smoking diode block

Started the 750rh for the first time today and the diode block started smoking. Anyone know how to trouble shoot the little black box.

 

At small risk of hijacking this thread...I'd like to add to the question. Mine isn't smoking, but it is clearly damaged and I think is causing other problems.

+1 on how to check it....also, what does it do, and do you need it if you have the safety switches bypassed? (Don't worry...I don't have a kickstand to leave down!)

Any more questions I'll start my own thread.

 

It looks like the Seca 750 diode block has two purposes.

1. Rectify from White wire from the alternator to White/Blue to trigger the headlight relay.

2. Ground the Blue/Yellow signal from the sidestand relay when the neutral switch is closed (through Light Blue wire).

If it's smoking it's probably toast. Do you have a meter with a diode check function? I would think it wouldn't just die, though, and probably would have been damaged by being miswired somewhere.

I think it could be replaced with a couple of rectifiers. One between White and Blue/White, with the anode on the White side. And another between Light Blue and Blue/Yellow with the anode on the Blue/Yellow side. 3A should be plenty for these... 1A might even be OK. If there's a wiring problem, or a bad side stand or headlight relay, though, replacement rectifiers will smoke too.

 

I do have a meter with a diode check function...but couldn't figure out how it worked ($4.99 from Harbor Freight). I tried all sorts of combinations across the diodes...it seemed to be reading just like a Ohmmeter.

 

Don't know if my meter has a diode check but will look tomorrow.

It is possible i switched a wire someplace or that I didn't catch an already mis-wired section but at least I have a place to start now. And I can use regular rectifiers to test instead of burning up diode blocks

 

Get a wiring diagram, it will show you the arrangment of the diodes. Since there was smoke its probably toasted. Those old diodes tend to crack and burn , there is a good chance nothing else is wrong. You can get one on EBAY for 20$ or less, it is used so you might get a bad one. There are just a couple of diodes in there and they can be easily replaced( Radio Shack 1N4001 rectifier diodes work well). I fixed the one in my V-Max with them for less than 3$.

 

I have the haynes manual with the diagram. I'm good at replacing electrical components not so good at diagnosing them. And the manual didn't say anything about diagnosing the diode block.

 

here's a quote from my boss to help you with your diagnosis:

"you see, every electrical component has, inside of it, magical black smoke. Once the smoke is released, it will never work again".

"like a bee"

"yes, exactly like a bee; once it smokes, its dead".

 

And once that happens you need a magician and his flute...(electrician and his fluke [multimeter brand]. I seriously thought someone told me that once...it was loud and he just told me about the magic blue smoke.

 

To test rectifiers with the diode check mode of a meter, you measure one way, and then with the leads reversed. The meter should show voltage drop of the device.

With the red lead on the anode and the black lead on the cathode, the diode should be forward-biased and should read a forward voltage drop between about .2 and .7 volts.

Reversing the leads (black on anode, red on cathode) should reverse-bias the diode and should show open, out of range, max, etc.

If you see the same value both ways (usually really low or really high/open) the diode is bad.

 

Well I tested the diode block

Between the White and White/Green I get closed one way and 510 the other way (figuring this means a .510 voltage drop?)
Between the Green and blue white I got open both ways

so I figured lets pull the coating off this thing and have a look and here is what I found




So should I go for the 3A or the 1A replacements

 

Nice Mav, thanx for the pic! that will help a lot of people I think, if ever the diode block becomes an issue for them.

Always good to have inside pics of enclosed electronics

 

Correct on the .51V voltage drop. That sounds like a pretty normal reading.

Based on what I see there, I'd go for a 3A rectifier.

Next question is whether something is shorted in your safety circuit....

 

hopefully I can test the relays and switches tomorrow and see if I can pinpoint a source.

If I don't see anything I can always toss in a new rectifier and see if the system toasts it.

 

Those old diodes are prone to breaking lust like the pic shows. I've had it happen in my V-Max and XJ diode blocks. Just solder in a new one and go ahead and replace the other one while you are at it. Put it back in the original rubber housing with some black silicone and no one will ever know its been worked on.
I used the 3A in both mine, they are bigger but will fit. You will have to drill the circuit board to get the wire leads to go in. A 1A will go in with no drilling.

 

hopefully that is it. and thanks for the heads up on the diodes

 

The problem is that a broken rectifier won't smoke. A shorted one might. If the broken one first failed to a short for some reason, then broke under the current load from the short, then you might have an explanation that's not based on any problems outside the diode block. Doesn't seem that likely to me, though.

 

Well got my diodes today it appears that I have something wrong with the neutral switch. It shows that I am always in neutral. I unhooked the wire from the bottom of the switch and everything worked fine. I plugged it back in and the diode started smoking.

 

Maverick you do know the diodes have to be installed a certain way right? The neutral switch is a ground its either a no or nc switch I am not sure but its not the problem because its a ground either way. Starter circuit relay checked yet?

 

[quote="SQLGuyThe problem is that a broken rectifier won't smoke. A shorted one might. If the broken one first failed to a short for some reason, then broke under the current load from the short, then you might have an explanation that's not based on any problems outside the diode block. Doesn't seem that likely to me, though.[/quote]

A breaking diode will smoke, not necessarily from excessiv load or a short. Since these diods are old and brittle the connection in there is weak causing heat buildup then smoke and finally breaking in half. I'm not saying that is definatly his problem just a strong possibility. I have seen them get hot enough to melt the rubber casing before the diode breakes just because they are old and weak.

 

yes I have the diode in the correct way. I didn't check the rest of the system as I noticed the neutral switch wasn't working first thing and unhooking it solved the problem.

I am going to be away from the bike for a bit so further diagnosis will have to wait.