Replace Volvo Penta LCD hour meter

This article is not strictly related to our boat, but could be useful for some other sailors. When bought our previous boat Catalina 25 with inboard Volvo-Penta diesel engine, the LCD hour meter on the tacho instrument was not showing any digits. This is a common issue with this tachometer made by VDO Technik AG. The issue behind this issue is the humidity and the corroded attachment of the ribbon cable to the LCD display. Someone fixed it by leaving the display on some heat and dried it, but this is just a temporary solution and the digits will go away anyway. It hasn't worked for me because only a fraction of the digits were visible after.
At least, however you can read the last motor hours before you replace it if this worked for you.
I wanted to fix it on our boat, but we sold her just before I could do that. However, my brother had the same issue on his boat. So I found this neat manual how to replace the display with an hour meter module that fits nicely into the instrument. The module I've used is Curtis Instruments hour meter module 701 series (12-48V) with 5mm tall digits for about 20 Euro.

original VDO Technik AG tachometer model: N 02 070 109

dissembled instrument

original LCD and the replacement module 701

I used the soldering iron and cut the rectangle hole into the plastic to fit the new module

fixed the module with hot glue gun

assembled and module connected

and it's showing hours again!

The cons of this solution is that the 5mm digit series modules are not backlit, which is not really important, but I hope that the hot glue will transmit some light into the module using the instrument's original backlight bulb. This was not tested yet.
The other downside is that the this replacement module is not able to detect if the motor is actually running so it can count some hours during the waiting for the river locks and so on. I think that even the original hour meter was designed such way, but I'm not sure. To avoid that, simply turn off the electronics when the motor is off. Hope this helps someone and don't be afraid to rebuild one of our self. I was done in less than 2 hours.

Updated 15.12.2014: The guy called himself Multihullgirl on Sailnet.com forum suggested a possible attempt to fix this issue, but as I said, it did not work for me. But you can try it first:

The LCD module is connected to the main circuit board via a flat ribbon cable. The problem is poor contact between the pads of the ribbon cable and the board receptacle. Lever up each end of the receptacle to release pressure on the cable and pull it out. Lightly clean the pads of the end of the ribbon cable with contact cleaner. You may also need to get a little contact cleaner inside the receptacle. Fully dry each with heatgun/hairdryer before reconnecting. Be careful when doing that as you don't want to overheat the ribbon cable.

Update 17.1.2017: Great tip from Anders Gustafsson, how to start the hourmeter only when the engine is running:

Stumbled across your page after already locating a curtis hour meter at Farnell. Anyway. To modify so that the counter only runs when engine is running. do as follows: On the module P goes to positive and N to negative. R (reset) also goes to negative. From the W spade terminal (usually nr 4). Run a wire to a suitable diode (I used an 1N4148, wire goes to anode, the cathode (denoted by ring) goes to an 1k ohm resistor (1/4W). The other end of that resistor goes to the cathode (ring) of a 9.1V zener. The anode of that zener goes to minus and parallell to that zener, put a 500nF ceramic cap. Run a wire from the cathode of the Zener to the I terminal on the counter module. Theory of operation: The W signal is AC, you rectify it with the first diode and clamp to 9.1V with the resistor and zener. The capacitor is just filtering. Result is a 9.1V signal whenever the engine is running. The docs accompanying the module are horrid, but at 12V, the module will start counting at approx 5.5V on the I terminal. The current draw is 42uA.

I've created a scheme for it: