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Bad PMDs Anyone? I know, the horse is dead already!!!?

btsayles

btsayles

Diesel Proficient
Messages
56
Reaction score
25
Location
Wisconsin Rapids
Hi, everyone.

I've been away for a couple of years obtaining a mechanical engineering degree and working full time, which didn't leave much time for fun things (as in zero). Well, that's all over with now, and I have time to play. I have learned tons of stuff from this forum over the years, and I appreciate it a great deal. Thank you all. I have done a search for people trying to repair the PMDs on the forum and didn't readily find anything. If I just missed it, tell me and I'll stop.

I've been lucky with PMDs over the years, and have taken all of the recommendations of having a spare in the truck to heart. My '95 6.5l shut off at the intersection outside of a store, and started up upon cranking. I immediately pulled into the first lot I came across (50 ft) where I shifted (automatic) into neutral. Upon neutral the engine ran away for 2 seconds and died again. Prior symptoms were a miss from time to time, but I know that can be from all kinds of things. I have my PMD remote mounted on a heat sync, and this last PMD has been alive for 5-7 years.

I am not concerned with the cost of a lifetime warranty on these, but since I had a bad one, I figured I would replace the transistors and see if that would fix it. I watched a ytbe video on some guys hacking their PMD with a small rotary tool and was curious about how they didn't hack up their circuit board the transistor was soldered to. Like a dope, knowing it was going to be nearly impossible to cut through the black, solid, opaque potting without damaging the circuit board, I tried to drill the transistor pins down through the board. It worked, but like crap and was a arduous process. I saw where I had damaged the CB in other locations as well. Oh well, I enjoyed myself. Destroying things is fun at times.

I got to thinking, every video I have seen of people trying to replace these transistors has ended the same way, nothing; there is never a, it worked like a champ with a running truck. That should be the first clue, right? If someone was really proud of their work, they would show the last clip of the video of a revved up turbo whistle.

I have a FUBAR PMD to practice on now. I grabbed the other transistor with a pair of C-man robo-grips (which I haven't used in like 15 years) and rocked and pulled on the transistor until it withdrew from the PMD. Trust me, this was not easy, but with a little patience, both pins slid out of the PMD with the transistor. Since there is nothing above the transistor pins on the PMD circuit board (CB), with no pin debris in the pin hole in the potting and CB, I used the pin holes as drill guides. With the PMD cover removed I drilled right up through the potting. Now I had guide holes to get me right back to the CB. I took a chamfer in a drill and followed the hole back down a touch at a time until I reached the CB pin soldiering location. This action is precision work, but very doable with the guide hole created.

Naturally, I'm not going to install good transistors into a part I know is junk. I'm sure after reading this, I'm sure some of you are going to try to replace some transistors.

The reason I went through this long explanation is because I am trying to beg for a couple of PMD to verify this actually works on. I'm not trying to make any money on this; I am just trying to give back to the great people of this forum who have helped me out of a few jams in the past. Once I verify the results, I will post a "how to" with clear pictures, instructions (including the parts and what the G means (contains no lead)), who that does not matter, and a running truck with the actual repaired PMD, covers off, to you, this forum.

I hope to not get hate mail or death threats because of this. Hope you all are having a great day. Please send me a PM if you have some dead PMDs I can toy with. I'd be happy to send a paypal gift for shipping. Thanks.
 
It would be nice if there could be a kit so a person could just build their own, sort of like the DIY Autotune EFI control boxes.
I soldered one of those together and it worked great.
I think with all of the black goo gone that the PMD would cool much better and last a very long time, then, if a component did burn out, it could redily be replaced.
 
Simple AK.. if we don't burn them up then they can't sell them..lol... I kept wondering why nobody has built one with a fan cooling system built right into it.. similar to what a computer has on the back..
 
It isn’t just overall heat. You could put an elaborate liquid cooled set up on them. It will still go. The bulletproof pmd is like the fountain of youth. From day 1 everyone wanted the perfect one, but it isn’t out there. A wazoo version could be made, but is anyone willing to put $5000 into one?
Way more affordable and less hassle to just buy 2 lifetime warranty units and 2 heatsinks.
 
Okay guys, I finally had a chance to play with some PMDs. The first one I repaired was a 2 beer job. The second without pictures was 10 minutes (could be 2 beers if you so choose). Both worked upon plugging into the truck in the block below. Both did not work prior to. This repair replaces the transistors under the little black keyhole looking covers on the bottom of the PMD. The beauty of this repair is, the next time you have a failed transistor, you only need to de-solder the two transistor leads from the PMD to remove and solder the new ones in. You will also be able to tell which one it is because the leads extend through the other side of the PMD so you can check which one has failed with an Ohmmeter. If you attempt this repair, I assume no responsibility for any injuries associated with your attempt. You are attempting this repair at your own risk. If you accept those terms, please continue. Here goes fellas.

1) Remove the two keyhole shaped covers from covering the transistors on the bottom of the PMD. Even a little light side pressure from a pen is sufficient to pop them free.
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2) Remove the cover from the top side of the PMD. It is the part that says Stanadyne on it. One of the PMDs, the cover popped off with very little effort. The other took a little more coercion. A pair of small screwdrivers or a spudger set work marvelously.5697156972

3) Remove the four 1/4" nuts securing the transistors.

