Guts of a PMD

[ak diesel driver]

So while I was waiting for the oil to drain on an air compressor I building up I decided it was as good a time as any to disassemble a PMD. There was actually a little more to it than I thought there would be. Fairly complicated circut board with chips. The resistors we all see are actually soldered to/thru the metal plate which must also be the circut pathway. The potting compound is what makes these so hard to disassemble without destroying things , it's hard as a rock which suprised me I thought it would be more like a soft hot glue compound. I'm starting to wonder if these things are voltage or ground sensitive. Makes me wonder if it shouldn't have an extra ground wire ran to it when it's remoted.

 

[Dieseldad97]

Cool. I'm thinking 175 bucks ain't to bad for one of these now.

 

[NVW]

So while I was waiting for the oil to drain on an air compressor I building up I decided it was as good a time as any to disassemble a PMD. There was actually a little more to it than I thought there would be. Fairly complicated circut board with chips. The resistors we all see are actually soldered to/thru the metal plate which must also be the circut pathway. The potting compound is what makes these so hard to disassemble without destroying things , it's hard as a rock which suprised me I thought it would be more like a soft hot glue compound. I'm starting to wonder if these things are voltage or ground sensitive. Makes me wonder if it shouldn't have an extra ground wire ran to it when it's remoted.

When I built my extension harness I used sheathed trailer wire. It had one extra wire so I ran a ground to the heat sink. I thought it couldn't hurt.

 

[bison]

AK,looks like you did a cleaner job than me. I didn't have much luck without breaking the circuit boards all up.

What actually beats me is why there are originally plastic covers on the resistors?.
If the resistors are the ones needing cooling the most,these covers plus the open area's surrounding them sure makes for poor heat transfer to the heatsink me thinks

 

[ak diesel driver]

the metal plate that everything attaches to is the heat transfer area me thinks. also I'm starting to think that the resistors aren't failing I think it's the electronics

 

[buddy]

the metal plate that everything attaches to is the heat transfer area me thinks. also I'm starting to think that the resistors aren't failing I think it's the electronics

Yeah, perhaps from zapping them with high powered jump chargers Those didnt exist so much when it was originally designed. Although I would expect there to be a Zener diode or something like that to shunt more than 15V to ground through a resistor perhaps. And if it does, then perhaps ensuring the heatsink itself is well grounded would be good, and a thermal transfer pad might not be a good idea, if it doesnt conduct electricity.

Thanks for the pics

 

[ak diesel driver]

that might explain the better service with the artic silver paste

 

[buddy]

I use arctic silver on all things that need a heatsink, hasnt failed on the intake yet in 3 years. I also have the IP/PMD ground on the heatsink, but another ground wire from there to the top of the IP, and grounded by touching the aluminum intake and bolts. I also never use jump starters, and have never jump started my truck at all in the 3 years.

 

[JMJNet]

Are those resistors or transistors?

Great pictures!!! Thanks.

 

[Turbine Doc]

Are those resistors or transistors?

Great pictures!!! Thanks.

Transistors

 

[3500GMC]

TO-3 metal can transistors. I didn't notice any heat sinking compound to the black colored block.. (internal heatsink?). Just a mica gasket or some sort?

Who only knows which small 50 cent component fails forcing us to buy another $200 PMD.

I dunno if this has been posted here but there is some techie type info about the PMD/FSD's on this site.. http://www.flashoffroad.com/Diesel/injectionpump/fsd.htm They're saying thermal cycling and just plain HEAT as the cause of failures.

I do agree that the automotive electrical system is a crappy harsh environment.

 

[Turbine Doc]

I dunno if this has been posted here but there is some techie type info about the PMD/FSD's on this site.. http://www.flashoffroad.com/Diesel/injectionpump/fsd.htm They're saying thermal cycling and just plain HEAT as the cause of failures.

I do agree that the automotive electrical system is a crappy harsh environment.

Some debate to my "lack of science" in testing method, but long ago I did this test http://www.thetruckstop.us/forum/sh...s-to-Ponder-quot-How-hot-does-it-get&p=140974 that convinced me heat fails were a component to some that have crapped out