dead instruments - popcorn fuse - MVAgusta.net
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post #1 of 20 (permalink) Old 01-14-2008, 12:34 PM Thread Starter
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dead instruments - popcorn fuse

First time on the bike in a couple of weeks, as it's been raining a lot lately... Everything was running fine, but about 30 minutes into the ride, right after I some hard acceleration the speedometer and and tachometer completely cut out. Everything else was fine (including the dashboard indicator lights for the turn signals, etc.), so I rode home.

I had the bike apart to replace one of the well nuts on the air intake about a week before, so I originally assumed that I pulled a wire loose and the acceleration jerked it free entirely, but the real problem is a blown fuse on the right hand side fuse box.

I tried replacing it, but every time I turn the key to the on position, it blows out.

I searched the forum for a few hours last night, and it seems people have a similar problem after improperly connecting the battery and blowing a diode on the left hand side of the bike... My battery did die a few weeks ago, and I had to pop start the bike, but I never disconnected the battery, so I'm not sure if the diode would have blown...

Assuming this diode is the problem, I still can't figure out why I'm blowing the pos. lamp fuse (this is 7.5 fuse, it's the third fuse down from the top of the box)... Most people with the blown diode seem to blow the instrument panel fuse which is a couple up from the bottom of the box.


If anyone has any advise I'd be really grateful. A good friend is picking up is Brutale this Wednesday I really want to have my bike on the road by then.


Thanks,

Wyatt Laikind
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post #2 of 20 (permalink) Old 01-14-2008, 01:55 PM
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post #3 of 20 (permalink) Old 01-14-2008, 02:27 PM Thread Starter
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For reference, here is the post by MikeF4UK regarding the diode I was referring to earlier. I just bought a multimeter to check the diode though, and this is not the problem (I AM getting continuity one way and nothing the other)... So I still have no clue what the problem could be. I replaced one of the well nuts on my left hand side air intake about the same time my battery died, maybe I pulled a wire loose by accident during that installation???

Again, any help is most appreciated.





"Try this: this is one I helped Dave Whattam (of Senna in mag with elbow down pic) with, I think you may have or had your battery in backwards, I have also included a PDF of the battery and connections, they are quite easy to get wrong:

Ok, in case anybody finds them self in the same position I did, the latch relay fuse (7.5 Amp) keeps blowing, this normally happens after a new battery of a battery going duff or being connected incorrectly.

The solution is likely to be a diode which is located behind the general relay.

The general relay is located on the gear lever side of the bike, take off the side panel, you will see next to alternator 3 square relays, held in place on a metal bracket (8mm bolt), remove the bracket and take off the left most relay from the bracket (rubber clamp just slips off), pull the relay away from its connector, turn the connector round and you will see a leg of wha looks like a bare wire, this is the diode, it goes between the blue wire and the grey wire, check the diode with a multi-meter on te "ohm" range, you should get continuity one way and nothing the other, (thats connect the positive to the blue and the negative to the grey and then vica-versa), if you get continuity in both directions the diode has popped. You can these from any local electronics shop, these diodes cost pence, get two as it always pays to be safe.

Whne you remove the old one make sure you note which direction it was connected, one leg of the diode will be shorter than the other, the new diode will have the legs the same length, match the new one up and then trim one leg to be shorter matching the existing one. Next cut or remove the old diode off, then either crimp the new one in place in the correct direction or solder it (like I did), thats it, but the bike back together.

If you want to check before putting tne new diode in, once you have rrmoved it, turn the igniton one, the fuse should not blow, if it does then you have another fault, but hopefully not.

I hope that the above proves useful to people and save them a huge amount of time and frustarion trying to figure out what has gone wrong

Regards

Dave"
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post #4 of 20 (permalink) Old 01-14-2008, 08:02 PM Thread Starter
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Hartley Hare, Are you around?
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post #5 of 20 (permalink) Old 01-14-2008, 10:58 PM
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9 times out 10 when you start blowing fuses shortly after working on a bike (especially when none of the work is actually on the electrical system) it's down to damage to the loom when refitting parts.

On the strength of that and from the details you've given I'd initally suspect that you have inadvertantly pinched/pancaked part of the loom when you have put the bike back together.

If you haven't done so already, I'd suggest simply retracing your steps, removing each part you did previously and visually inspecting the wiring loom as you go.

It may be prudent to take a resistance reading of the entire circuit so you have a base reference. It's fairly simple to do that, with the ignition OFF and the blown fuse removed, set your meter for resistance and stick one probe on a good grounding point and the other on the output terminal of the empty fuse holder. To be honest, I can't remember which side is supply and which side is output but as long as you have the ignition off (and you have a stock loom which nobody has pissed around with) you can just probe both, the one which gives you a fairly low reading will be the output side. Take a note of the reading. Keeping the meter connected can also be helpful.

