*** CURED ***
Well, I was unable to source a good used replacement rev counter...
I contacted the Alfa / Fiat dealership in Welling, mainly to see if the PCB was available as a seperate part, it wasn't, but I was qouted £280 for a complete new rev counter and it would have to be ordered from Italy!
So, I decided to have a bash at repairing my unit and ordered a pack of the VND810MSP chips from RS.
There are 3 of these chips on the PCB, but after doing a little research it seems that 2 of them seem to cause most of the trouble.
I found some pictures on a Polish Alfa forum showing some rev counter PCB's with the lower right and lower left chips blown, to the point that the PCB underneath them had scorched quite badly!
Luckily, there was no damage to my circuit board.
The VND810MSP mounted towards the centre of the PCB doesn't appear to be as troublesome.
The chips themselves, are a 10 pinned surface mounted device... the pins are very small and are very close together, so I bought the finest needle tip for my 18w soldering iron. I used my gas powered iron with a fine tip for unsoldering and soldering the larger tabs either end of the chip.
This isn't a job for the inexperienced, as it would be all to easy to damage the very fine printed circuit, but luckily I have a lot of experience of this type of job... 21 years as a TV engineer in a previous life!
With the chips replaced, I put the rev counter back in the car, replaced the fuse feeding the rear light cluster and connected my meter to the battery... 25mA
I pulled the bulb to make sure the bulb warning light was working and it was!
So, for the grand some of around 13 quid, I'm all back up and running!
Thanks to all who replied!