1982 seca 750 not charging

hi folks,

So I’ve been trying to figure out why this bike of mine isn’t charging. I’ve read quite a few posts and information threads and believe everything is pretty good except the resistance test on the rotor is reading 7.0 ohms instead of the spec of 4.0. The brushes are well within their spec and I cleaned up all connections and the rotor face. Is it possible I need to swap the rotor? Any advise on doing so? I have a spare engine I could swap parts on if needed.

 

It could be your voltage regulator on the left side behind the side cover . How old is your battery? Is it fully charged ?, if it is a lead acid battery are all the cells fully serviced with distilled water? Be aware the charging system really does not put out much of a charge at idle , above 2000 rpm you should have 13 to 14 volts test with a volt meter at battery terminals . One other item to check are your grounds points . Cheers

 

I had the same issue on my 1982 750 Seca. I checked the battery, the brushes and the regulator. It was the regulator that was faulty. The PO had put a very cheap pattern regulator on - one from amazon costing £18! I replaced it with a decent pattern one from M & P and it's been fine ever since.

 

I think I’m going to order up a new voltage regulator, I can get one from ricks for about $120. I guess it’s worth a try. The battery seems to be fine. It was reading 11.9 after a week since I charged it with my battery charger last weekend. Also probably started the bike 10-15 times since the charge. I had the bike running well past 2500rpm when I checked for a charge on the battery terminals with no increase past 11.9

I swapped the brushes with the set from my extra motor and I’m still not within spec on a resistance test on the green and brown wires. The reading was about the same as the old brushes (~7 ohms) Which is why I thought maybe it’s actually the rotor giving me problems.

 

The either your regulator is dead......my first bet,————

or your alternator/stator isn’t producing charge.

you might be lucky and simply have a wire off somewhere........

 

you are not reading the brushes resistance you are reading rotor resistance. it is just easier to read through the brush wires.

 

Hmm, interesting point. I guess I assumed the resistance reading was from the brushes contacting the rotor.

So it kinda sounds like I might need to swap out the rotor. I’ll look into doing that. Might need to get creative to figure out a homemade ‘rotor puller’

I do have a voltage regulator ordered as a backup. In case the rotor swap doesn’t do the trick. Although everything tested right when I was doing this ‘rectifier test’ as per the Haynes manual.

 

I’d swap regulator first... simple things first— unplug/plug vs. tear into things....

 

I have some good oem regulators rotors and windings before you go nuts spending 120. And check the ac output direct from stator when bike is running without regulator plugged in. Between any 2 white wires

 

I got my new voltage regulator/rectifier and installed it. Still no charging is happening at any rpm. I did a AC voltage test on the three white wires while the bike was running. Got a reading of .4v at idle and about 1.0-1.2v at 2500-3000 rpm. Which makes me think that everything up until that point is working fine. Any further thoughts? Something I should try before attempting mild insurance fraud?

 

I just tried the voltage regulator test from the Haynes manual. It says it should read under 1.8v with the ignition on and raise to 9-11v once started. However I’m reading 11v with only the ignition on. What might cause that to happen?

 

What happens when the bike is running

 

Are you getting 11 volts on both multimeters? My bike was not charging when l got it and it was because the brown and green wires to the brushes were connected to the wrong connector block in the wiring harness. I changed them over and that fixed it.

 

So if you put your meter on 2 of the white wires(red probe on one and black on another) you only get 1-2 volts that’s bad should see 50-60 volts AC.

 

There is an error in the Haynes manual and some of the Yamaha Service manuals. The V2 voltage is checking the brown wire, which is switched battery voltage. The V1 voltage is checking the green wire, which is the regulator control line. The attached document has it right in that the green wire (regulator control) should be checked for the 1.8V. The brown wire should be battery voltage (or slightly lower) with the bike not running, and increase as the motor is revved.

 

Well maybe that’s where I’ll start. I wasn’t sure how much output it would have but I am nowhere close to 50+ volts AC. I picked up a better multimeter and re-checked the resistance on the components. The white wires to the stator were fine. However the check on the green and brown wires to the brushes were out of spec. I got a reading of 11 ohms. So I’ll try to swap out the rotor and see if that does the trick.

 

Would testing the resistance between the two rotor tracks directly with the multimeter work as well? I am reading 4.7 ohms when I do that. Maybe it’s a wire or connection giving me trouble? Just a thought before I pull out the rotor.

 

The spec is 4.0 +/- 10% so you are just barely high, probably not an issue - if you touch your leads together you can subtract that reading from the 4.7 ohms.

Through the brushes you would like to see a slightly better reading, but the 11 ohms is pretty common. You can try cleaning the field coil slip rings with a hard eraser and wipe down with contact cleaner or isopropyl alcohol to see if you can lower it.

I was hoping you would have redone the V1 V2 test. You can't produce a voltage in the stator unless you create a magnetic field in the field coil. To do that you need the green wire to be pulled toward ground. The lower it goes the stronger the magnetic field and consequently the greater the output from the stator. With the bike not running the regulator should pull this low to max the magnetic field. You can verify the presence of the magnetic field by placing a thin feeler gauge near the AC Generator cover and when the key is turned on the magnetic field will pull the feeler gauge toward the cover.