4) I used an old pair of C-man robo-grips but any pliers/channel locks that can grab the head of the transistor will work. Grab the transistor, and carefully pull it out while rocking the transistor. It is difficult to withdraw the transistor because you are pulling the pin out of the potting (black plastic filler) and out of the soldered connection on the circuit board at the same time. If you are careful, you will not break the transistor leads. It may take a few minutes to get the pins worked out, but they all came out in one piece for me.

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5) With a #60 drill (Ø0.040"), using the open transistor pin holes as drill guides (seen in the figure below), drill all the way through the potting. These drilled holes will be your guide to chamfer back to the board from the potting side. This way you have access to the board where the pins come through the board to solder the transistors to the board.

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6) I used a 60° chamfer tool that came to a sharp point to chamfer down to the circuit board. Any degree of chamfer will work fine; it just needs to have a sharp point so it will follow the Ø0.040" holes previously drilled in step 5). Chamfer down a little at a time until you see a little solder ring forming at the very base of the hole. Do not chamfer any farther or you will destroy your part. As you can see in the figure below, depending on the depth of potting in each location, your chamfer diameter will vary to get to the board depth.
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7) Once you have chamfered down to the board in all 4 holes, install your transistor heat syncs or replace the heat syncs with the heat sync paste (can be purchased on Ama^&* , Eb^&, New E99 your preference). Due to the offest pin location on the transistors, they and the heat syncs can only be installed one way, so don't worry about polarity. Insert the new transistors into the PMD. The transistor leads will extend through the potting slightly. You could clip them off, but they are nice to have to solder the leads to the board and de-solder down the road if need be. Install the 1/4" drive hex-nuts and tighten (use your judgement on a #10 thread for torque should be about 20 inlbs. you're not holding the truck together).

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Ran out of space, the rest of the procedure will follow. (Thanks for your patience)
 
8) Apply a bit of flux to each pin to help the heat transfer into the transistor lead from the soldering iron and solder the transistor leads to the circuit board. Just a tiny ball of solder on the tip of the iron is sufficient to solder the connection and will travel down the lead to the board on its own very quickly.

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9) Once all of your transistor leads are soldered, give them a wiggle to see if they soldered to the board. If they wiggle, just apply a little move heat to the transistor terminal to reflow the solder. Now is a good time to hook up the PMD to your truck and test it. Make sure you have a fuel scheduling resistor in the PMD, otherwise the PMD will get very hot very fast.

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10) If your PMD does not make the truck run, then there was something else wrong with your truck or the PMD. I have only repaired two of these and both were because of the transistors which I forgot to tell you what they are and where to get them. If the transistors were not what was wrong with your PMD, de-solder the transistor leads and save them for the next one, or throw the whole thing away because the transistors are only like $4 a piece.

11) Clean the flux from around the transistor leads and apply a dab of silicone adhesive around the leads. I do not bother putting the cover back on because it does nothing to protect from moisture and will only need to be removed to repair in the future. I have seen a video where a guy super-glues the cover back on. If you want a heck of a time getting your cover off later, go ahead and try that.
The next time you have to change a transistor, pull out your multi meter and ohm out the transistors to see which one has a resistance which is not 20±~1 ohm and replace just the bad transistor. You will be able to remove the silicone, de-solder the transistor leads and remove it easily because you left the leads easily exposed.

A special thank you goes out to AK Diesel Driver for donating a dead PMD for this experimentation which proved easily successful.

In case I cannot edit the previous post I will put the transistor information here.

MJ15004 Power Amplifier Transistors. The MJ15004G is the same transistor; the G just means it is lead free. It doesn't matter. You can save a little money a piece if you buy them in bulk, but I would lose them by the next time I need them anyhow, so I only buy two at a time. I bought mine from E-b@7, but any electronics website or source will do.

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Sorry I didn't feel like editing a video or uploading it, but you can see the alternator cooling fan is obviously spinning. I know anyone could pop the covers off of the transistors and hook up a new PMD to show a truck running.

Put your covers transistor covers back on your PMD and put it in the golve box for that emergency roadside repair fellas. Good luck, but it's pretty easy. I hope the people who sell these PMDs don't get too pissed!

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This is awesome. Thanks for putting details here.

I got the feeling that the PMD seller from China is doing what you are doing.
May be with better tooling so that they can put it back together better.
Although, they may not have access to the truck to test it so that is why the quality is questionable.
We have the truck, so we can test it right away.
 
N8in8tor,
The pictures side by side I just dropped in and drag the corners to where you want them. I didn't really have to do anything special I noticed.

JMJNet,
I don't think there is a better equipment for replacing the transistors. Soldering the pins to the board is as good as the OEM. If you want the cover back on, just put a dot of super glue on each of the posts that go into the potting and it will hold it in there fine. I just put a dab of silicone over each solder joint for corrosion protection. One can simply pluck that silicone off the next time a transistor goes bad and troubleshoot which one is bad. This repair makes it very easy to replace the transistors in the future. Barring a resistor burning up on the CB itself, these PMDs should be reusable for longer than the truck survives.
 
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