93 SPX MPEM

[Maxpax]

I have a 93 SPX and a 93 GTS. Many years ago, I replaced the mpem on the SPX but kept the old one. I am a retired electronics tech and now have time to experiment with troubleshooting the old mpem. The problem is the potting compound that seals the electronics. Has anyone here figured out how to remove that potting stuff ? I have tried acetone and different carb cleaners (some that have xylene) with little success. Picking and cutting the stuff away isn't much fun. I have no real need to fix this as both of my pwc run fine, I am just curious what shorted in my original mpem and if I could actually repair it. I have 40+ years electronic troubleshooting and multiple solder certifications. I just need to see the components to build a basic schematic. Thanks for interest and maybe a reply or two. Max

 

[mikidymac]

Pick it out.

 

[Maxpax]

Pick it out.

That is what I have been doing ... usually on a rainy day. I would like to get it done faster but ...

 

[burtshaver2021]

From what I understand it’s usually a diode. I have picked away at the potting and can see the diode now mostly, if you have the same MPEM I could send you a picture of it so that you know the location of t he diode and save you a 10 or 20 hours of picking

 

[Maxpax]

a pic of mine. I haven't done anything with this for a good while and dug it out this am. Thanks for the reply.

 

[Maxpax]

From what I understand it’s usually a diode. I have picked away at the potting and can see the diode now mostly, if you have the same MPEM I could send you a picture of it so that you know the location of t he diode and save you a 10 or 20 hours of picking

That appears to be the case on my mpem. I dug out the stuff around the area above (top of the pcb) the 2 large pads (solder side of the pcb) and saw what looks like a Motorola diode. I desoldered one lead of the diode and the short went away on the board and the diode tests shorted. I will dig more stuff out around the diode and remove it and try to find a replacement. I am glad I posted this and got a good lead to the problem part. Thanks.

 

[burtshaver2021]

That appears to be the case on my mpem. I dug out the stuff around the area above (top of the pcb) the 2 large pads (solder side of the pcb) and saw what looks like a Motorola diode. I desoldered one lead of the diode and the short went away on the board and the diode tests shorted. I will dig more stuff out around the diode and remove it and try to find a replacement. I am glad I posted this and got a good lead to the problem part. Thanks.

I have a bag of diodes that I purchased for this, I would be interested to see which ones you use

 

[Maxpax]

Well, I dug down deep and got the diode out. It is a MR2535, a transient voltage suppressor. It protects electronic equipment from voltage spikes and can (and often does) short and blows a fuse. If it is connected to the start solenoid circuit ( or other circuit with a coil or transformer) it will keep voltage spikes from damaging other circuits. With the mpem, it might help in some situations but when it shorts the mpem has to be replaced. Not sure what else it could protect. I searched the net for replacement part numbers and found the original part (MR2535L) is available on Ebay. A substitute part BZW50-22 is available from a few electronics suppliers. I will probably buy one (or two) and repair my mpem. I'll test it and if it works, I'll have a spare.

 

[burtshaver2021]

Amazon.ca
These are the ones I purchased, I see they are no longer available, on Amazon anyways