Volvo 2003 rev-counter problem on Moody 31

[AntarcticPilot]

AntarcticPilot - If you were closer I'd call over with an oscilloscope and a spare tacho to prove which part is at fault. Tricky to diagnose without seeing the actual signal as received at the back of the tacho. As Nigel says a small oscilloscope is handy for this issue - I think we both have the small DSO oscilloscope on board (available for just over £100).
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What do you think of the DSO 138 Oscilloscope kits? They seem to be pretty prevalent on eBay, and for boat diagnostic use they seem adequate - a bit basic for any serious use, but at the kinds of frequency and voltages that boat electronics use, they look fine. Advantages are they are dead cheap and therefore it isn't the end of the world if dropped in the water - analogous to cheap multimeters!

 

[Martin_J]

The 138 kit looks fun and I think I might have bought one if I had wanted an oscilloscope project in it's own right. Adding the cost of a power supply (or battery) and perhaps a better probe and then a case would add to the cost though.

Investigating the options a couple of years ago, a colleague quickly bought the DSO201 but we then realised that in my first radio project I needed something a little faster. I therefore bought the DSO203 and it has been very useful and being in a metal case seems to be up to the job of carrying with me for tasks on other boats.

 

[AntarcticPilot]

The 138 kit looks fun and I think I might have bought one if I had wanted an oscilloscope project in it's own right. Adding the cost of a power supply (or battery) and perhaps a better probe and then a case would add to the cost though.

Investigating the options a couple of years ago, a colleague quickly bought the DSO201 but we then realised that in my first radio project I needed something a little faster. I therefore bought the DSO203 and it has been very useful and being in a metal case seems to be up to the job of carrying with me for tasks on other boats.

Cases are widely available for the kit at around £5. They are a bit cheap and nasty, but they do the job. Power supply needs taking into account, of course. I was considering it because there is no way I'd be using an oscilloscope for anything except looking at low frequency signals, such as the output from transducers, or perhaps checking out signals on NMEA type buses. It's also over 30 years since I last associated with oscilloscopes, and even then it was being driven by a colleague, so a very basic unit would suit me.

 

[Martin_J]

Just one gotcha with the kit.. Seems to come in two versions - one with the surface mount parts already soldered and one without. As you say though - Once working it's a great tool for checking out alternator pulses and also which of the NMEA 0183 wires has the data on it

 

[AntarcticPilot]

UPDATE!

OK, there's nothing new to report - I was at the boat for the weekend, and we went out for a couple of days. No problem with the charging or the batteries; the alternator is definitely working in that respect, but the rev-counter remains as dead as a door-nail. No further investigations carried out, but I have ordered a DSO 138 oscilloscope (boys toys!) and will do more poking around after that has arrived and I've built it. I also ordered a signal generator (Velleman kit at £5, not an all-singing, all-dancing lab instrument!), partly to make sure the oscilloscope works correctly, partly to practise soldering before doing the DSO 138 and partly to generate a signal to test the rev-counter with an injected signal, as suggested above - the frequency is about right, I think.

I am quite surprised by how much I miss the rev-counter - I'd always thought of it as useful but not essential, but not having it makes it much harder to be sure the engine is doing what I think it should be doing.

 

[West Coast]

Re: UPDATE!

Antarctic Pilot, did you resolve your problem in the end? What was the solution? Am facing the same problem just now and so very interested in how you resolved yours

 

[AntarcticPilot]

Re: UPDATE!

Antarctic Pilot, did you resolve your problem in the end? What was the solution? Am facing the same problem just now and so very interested in how you resolved yours

So far, I haven't - more urgent jobs have intervened!

I bought on of the Oscilloscope kits mentioned above, but haven't succeeded in making it work yet - no doubt some tiny soldering glitch. The plan is to use that to check that the dignal from the alternator is making it to the control panel. If it is, then the rev counter itself needs servicing or replacing; I'll have to locate a suitable instrument maker. If it isn't, then I have to find where the break in the connection is!

 

[West Coast]

Re: UPDATE!

Thanks for reply, much appreciated.

 

[Stargazer62]

Hi,
I have the same problem with my rev counter on my moody 31. Did you find out the problem and repair it or did you have to buy a new rev counter?

 

[AntarcticPilot]

Hi,
I have the same problem with my rev counter on my moody 31. Did you find out the problem and repair it or did you have to buy a new rev counter?

No update yet - other things have intervened. See above!

 

[West Coast]

Sorted problem, turned out to be the alternator.

 

[AntarcticPilot]

Update - no movement on fixing the problem yet, but I have now got this:

Hopefully it will help me diagnose the problem!

PS, that's not the internal test signal, so don't worry about the lack of swquareness on the leading edges!