MD2030 rev counter not working

[MM5AHO]

Rev counter seems to have died and I can't find a fault.
It has 12V supply to it OK, and I see about 8V AC on the signal from the alternator, but it sits firmly at zero.

Any ideas? What voltage should be on the signal from the alternator? Any tests I could do to check this out?

 

[VicS]

I believe 8 volts is correct.

Make sure all connections are good.

Did you check the supply between + and - connections on the instrument itself.

sounds as though it might have failed.

 

[FrancisRutter]

I had the same problem. I understand that the volvo rev counter is prone to doing this. I also understand, though I have not yet tried it, that If you get under it and dry it out carefully with a hair dryer, it will come back [for a while].
I solved it by putting in a fairly cheap counter from Northern Tool, put into the ignition circuit. That tells me the hours that the switch is turned on - much the same as the engine hours.
[I neede encouragement from Vic S to do the electrical work].

 

[VicS]

That was about the hour counter
Current question is about the tachometer itself.

 

[MM5AHO]

Thanks for replies. All connections are good, and cabling tested OK. The panel light inside the displ;ay lights OK, suggests 12V supply OK, and that verified by voltmeter on the terminals of the tacho itself.
The hour meter hasn't worked a long time, but not too concerned about that.
There is no intermittent working of the tacho, just dead.

Any suggestions for a replacement if Volvo parts are so expensive? Any others use this technique (alternator output) to indicate engine revs?

 

[earlybird]

Alternator driven marine tacho's have been a recent " buy it now" item on e-bay for about £50. He seems to be currently out of stock though. here
If you're into electronics, the basic tacho circuit is fairly simple. PBO described one, based on a standard chip, a while back. As long as your meter still functions electrically, that's the pricey bit.

 

[paulrae]

Yep Volvo tacho and hour-meter a rubbish bit of kit. You'll have guessed that Mine's goosed too. Like-for-like (but not Volvo) can be had from asap supplies . You can choose between one with and one without an hour-meter. Not cheap, but less expensive that Volvo, and fits the same hole.

Good luck