I was half way through a 100 mile trip recently when the generator on my 27 Tourer stopped charging. It was showing no charge but plenty of discharge with the lights on. The generator has worked fine for a long time.
On top of the generator is a rectangular box that looks like a regulator. It's unmarked except the battery terminal is marked BAT.
If I put an analog meter on the output of both the generator and the cutout I get 0v at fast idle.
There is an extra wire that comes out of the brush plate cover that goes to a toggle switch under the dash. That goes into a homemade regulator. The BAT terminal of the box on the generator also goes into the homemade reg.
It runs 12v and my father would have built the regulator probably 30 years ago.
I realise I need to replace all the wiring and put a fun projects regulator on, but that is a big job for another day. Any ideas on where to start looking for the fault?
Check your brushes.
Probably brought out the field wire and thus controlled the field current from his regulator. Rewiring the third brush to an external control makes the generator essentially into a 2 brush generator. The LM741CN is an operational amplifier that probably was used to compare the battery voltage to a reference to thus give more or less field current to control the output. The switch under the dash probably turned off all power to the regulator to prevent battery discharge when the thing was shut off.
See if you can find any sort of diagram or notes your dad might have made since the wiring is complicated enough that it is very likely he made a diagram of it. As we get older we keep better notes since we can't remember what goes where even though we may have been the inventor of the thing.
You Might want to by pass the out board regulator for a test along with checking your brushes. If the generator now has output, Check the output transistor connections on Your Dad's regulator, its the black plastic transistor with three leads and red,black & green wires soldered to it with the transistor tab bolted through a insulator with white thermal compound going to the heat sink.
In the picture the wire solder connections at the black transistor look suspect solder can crystalize over time and fail being subjected to heat. You can resolder the connections and that may solve the problem or depending which connection failed it may have knocked out the transistor. The solder Your dad used was probably Rosen core 60/40 lead solder which is good stuff, now days they use environmental friendly lead free solder and it fails early and often, The RSTL / odometer digital readout failed on My wife's 2000 Buick,Display went black, the problem was the Lead Free solder had failed and the series dropping resistors fell off the instrument cluster circuit board, replaced 4 resistors for a dollar or two at radio shack resoldered with 60/40 solder and back in business, High Dollar repair at the Dealer.
Thank you for the suggestions. For a quick test I disconnected the wires labelled D in and D out from the homemade reg and shorted them. Showing about 1v at the generator output.
I'm sure I've seen a regulator diagram somewhere, not sure where it is now or whether it is for this one or not. Will have a look for it.
The regulator also has a potentiometer that I assume controls the output.
F is the field winding wire
L is a dash light
Din is wired to the generator
Dout goes to what I think is a capacitor then to the ammeter or ignition switch
The brushes look OK. While I had the cover off I noticed that extra wire is rubbed through the insulation. Tested it with that no longer shorted but no change to the output.
Would running with that wire shorted do any damage?
It would be impossible for even the most experienced of us to have any idea of what went where and exactly what each wire goes to. I think you need to find out where this design came from and get a schematic for it or else you would likely save time and money to put the whole thing back to at least a stock setup so you can drive it.