MadScientistMatt UltimaDork
10/23/23 8:32 p.m.

Spin off of the Dart build thread; some wanted details on the time I cut a voltage regulator open and it was full of sand. This started when Greg (slantsix on this forum) had a few comments about getting new voltage regulators that failed shortly after installation. I decided to have a look for myself. I bought a MasterPro 2VR1, $32 from O'Reilly.

The black plastic sealing the unit is probably a two part urethane or a silicone based rubber, as it cuts easily with a knife.

Cutting deeply into the potting compound with a box cutter revealed a layer of sand underneath it.

6 Dodge Dart

Cross posted with my teardown thread on ForABodiesOnly for those not on FABO. Here, I will dissect an aftermarket replacement for a Chrysler voltage regulator and post my findings. This is a MasterPro 2VR1, $32 from O'Reilly.


The black plastic sealing the unit is probably a two part urethane, as it cuts easily with a knife.


Cutting deeply into the potting compound with a box cutter revealed a layer of sand underneath it.


After cutting around the entire perimeter, I was able to pry out the layer of urethane.

The layer peeled off in one piece.

There is a circuit board underneath, wired to the connector with bare strands of wire. The one on the right broke off since it was stuck in the potting compound. The other two did not reach up into the potting until almost at the point they tied into the connector.


The circuit board is a single layer surface mount design underneath a layer of conformal coating. I'm not sure exactly what material it is, but I suspect it's FR2 or another laminated paper substrate.

I examined the circuit more closely under a microscope.

The design closely resembles Chrysler's original circuit redone with surface mount parts.  However, Chrysler used a thermistor to adjust charging voltage to match the engine compartment temperature and taper off charging as the engine warmed up. The temperature sensing is conspicuously absent here; the circuit runs the same voltage regardless of temperature.

So, first, here's what they did well with this regulator.

The soldering work on the PCB itself is first-rate. I'm guessing it was run on an automated production line using solder paste and a reflow oven. It's not impossible to hand place components like this, but getting them placed that precisely isn't easy. And the solder joints are almost certainly not hand-soldered with an iron.

The circuit itself is a very simple design with not much to go wrong and not much that can kill it. The most likely things that could damage the circuit are water intrusion or an alternator field coil that draws more current than the power transistor can handle. Unfortunately, I could not find any markings on the power transistor, so I don't know what its maximum current is. Even though there aren't any discrete components for protecting it against voltage spikes, this circuit should be able to withstand spikes to 40 to 60 volts without any problem, possibly even higher.

And here are the areas of concern.

While the PCB soldering is done very well, the wire soldering is second-rate. While the joints look functional, their technician seems to subscribe to the idea of "The bigger the blob, the better the job." The conformal coating job was also done poorly, leaving many areas of the board uncovered.

I don't like the idea of a sand filled box. Sand filled electronics have valid applications where there's a concern about a box getting filled with explosive gas, such as natural gas pipeline stations, but that doesn't apply here. While this box didn't show any signs it would leak, if you made a mistake like leaving a big greasy fingerprint around the area where the urethane fills the box, it's game over. On the upside, it does make teardowns easier - perhaps their warranty department insisted on this. It's not an unacceptable way to build electronics, but I don't like it. I also wonder how (or if) they were able to keep the shop floor clean when they're pouring a lot of sand.

As noted before, there's no temperature compensation. It runs at a fixed voltage.

And then there's the issue of tolerances. The resistors are cheap 5% tolerance pieces. Zener diode voltage tolerances are also around 5% unless you spring for something special. Theoretically, you could stack the tolerances so the voltage is off by 15%. That is unlikely to happen in practice, but it is theoretically possible. Most of these are probably going to be within 5% of their target voltage.

Heat sinking isn't ideal, but this circuit doesn't put out a lot of heat, either.

I can post a more detailed look at how the circuit itself works if you're interested.

Mr_Asa GRM+ Memberand UltimaDork
10/23/23 8:38 p.m.
MadScientistMatt said:

I can post a more detailed look at how the circuit itself works if you're interested.


Shavarsh HalfDork
10/24/23 2:52 p.m.

Awesome breakdown

californiamilleghia UberDork
10/24/23 3:13 p.m.

Wow , thanks for the report , 

I wonder if anyone at O'Reileys etc  ever took one apart or even cared ?

Just makes you wonder what other parts are made like this !

Noddaz GRM+ Memberand PowerDork
10/24/23 3:21 p.m.

Thank you.  I am pretty sure the only reason for the sand was to give the part heft and to make it feel substantial.


WonkoTheSane GRM+ Memberand UltraDork
10/24/23 4:44 p.m.

Wow, great tear down!  Thanks for taking us along for the ride!

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