The components powered from that particular fuse are side lights, relay triggers for both hi and lo beam, wheel speed sensor, fuel level sensor/sender and it also supplies the switched live for the dash along with live power for many of the warning/indicator lamps on the dash. So I'd pay particular attention around those parts/areas. While it's not common I have seen people pancake the fuel tank/level sensor part of the loom.

If you have a meter connected to the circuit keep an eye on the readings as you work along the loom, sometimes it can be quite difficult to see the damage so physically moving the loom can sometimes open the short circuit and your meter will show high or open resistance. If your meter has some sort of audible continuity test it's easier to just listen to the meter rather than watching it.

If you've done all that and everything checks out, let me know if you have done any other tests other than what you've mentioned thus far. Trying to track down a short circuit on a bike over the net can be horrendously difficult and on a circuit such as this which powers multiple different circuits/components can be very time consuming so if it's not simple loom damage I hope you have some patience.
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post #6 of 20 (permalink) Old 01-14-2008, 11:12 PM Thread Starter
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I have taken everything apart and put it back together once already, but I did was looking for more obvious shorts/loose wires. I'll do it again right now with the multimeter attached and see what I can find... If worst comes to worst I can always bring it into the shop, but I'm still having fun with it so I'll keep trying to for now.

Thank you very much for the advice. I have now read a lot of your earlier posts as well now, and they are all very informative.

-Wyatt
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post #7 of 20 (permalink) Old 01-14-2008, 11:36 PM
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If the visual inspection checks out and you're still up for the challenge leave the bike in bits as the next step will be to determine if it's a wiring or component fault (which doesn't take too long).
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post #8 of 20 (permalink) Old 01-15-2008, 01:13 AM Thread Starter
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I've gone over everything pretty thoroughly now (twice), and still am not seeing anything wrong. I tried adjusting the position of any potentially crimped wires, but still no change in the reading I get out of the empty fuse socket.

Would you mind explaining how I can determine whether it's wiring or a component fault?
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post #9 of 20 (permalink) Old 01-15-2008, 03:11 AM
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What are the resistance readings you are getting for the circuit? That fuse supplies live for a few components that even tho not physically powered up the circuit will still show relatively low resistance. Apologies as I should've noted this earlier.

Those components are the neutral, battery and side stand indicators and if you don't have a physical light switch on your left hand switch gear then the side lights and also the lo beam relay coil will also affect the resistance.

I don't know the exact resistance you will see if the circuit is under normal conditions but based on the assumptions that the warning lights are 1.5Watts and the lo beam relay coil is 100Ohms then...

If the bike is in neutral and the side stand is down and you don't have the ability to turn the lights off from the switchgear the circuit will read approx 9 Ohms.

With the bike in any gear other than neutral and the side stand raised it should read around 11 Ohms.

If you have the option to turn the lights off, then with the bike in neutral and side stand down you should see around 32 Ohms.

And with the side stand raised and the bike in any other gear other than neutral you should see around 96 Ohms.

These are just rough calculations in my head based on some assumptions. If I get some time today, I'll physically test these measurements with my own bike here and update/ammend accordingly.

If you are seeing a reading of less than 9 Ohms then the fault is still there. You also need to account for the internal resistance of the meter itself. Simply touch both probes together, note the resistance reading and subtract that from the readings you've taken from the bike circuits.

If you still have the short, then you'll have to disconnect the individual circuits/components and then recheck the resistance reading, if you are still seeing a short with everything disconnected then it has to be a fault within the wiring loom.

Obviously the tank is already disconnected, but you also need to disconnect the wheel speed sensor (the cable coming from the front sprocket cover), the left hand switchgear and also the dash. Assuming I haven't missed anything, this should basically just leave the wiring for the circuit and nothing else.

If the meter is now reading high or open resistance then the fault is within one (or more) of the components/circuits removed. And if the meter is still reading low resistance the fault is within the loom.

If it's determined that the fault is within one of the circuits/components let me know and I'll do some rough calculations for expected resistance readings for the individual parts.
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post #10 of 20 (permalink) Old 01-15-2008, 03:42 AM
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I've just noticed that the tail light is also powered from that circuit. For the purpose of testing I'd disconnect that completely, not sure exactly what wattage this lamp is but I'd guess it would show as a fairly low resistive load and will make testing for shorts very difficult if it's connected up.
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