Be sure to check them to chassis also, as there are several places where they can be pinched - they should be open to chassis.

 

yes .
you read through brushes first then at rotor if reading through brushes is out of spec.
your looking for 4 ohms . touch your probes together see what you get for a reading if anything shows you would subtract from the test reading.
you may need to cleen the rotor copper tracks

 

Okay, I believe I've got the brushes and rotor cleaned up to just out of spec. Like 6.0 ohms. I also have new brushes arriving sometime this week from ebay that might be able to get that right on spec. I cleaned the rotor with an eraser and isopropyl. Is it ill advised to use steal wool or fine grit sandpaper on the rotor?

I now believe that this V1 V2 test is exposing my problem. I installed a new regulator that i bought off amazon, that may be my first problem but it had fast shipping up to canada. So with the new regulator/rectifier connected my V1 and V2 both read nearly full voltage with the key turned on and while started. No change on both reading of 10.9v ish no matter what. So I guess that voltage regulator is toast.

I tried reconnecting the old regulator/rectifier and I had a reading of 1.2v on V2 with just the key turned on which is under 1.8v like the manual says. However the voltage never climbed up to 9-11v after starting like it was suppose to. It just stayed at 1.2v. The V1 reading was 10.9 before and after starting the engine. So i guess that one is toast as well and that was probably my original problem.

I guess I should mention that I brought up the RPM's on each test with no change to the voltage readings.

I will seek out another regulator/rectifier and hopefully it's what is giving me my grief. Any leads on where I can get a decent one that might arrive before this riding season slips through my fingers?

 

The voltage at the green wire (V2) indicates that the regulator portion of the Rect/Reg is doing just what it should. V2 is the control voltage and is adjusted according to the sense voltage (V1). V2 will not rise unless V1 rises toward the desired charge voltage, which requires a complete working system and a fully charged battery. With a differential of nearly 10V between V1 and V2 you should have close to 2 amps of current flowing through the field coil producing a magnetic field. When the motor is started the rotating magnetic field should produce an AC voltage in the stator, which is then rectified to convert to DC and applied to the battery through the main fuse.


Check the magnetic field strength just to be sure using the thin feeler gauge in close proximity to the AC Generator cover. The feeler gauge should be pulled toward the cover when the key is turned on.


Once a magnetic field is verified I would recheck the stator resistance and verify the stator has no shorts to ground. If OK restart the bike and check the AC output of the stator between phases, which should be around 18 volts at idle and increase rapidly as the motor is revved (note testing with stator connector unplugged).


I don’t see where the diodes were checked in the original regulator. If you have a healthy AC voltage at the stator output it is possible the diodes have failed in the Rect/Reg, which needs to thought of as two separate parts – the control section (V1/V2), and the AC to DC section – the diodes.

 

crocus cloth is ok to use to clean rotor clean rotor after to remove any loose crud

crocus cloth does not shed its grit like sand paper

 

A hard art eraser works too.

 

Okay, So I spent some time on my bike today. Rotor is cleaned up and the resistance test on the green and brown wire is within spec. As well as the resistance test on the three white wires

I did the diode test as per the link Rooster53 sent me. The brand new rect/reg I bought failed on a few diodes so that whole unit is going in the trash. However, the original rect/reg checked out fine.

I checked the white stator wires for ground faults and everything seemed fine with them, well once I disconnected the rect/reg.

I didn't notice a well defined magnetic pull against the alternator housing but I thought I felt a little pull. I then proceeded to start the bike and check for AC voltage between the three white wires. On all combinations of the wires I was reading about the same voltage: ~13vAC at idle and ~50vAC at higher rpm. I noticed you said "note testing with the stator connector unplugged" but my bike wont start with that connector unplugged

It seems like everything is functioning like it should except I'm still not getting any DC charge on the battery. Very frustrating. I have a friend that has a seca 650 that I believe uses the same rect/reg. I hoping I can borrow his just to check if it will charge with his installed. If that works I'll just order another Rect/reg and hope its not a dud like the last one.

Any other suggestions? I really appreciate all the help you folks have been giving me and all the info i've collected from some of the other forum posts. Its real cool to have a group of knowledgeable and friendly people to bounce ideas around with.

 

It should start fine however the ATARI will not initialize and the headlight will not illuminate. Does it crank and not start? History? Was the charging system working before and suddenly quit? Has there been any wiring mods on the bike?

Those are some good numbers "if" the 3 pin stator connector was unplugged. If the connector is mated the output voltage is restricted by the load of the battery and would never get near 50 VAC unless:

The diodes are open effectively disconnecting the stator output from the battery.

Or,

The large red wire that exits the regulator is not connected in the harness and tied to the battery positive through the main fuse or the regulator ground is not connected and it is not tied to chassis / battery ground.