Alternator "tridiode?"

[Yarisduder]

My electric system dummy light came on the other day, so I figured it was the battery since I was told it is weak. So replaced the battery, and they tell me that the "tridiode" on the alternator which "sends the signal to the dash light" is faulty. The symptom it causes is that the electric light comes on when the car starts and goes off shortly afterward, but the system still charges fine. They say to fix it I'd need a new alternator, but since it's charging it's a waste of money to do that.

So my questions:
1 - Is this "tridiode" even a real thing?
2 - Can just the "tridiode" be replaced?
3 - Or is the real problem a corroded contact?

Thanks.

[CTScott]

Check this post out:

http://www.yarisworld.com/forums/showpost.php?p=502632&postcount=3

[Yarisduder]

Darn I missed that. Thanks!

[Sir A.Y. Atoyot]

My electric system dummy light came on the other day, so I figured it was the battery since I was told it is weak. So replaced the battery, and they tell me that the "tridiode" on the alternator which "sends the signal to the dash light" is faulty. The symptom it causes is that the electric light comes on when the car starts and goes off shortly afterward, but the system still charges fine. They say to fix it I'd need a new alternator, but since it's charging it's a waste of money to do that.

So my questions:
1 - Is this "tridiode" even a real thing?
2 - Can just the "tridiode" be replaced?
3 - Or is the real problem a corroded contact?

Thanks.
It's usually called a "diode trio." It supplies power to the regulator. It can be replaced on most alternators that have them. Sometimes they are integrated with the main rectifier assembly and sometimes they are a separate piece.

[CTScott]

It's usually called a "diode trio." It supplies power to the regulator. It can be replaced on most alternators that have them. Sometimes they are integrated with the main rectifier assembly and sometimes they are a separate piece.

On the Yaris, it's integrated into the voltage regulator assembly.

[Yarisduder]

He probably called it tridiode because he's French.

CT - Do you think cleaning the contacts as per your alternator break down post, or should I replace the voltage regulator assembly?

Also, do you happen to remember what size fittings I would need to replace them with stainless steel the way you did?

[CTScott]

He probably called it tridiode because he's French.

CT - Do you think cleaning the contacts as per your alternator break down post, or should I replace the voltage regulator assembly?

Also, do you happen to remember what size fittings I would need to replace them with stainless steel the way you did?

For what's required to disassemble it, I'd probably pickup a regulator before tearing into it. Cleaning the contacts and preserving them is a good idea if it hasn't failed yet, but might not help if it already has. Unfortunately, I don't recall the screw sizes. I brought one of each type with me when I went to the HW store to pickup the stainless ones (they were all metric though).

[Sir A.Y. Atoyot]

On the Yaris, it's integrated into the voltage regulator assembly.

Sorry, not to quibble, but an examination of the schematic doesn't show any diode trio component, inside or outside the regulator. Apparently, there is no diode trio present in this design.

On an alternator that does have this component, one end of each of a trio of diodes is connected to the phase windings of the stator, while the other ends are tied together and attached to the regulator. Compare, for example, the ubiquitous Delco 10si alternator, which has a diode trio as a separate component.

[Yarisduder]

So there is no diode trio... so that can't be the problem?

I'm going to try cleaning the external contacts first.

[Sir A.Y. Atoyot]

So there is no diode trio... so that can't be the problem?

I'm going to try cleaning the external contacts first.

Good plan. Make sure that there's plenty of travel left on the brushes. Have a good look at the stator windings and make sure there is no burnt or discolored appearance. If you can, check the diodes with an ohmmeter.

[CTScott]

The drawing of the internals of the alternator does not actually show a diode trio, but an equivalent function circuit is implemented within the regulator assembly. The purpose of the diode trio is to stabilize the alternator output at low RPMs. Your mechanic is working from past experience of why the charge indicator light comes on to have stated that he believed that the diode trio is bad.

Based on the the TSB for the 07, the frequency that the issue has been experienced by people on here with 07s, and your Yaris's symptom which match said TSB, I would most suspect the voltage regulator assembly being the issue. But, if you are going to disassemble it to diagnose it, it makes sense to check everything as mentioned above while you are in there.

[Yarisduder]

I just got around to fixing this. Here's a photo of the faulty part for anyone who's interested.

37209

37210

[CTScott]

I would call that a bit corroded. Did you have a tough time getting some of the screws out?

[Sir A.Y. Atoyot]

So, is the original problem solved?

[Yarisduder]

The bolts came off with no trouble, I was surprised because of how much corrosion was everywhere.

Since I ended up swapping out the entire alternator I can't say whether cleaning the corrosion off would fix the problem or not. Maybe when I'm bored I'll try hooking it up to an electric motor and measure the voltage to see what happens. It may take a couple months though.