TCI issues? Gonzo? what to do?

[jpdevol]

LOL: No "Hey Stupid..." from this old timer.... Very thorough progression ( & humorous) ending as the Manual does: replace TCI unit with known-good one. Keep us posted...


As an aside; Yamaha never saw fit to post spec resistance values for the igniter unit (may not be a reliable diagnostic excercise) but, for giggles, perhaps once a replacement TCI resolves the issue, you could perhaps take comparative readings and post here?

 

[jetmechmarty]

@DB90, did you manage to sort the no spark issue? I have a client's low mileage and very OE 1980 that ran a treat for weeks whilst in the shop waiting on chrome bits to arrive, and I rode it ≈10mil of a Friday and come the following Monday wouldn't rev beyond 1300ish RPM, loaded or otherwise. I've checked and found the following to be in working order or within spec:

-dynamic compression
-fuel jetting
-checked carb balance
-battery voltage
-disconnected the rectifier and ran it
-ran it off a car battery to insure it has the proper voltage
-measured the voltage directly at the TCI box replaced the coil with a new
-the voltage and grounds directly at the TCI connector (6-pin, btw) & other grounds in system
-magnet in rotor has what appears to be adequate magnetism
-fuel flow through the petcock
-to make certain ran it off a test tank with 93 & 100 octane to remove the possibility of fuel delivery issues
-clean the carb passages & jets
-reset float height & verified needle & seats function properly
-airflow into the airbox
-removed kill switch from ignitor circuit
-new spark plugs, 3 pairs of NGK just to be certain in recommended heat range and a step up and down, just to be certain
-Verified connections from pickup coil to TCI box
-verified connections from TCI to coil
-changed plug leads & caps(getting desperate)
-verified tightness on igniton coil & pickup coil fasteners
-removed pickup coil cover to eliminate potential grounding

I just bought an oscilloscope (which I feel like a chimp trying to land the space shuttle whilst using it) and've yet to hook it up to measure the pickup output whilst running at idle against the TCI output, and also as it increases in RPM. That'll be next unless one of the old timers here has a 'Hey, stupid...' to throw my way. I've been thorough, but am ostensibly human historically prone to err.
I found at least a few other threads on this forum where XS owners have had the 'it ran great [insert single-digit number of day] ago but now only idles' Covid variant, all with bikes running the electronic ignition system, but the threads all seemed to've petered out or went the, now closed, Pamco route. If I had a second known-good TCI box, I'd toss it in. I've ordered one but it has yet to arrive. Any links, insight, advice, or motivating insults are welcome. I'm verging on talking him into converting to points (ignition seppuku) or going with the match, petrol, whoompf! option.

I’ve had my bike for 40 years. I had one TCI failure and it happened within the last 5 years. The bike was easy to start and idled fine. When I tried to go, it would only limp at best. I sent the TCI for repair and it has been running great since. I don’t know if sharing this is any help, but here it is.

 

[british standard]

I’ve had my bike for 40 years. I had one TCI failure and it happened within the last 5 years. The bike was easy to start and idled fine. When I tried to go, it would only limp at best. I sent the TCI for repair and it has been running great since. I don’t know if sharing this is any help, but here it is.

I've even opened the unit. There were 4 diodes and a larger... transistor? that looked to've been replaced/re-soldered at some point. The rest of the solder joints look fine. I don't see evidence of cracking or poor soldering, no scorching or obviously knackered electro bits. Where'd you send you unit off to? Are they still in business?

 

[jetmechmarty]

Where'd you send you unit off to? Are they still in business?

I sent you a PM.

 

[Jan_P]

Why not take some measurement on the transistor .There are instructions online how to do it.
If it has fried there are typically a resistor also fried somewhere but a Radio / HiFi repair man can probably find it.