Troller dual power pack

[sd75i]

  The 0-20 stayed a constant 20 no matter what position throttle was in

[sd75i]

  I tried a little bit to pry that board away from case but i think it will damage the board.  i thought maybe the metal prongs could have been pushed through the orange caps but i dont think they are.

[mmagliaro]

  The 0-20 stayed a constant 20 no matter what position throttle was in

Oh!    That's good.  That means you are getting +voltage to that side's throttle circuit.
Constant full voltage on the C is what I would expect.

The 0,0,0 on the other transistor, however, is bad, as is the fact that you are getting nothing on the base
of either one.  I think we are dealing with multiple failures.

But in the meantime, trace all the wires from both transformers and try to describe where they are all going.
(sure wish I had a schematic for that thing).

[mmagliaro]

Just to make sure...
The C should be the center lead on those transistors.  You're absolutely sure you are getting 0 volts on
the C lead on the left-side transistor?

That would be really bad.   That would imply that either that side's glass tube overload device is bad,
or that side's transformer is bad.

Did you ever unsolder one lead on each of those glass tubes and check that they are zero ohms across their leads?

[peteski]

  Ok, i used black lead on - D.C. Access and red on B, C, E.    Left side 0, 0, 0.  Right side 0, 20(0-full), 0.  All 0 readings were throttle 0-full.

Just to be 100% sure, when you measured the DC accessory output with your multimeter, it was reading a positive, not negative (no minus sign in front of the number) voltage, correct? Then you left the negative (black) lead on the DC accessory where it was before,  and you then took red lead and started measuring th BCE voltages, correct?

[peteski]

Oh!    That's good.  That means you are getting +voltage to that side's throttle circuit.
Constant full voltage on the C is what I would expect.

The 0,0,0 on the other transistor, however, is bad, as is the fact that you are getting nothing on the base
of either one.  I think we are dealing with multiple failures.

But in the meantime, trace all the wires from both transformers and try to describe where they are all going.
(sure wish I had a schematic for that thing).

Max, since there are 2 separate power transformers we speculated earlier that the DC accessory output is coming from one of the transformers. Sine we suspect that each throttle is isolated then we really should concentrate on troubleshooting the throttle where we get the non-zero readings from the transistor. We can then try to work on the other throttle later.

This thread should really be moved to the electronics forum (that fourm is not only for DCC problems) 

[Carolina Northern]

My guess is that's it's the wrong ground for the other throttle.
Trying to wrap m head around the two transformers - both identical to the one in mine. Best guess is throttle and AC acc on one, throttle and DC acc on the other.

Since he sees the 20 volts on one side, that's probably what his meter can see of the rectified AC coming off the bridge. Should see something very similar on the two outside legs of the pot.

[Doug G.]

I would get those power trannies out of there and test them since they are the most likely things to have failed in a device like this. They carry the load. While they are out, check the supply voltages to them to eliminate the possibility of a short bringing the voltage down (although that should normally trip the breakers). If voltages all check OK, put new trannies in there and all should be well. If voltages are not OK, other components need to be tested (I know, that's obvious )

I agree that a schematic would make things a lot easier.

Doug

[peteski]

I would get those power trannies out of there and test them since they are the most likely things to have failed in a device like this. They carry the load. While they are out, check the supply voltages to them to eliminate the possibility of a short bringing the voltage down (although that should normally trip the breakers). If voltages all check OK, put new trannies in there and all should be well. If voltages are not OK, other components need to be tested (I know, that's obvious )

I agree that a schematic would make things a lot easier.

Doug

Doug, but we still don't know exactly what we're checking!    Also, in a typical transistorized throttle the power transistor is in series with the positive supply voltage and the positive track output. Any sort of a short on the transistor should not cause any load on the power supply, or cause the breaker to trip.

[sd75i]

  I have not yet unsoldered the bulb thingers.  What are trannies?

[Doug G.]

I know Pete but I have always started out checking the high current devices in a power/amplification circuit because they are the ones that will fail with an overload. SD75i, trannies are transistors. Sorry, I have called them that for many years. Actually, there are several things with the nickname "tranny". Transistors, transmissions, transmitters, etc.

I just have always gotten those output/power transistors out of the way first because they are the most likely to be bad with a no output situation. The same is true of HiFi amplifiers of which I have considerable experience too. If the output transistors are OK, then look elsewhere. Otherwise, you can make measurements all day long for nothing if those outputs are bad.

Doug

[sd75i]

 
Just to be 100% sure, when you measured the DC accessory output with your multimeter, it was reading a positive, not negative (no minus sign in front of the number) voltage, correct? Then you left the negative (black) lead on the DC accessory where it was before,  and you then took red lead and started measuring th BCE voltages, correct?


That is correct.  I retested and same results!

[sd75i]

   So should I unsolder the B,C,E thing?  If so, how do I test it?  I couldn't find that part when I tried to look up the number I had online.

[mmagliaro]

I am not at all convinced that unsoldering the power transistor (the "BCE thing") will allow the voltages to that transistor
to come up, but it can't hurt  to test for this, and it's not hard to do.

1. On the transistor where you got a good +20v on the Collector (C), unsolder the 3 wires to the transistor.  Make sure you
mark or make notes as to which one goes to which terminal before you unsolder them.

2. Now, repeat the test on the 3 wires (with no transistor attached to them).  Just to see if the voltage to the Base wire rises and falls
with the throttle position now.  If it does, then indeed, it would seem that the transistor is causing a problem and should be replaced
before we can move on.  If not, then there is surely something shot in the earlier stages of that throttle that has to be fixed.
There are probably other small transistors on that board and one of them might have burned up.

Don't worry about the other side, where you got  all 0,0,0.  I think Peteski is right on that one.  Let's try to fix one side at a time.

Don't worry about trying to actually test the transistor.  You can do some sanity "dead or alive" tests with an ohmmeter, but
it would be more foolproof to see if you are getting voltage at the Base first.

Finally, YES, unsolder on lead of those thermal glass overload devices and measure the resistance across them.
If it is not zero ohms (or darn close to it), that fundamental problem has to be fixed before anything else can be tested.

[Doug G.]

The easiest thing to determine what is going on the quickest IS to test the two output/power transistors. This is almost standard practice in devices like this. Checking voltages is useless if these components have failed.

To check a bipolar transistor:

1. Place either lead of the ohmmeter (on the ohms setting if the meter doesn't have a diode check setting, most do these days) on the base (B) of the transistor.

2. Touch the other lead to both the collector (C) and emitter (E), in turn, and note whether you get a reading or not. They both should or should not have a reading.

3. Now reverse the leads and put the other lead on the base and touch the lead that was on the base to the collector and emitter, in turn, and you should get a reading both times if you didn't in the first test and you should not get a reading if you did in the first test.

4. If those tests were OK, touch the two leads between the collector and emitter both ways and you should NOT get any reading.

The transistor is good if these tests are OK.

A transistor is kind of like two diodes connected at the base and you are checking both diodes to be sure current flows only in one direction in both diodes and also to be sure there's no short between the two diodes.

If either or both transistors are bad, you most likely have found the cause of no output. If they are both good, obviously now is the time to check other things like voltages.

Doug