Blowin main fuse on 82 GS550LZ

[Anonymous]

I need some help here.

the main fuse has blown, and keeps blowin. To accomplish this at least the brain, and either one or both coil must be connected and the key position on. the ignition fuse must be in, but not the other two.

this bike is totally stock. I have taken most of the bike apart trying to track down the problem with a good Fluke multi meter, but just can't figure it out. Everthing I look at looks factory new, no fraying or problems have been found.

Some other interesting features I have found: The resistance to a lot of stuff is surprisingly variable over a wide range, like the rear tail light, why the hell can that be?

the coils both check in spec on the primary, (3.8 v 3 - 5 ohm), and one is in speck 34K (v 30-35) on the secondary and the other gives variable readings, but THIS IS PROBABLY NOT THE CULPRIT, since either coil can blow the fuse alone, without running the engine.

The fuse does not blow if no coil is hooked up, if the key is off or if the brain is disconnected. Runnign the engine will blow the fuse if for some reason it won't blow some times by just being connected.

the starter relay is in spec, and that is not in the fused circcuit . starting is not required to blow the fuse.

another weird thing happens, if the fuse seems OK temporarily, it can sometimes be blown by simply disconnecting and reconnecting the power to the fuse block. So the intermittent nature makes it even more fun to diagnose, does the fact that it is intermittent point to a particular culprit, like the brain? Suzuki calls this the Igniter unit part no 32900-47320. And in case you don't know this already, I have a tip for everyone .... you can see the parts schmatics on the net for lots of bikes, including GS's at http://www.bikebandit.com/partsbandit/shopindex.asp?

Any ideas would be greatly appreciated.

I hope I don't have to start guessing by
replacing parts. For example the brain alone runs about $318.16. Can that be troubleshot? It has a bunch of weird resitances, does anyone know the specs to check that out?

Thank you VERY much!

[Anonymous]

Probably your ignition unit has broken down; can't tell for sure, but you can test the transistors that switch the coils, with your meter.
Disconnect the power, either with your ignition switch or by disconneting the battery (safer). Set your meter in diode test mode, disconnect the coils from the ignitor. Connect one meter lead to one of the the output leads of the ignition unit, connect the other meter lead to ground. You should read either high resistance or just a few ohms of resistance. Reverse the meter leads. You should read a significantly different value. If you first measured low resistance, you should read high resistance now. Otherwise, if your first measuring gave a high reading, you should measure low resistance the second time.
Same procedure for the other output.
If your meter shows low resistance both ways, your switching transistors have blown. That causes the fuse to blow. If the readings showed correct values, there is still a chance that one or more of the other transistors (there are two more) in your ignition unit have been destroyed. Since they don't switch a lot of power, that chance is slim though. They can be measured the same way by connecting the meter leads to the +(power) lead (disconnect it first!) of the ignition unit and ground. If you conclude that the ignition unit has blown up, check your coils again! There must be a reason for the ignition unit to blow up!
As for the different readings at your tail light, that could be a bad ground connection. Clean the connections and it should be OK. As long as the tail light works fine, don't bother.

Jojo

[Anonymous]

thanks

Thanks jojo, I will try this soon.

I think I figured out the lamp thing....at first the lamp is cold, but then heats a little from the testing voltage, then as it warms the resistance rises..which draws more current, .and this process keeps kickin itself in the hinie ....

[Anonymous]

I had a niggling problem with my '81 GS550 where I blew main fuse after main fuse... It turned out to be a (probably intermittent) dead short in the stator. It'd be OK ... then I'd start cranking and it'd start for a second, then the main fuse would blow. I dropped all the other fuses down to 5A to try to get them to blow "first" ... but no luck. Always the main.

You could test this by disconnecting the stator from the regulator. All 3 phases. If you can start & not blow fuses that way, you're in the same boat I was. You can also check for shorts between all 3 of the stator leads and ground. There should be infinite resistance between the stator lines & ground.

I gave my money to electrex and got a new stator & regulator. Everything's been fine since.

--Mitch