Hi all, new member here. It was suggested I ask my question here so here it goes. My 17yr old son had restored a 1975 dt125 with the dynastart system that he could never get to charge, it starts but no charge. Fast forward 3 yrs and hes away at school and would love to get it charging for a Christmas present.
I been through everything, cleanless of connections, brushes, everything seems to ohm out ok. I think its just the connections on the insulator block on the dynamo.
Although most are clear enough due to the colour coding and pics I have found but its the right side,white wire, that I need confirmation on. Are the positive brushes, white wire, large gauge wire from magnets and small gauge wire from magnets all to be connected together?
I've looked in the manual and on google with no luck, can someone take a picture of there connections, draw me a picture of how its connected, snapshot of a diagram, anything to help would be appreciated.

 

Capt Dave posted this pic a few years ago...  I added notes. Best way to troubleshoot is use the procedure in the manuals.  All the theory and step-by-step checks are there.  

  

thanks MarkT, I was looking for confirmation on the A terminal (white) wether the positive brushes, large gauge wire from the coils and small gauge wire from the coils poking through the window from behind the a terminal were all connected together.

I seriously doubt it.  There are two systems with a common armature.  Starter and generator. 

Have you followed the service manual troubleshooting procedure completely from start to finish in order?  Best to start there. 

Yes there is a bunch of wires on the far right - all connected together - including the white one
to solve this quandary before Christmas focus on voltage regulator searches 
 

thanks for that picture,that helps. problem is there's not much voltage coming directly off the dynamo.

So I've been pouring over the net looking for how a starter/dynamo works just so I can try to understand this thing better, haven't found anything that I can understand easy. From doing all the tests it seems to me things look ok but still am wondering about the smaller gauge wires coming from the field windings? they have continuity but I'm not sure there suppose to, can someone confirm this?
the ohms checks seem close and visually the dynamo looks mint. If I test voltage at the dynamo while running,I get between 5/7 volts
Also looking at the connections diagram in the manual for the 125c isn't super clear to me, if the wires were color coded it would sure be helpful.

It's hard to help when you say things like "generator puts out 5-7 volts when running".  So is that when performing the "dynamo test" at 1,800 rpm as described in the manual?

 

If you go through the steps and post the results for each one, you'll find the problem...  at least I've never had following the manual steps and checks in order and as described fail to identify a generator problem.

Here's some tips though:

There is a color AT1 wiring diagram in the Tech Library.  Generator wiring is the same as your bike

The earlier manuals have better test and troubleshooting sections in my opinion...  so again, try following the AT1 generator/starter section in the service manual from the Tech Library.

There is a 1969 Yamaha Shop Guide in the Tech library...  you have to read carefully to make sure you're looking at the correct type of system but the manual describes the general theory and operation of the generator better than anything else.

Happy troubleshooting!  Hope you find it quickly and fix it easily.

Forgot to say that in the AT1 manual, after the dynamo tests they go over the ignition system...  past that, they get into the Voltage regulator. 

You can skip the ignition stuff and go to the Voltage Regulator section. 

thank you, I will check it out