in the top left hand corner and has the black plastic rod attached to it that switches from position 1 to 2 (which when fitted protrudes through the plastic Perspex)

I've only got one panel, are they mk2 gti clocks?

It should have 8 pins at the top that goes through the plastic housing into the blue plastic printed curcuit. The same is true on my motormeter clocks as both clocks share the same pin arrangement. Also your board has a cmos back battery which is the round vertical thing on the left hand side. How strange?

I just wondered if that is a panel from 1600 Gti clocks?

On the back of my panel is VDO 832.

If they are mk1 1800 GTI clocks, but just a different variation, the theory of the resistor goes out the window and its likely to be one of the micro chips.

Time will tell.

I'll strip another set - VDO's with the the plastic rod that switches from Position 1 to Position 2

Its ok M, the resistor has a high value and its working, I just changed the setting on the multimeter, its also working in parallel with the crystal oscillator. I think it powers the display and that the adjustable capacitor probably adjusts the contrast. All the components seem to be working, I don't know about the chips though. In an ideal world you would just replace the board with a new one but these probably are obsolete.

I still havn't given up and am working on the idea of clean up the board and checking for any dry joints.

I was just wondering if the 99.9 and -31 problem is unique to the VDO clocks?

Ok - saves me stripping another set of clocks!  Well done.

Three points:

1.  the VW workshop manual states (a) replace G55 unit and if this is not successful (b) replace board - if I recall correctly - just don't have the bandwidth the check this but I am sure my recollection is accurate

2.  Yep - you guessed it - the borad is o-b-s-o-l-e-t-e as is the G55 unit

3.  Afraid not - this problem is as evident in the Motometer units as the VDO units.

I still think it is the processor but not sure.

Do you have a set of clocks in the vehicle?  If so, try this:

Set MPG reading to 0.0 (works on mine).  Roll car down a hill - ignition ON engine OFF (ie power to dash) - see if reading stays at 0.0.  This will eliminate the input from the hall sender on the speedo as being the problem (vacuum zero).

Set MPG to 0.0, and drive vehicle - and see when MPG setting trips to 99.9.  This will confine the error to the vacuum input / G55 unit / circuit board.

MP

I'll try that M.

Today I removed my fully working Motormeter clocks from my car and fitted just the blue plastic and the lcd panel from the faulty VDO , nothing else and the reading on the outside temp was still -31, after pushing on the blue plastic printed circuit the reading changed to 14. So I'm just wondering if that fragile printed circuit has anything to do with it?

As it happened when I refitted the fully working Motormeter clocks the red oil light failed to come on, but I traced this down to one broken joint on the blue plastic going onto the speedo. I repaired it with some wire and solder.

That blue plastic printed circuit is the pits!

That blue plastic printed circuit is the pits

How hard would ot be to make up a new loom for the clock back?

It certainly a very good idea, worth having a good think about........

Or use some MK2 clock rears ? I am fitting some in my MK1 20V and have wiring diagrams now for both sorts of clocks . MK2 item is easier to get hold of but does not have the gear change light or vacuum guage .

Hmmmm - Lhasa you could be right.

Are we chasing two problems in one thread?  (temp + MFA)  

Outside temp does not seem to be a common problem ……. but interesting that you had a fault in the blue circuit loom … let me think about this

M

chudd said

Or use some MK2 clock rears ? I am fitting some in my MK1 20V and have wiring diagrams now for both sorts of clocks . MK2 item is easier to get hold of but does not have the gear change light or vacuum guage .

Was thinking of doing this myself to restore my mpg reading on mfa - not too worried about the economy gauge/light, which was always a bit of a pita when working!
Also…doesn't the Mk2 have sensible blue mainbeam warning led??? Much better colour - even the early roadtests in the seventies used to commnet on the weird idea of a yellow main beam lamp!

Oldfart said

chudd said

Or use some MK2 clock rears ? I am fitting some in my MK1 20V and have wiring diagrams now for both sorts of clocks . MK2 item is easier to get hold of but does not have the gear change light or vacuum guage .

Was thinking of doing this myself to restore my mpg reading on mfa - not too worried about the economy gauge/light, which was always a bit of a pita when working!
Also…doesn't the Mk2 have sensible blue mainbeam warning led??? Much better colour - even the early roadtests in the seventies used to commnet on the weird idea of a yellow main beam lamp!

Not sure about the main beam light ? Will let you no .

Waiting for some MK2 clocks to be delivered to see how difficult they will be to fit .

Are these from mrk 2 clock?
I just wondered if that is a panel from 1600 Gti clocks?

No and no I am afraid - imprinted on the board is 1.8i 82 kw


Another mystery…

M