GML Enterprises

[mmagliaro]

Your measurements from rectifier "+" to ground of 48 mean it's NOT a voltage doubler and there is really 48v on there.

Since you opened up the one that worked, did you happen to read those voltages on the same pins?  That would be a really good thing to know.  48 is kinda crazy, but if the working one has 48v on there, then that's the way he designed it.

[peteski]

Your measurements from rectifier "+" to ground of 48 mean it's NOT a voltage doubler and there is really 48v on there.

Since you opened up the one that worked, did you happen to read those voltages on the same pins?  That would be a really good thing to know.  48 is kinda crazy, but if the working one has 48v on there, then that's the way he designed it.

If it is a standard rectifier circuit with a filter cap on the DC side, and the power is supplied from accessory (AC) terminals of a standard power pack, how can that result in 48V DC?

[mmagliaro]

If it is a standard rectifier circuit with a filter cap on the DC side, and the power is supplied from accessory (AC) terminals of a standard power pack, how can that result in 48V DC?

I have no idea.

If it were a voltage doubler, we'd have -24 from the "-" to ground, and he has zero.  Hmmmm maybe that plate
he touched the "-" meter probe to is not ground...

Peavine: 
How about this...
Maybe that plate you touched the negative meter probe to is not ground.
Are you able to look at those two large electrolytic capacitors, and see if the  "+" lead from one of them goes to the "-" lead of the other?   (Usually the cans on those have a "-" where the negative lead is).

If the + from one cap does go to the - of the other cap, try touching the "-" probe from your meter THERE.
And touch the "+" probe from your meter to the "+" and then "-" pins on the rectifier and see what you get.
You may see +24 and -24 after all.

--------
And realize, if you can measure this, and you can do the same measurement in the working one you bought,
all we know is that the basic power supply is probably okay.  Sure wish there was a schematic to look at what goes where.  It will be very hard to diagnose without that.

[Ed Kapuscinski]

I got one for free just walking into Harbor Freight with a coupon some years back.

I've got one of those! Worth every penny I spent on it... lol.

[Peavine]

I did what you said and got exactly what you said I would, +23 volts, and -23 volts.

I then repeated that for the new one and got the same results.

Agree that without a schematic...

[mmagliaro]

I did what you said and got exactly what you said I would, +23 volts, and -23 volts.

I then repeated that for the new one and got the same results.

Agree that without a schematic...

Okay.  So, we kind-a figured, but now we know that the rectifier and capacitors are okay.

Well, I see a few options here, none of them easy.
If you are able to, draw a schematic by following all the traces on that board, and then share it with the group.
If it was mine and I was really determined, that's probably what I'd do.  It would be so much faster to know where to
look for a problem by seeing the schematic.
(tall order, I know)

Option 2:
Turn on the bad and the good throttle, same settings.
Leave pulse, momentum, and any other special features OFF.
Make sure there is some load on the throttle.  Just hook a light bulb across the outputs.

Check the voltages on the two OUTER leads of the speed control pot (in the hand unit, right?) and make sure they agree between the two throttles.  If they don't, trace them back through the unit, taking periodic readings until you figure out where the voltage goes wrong between the two throttles.  But if those are okay...

Then, start from the CENTER lead of the speed control pot (I assume it is in the hand-held unit) and trace it everywhere it goes, reading voltages on the good and bad throttles.  (put negative lead on that connection between the two caps, and probe with the positive lead). 
 
My hope is that you'll go through a diode, op amp or transistor somewhere and suddenly see a big difference between the two throttles.  Realize that your path may take you to a device like that 5-pin "thing", and then you'll need to test all the voltages on all the pins of that device, and follow all 5 of those.

That's about all I've got at this point, short of unsoldering batches of components and testing each one, starting with transistors, diodes, and capacitors. 

I have a really bad feeling about longevity of a throttle like this that is completely undocumented, with parts that have their numbers ground off.   Unless a family friend of the designer could find a way to tactfully ask his family if they could look around for drawings or schematics, and ask them to publish same since all support for this thing is gone and the customers are now left hanging.