CDI failure?

CDI rebuild attempt...

So I just discovered my '86 700 isn't firing on cylinder number four... Checked for spark and there's nothing. So I tested coil number 2 and had spark, so plugged in coil 4 in the coil 2 position and still no spark, so I figure bad coil/wire. But then I put coil 2 in for coil 4 and still no spark, so I'm thinking it must be the CDI box. Checked for continuity between the connectors at the box and the coil terminals, all checked out and no short to ground in the signal wire. Did all resistance checks for the wiring listed in the manual, everything checked out (except for coil 4 of course).

So I ordered a coil/wire on eBay to replace the faulty one, but I wanted to see if anyone has any other ideas before I spring for a CDI box. I may crack it open and just see if there's an obviously burnt cap or something...

TIA

 

Yep, i discovered that my assumption that a CDI would fail totally and not on just one cylinder WAS WRONG !

 

Is there anyone local you could hit up to hook up their running CDI to test?
I bought an extra one or two so I could test or replace if one gets fried.

 

I'm working on procuring one from ebay... I don't know anyone else with a 2nd gen, I figure I'll just give fixing mine a shot in the meantime, the circuit board sure doesn't want to come out of the box though...

 

Well opening the CDI box isn't the most fun you could have, only one end opens and the board is *supposed* to slide out, but I broke a big chunk of PCB off trying to get it out. I dremeled the bottom of the case off and pulled it out that way, only to discover that the part of the board that broke was all scorched due to a blown up transistor. So that explains the not firing in cyl 4. Going to patch it up with wire and some new transistors if I can locate some, here's some pics...

The broken board


Charring


The Culprit

 

Uh oh, can't see the pics at work but some of those IC's unless they were generic IC's might be impossible to source.
Sounds like your Regulator might have sent a spike or a capacitor may have exploded, I think there were a few electrolytic caps in mine when I peeked inside my CDI unit.

 

That's brilliant !

I'm staying tuned to this joint ! Brave to plunge in there, you'll be a real VFR HERO if you can fix it !!!!

(if you're missing an idle jet, look on your workbench.)

 

That's just a screwdriver bit I believe... And the fried component is just one of the ignition transistors. They're pretty commonly used in Japanese ignitions it seems, I ordered a couple on eBay but I'm going to try to source some locally, I'm kinda impatient. Thankfully the part of the PCB that broke only had a couple of traces in it so repairing that part should be some easy soldering.

 

Nice pictures!!! I will stay tuned in for the progress!!!

 

Well it ain't pretty, but it works! We'll see how these transistors hold up, I think I may need to modify the heatsink a bit. But I've got spark on cylinder 4 now, hopefully I'll get the replacement ignition coil tomorrow and I'll be up and running on all four for the first time!

Had to replace both transistors, big one is a beefy NTE2317, small one is 2SD7899 I believe which is really similar to the OEM one, just handles more voltage. I have two OEM 2SD1071s on the way just in case, these are the ones I could buy locally.


Ghetto PCB patch work.


I think I should still try to pick up a CDI for a spare, if anyone has one... (especially one that doesn't have a broken PCB...)

 

Your an electrical gawd - What do you use for a soldering station? Do you like those butane mobile rigs?

Nice write up, wish I had 1/4 of your lectrical smarts :wink:

 

Like I said before for transistors to go up in smoke it usually points to power supply problems and the places I would look to for that is the R/R and if the CDI has its own voltage regulator.
If you do not address these problems you might end up having these issues come up again, hopefully you don't.

 

The R/R was just replaced with a brand new unit, so it should be good still. The old one going bad may have done it though, I kinda think that the bad ignition coil caused it, I'd imagine it's much like having an ignition trigger but not actually fire, not very good for it.

 

Well I just threw everything back together with the new ignition coil and double checked for spark on all cylinders, and WOW. Scared the crap out of myself, I feel like the bike must have run like a moped before, now I know why ripping the throttle on this thing was supposed to be scary, I feel like the front wheel wants to come up. =D

Feels literally at least twice as fast, hopefully the fuel economy doubles as well (was getting about 120 miles to a tank...)

Thanks for the help!

Oh, and regarding the other stuff in the electrical system, I think the RR was unrelated, I think it just had a bad coil. I remember first time I went to denver I popped about 8 fuses but after I made it a little over half way there it stopped, I never figured out why it was doing that. My guess is the CDI firing into a dead coil caused some sort of a voltage spike that blew the fuses, and by continually replacing them (didn't have much of a choice) I eventually burn out the transistor.

 

If it is not too much trouble you might want to check those diodes near those transistors, if those transistors took a whallop I imagine those diodes took some bad voltage spikes also.

 

Great work, and a strong-running VFR is your reward !

 

Well It's still working fine, I do have a spare unit on the way though.

 

How about some instructions for getting the circuit board out of the box ????

 

He lives in CO, maybe he is double-secret-james-bond-007-agent working for NORAD?

Thats why there is surpression of the black-box, (is that term even politically correct anymore?)