Mercury cdm modules dies ?!?!

[Anders67]

Hi there.

Have 1996 120XR engine, later CDM ingnition model. Same CDM it seems on 3,4,6 cylinder engines.

New red stator. Original
New trigger Original
New recitifer. CDI

Put 4 new CDI CDM modules on for about two month ago. First one died, then another died on low rpm. , mow a third stone dead.


Is it something that can kill these modules that i?m not thinking of?. Ore are they known to be tricky??.

Only thing i can see more in the papers are that the kill-switch shall not go over 2 volt. and it does not ( 0,3 switch of, 1,3-1,5 switch on).


Someone that know anyting ???.



Regards from Sweden

 

[schematic]

Re: Mercury cdm modules dies ?!?!

Check all engine grounds. Check the ground circuit for the modules. Make sure they are all clean and tight.

 

[Texasmark]

Re: Mercury cdm modules dies ?!?!

Check all engine grounds. Check the ground circuit for the modules. Make sure they are all clean and tight.

Good idea. Some wiring harnesses have separate ground wire with lug for CDM ground which attaches to the screw that mounts the CDM to a mounting plate (some engines). That's OK fine but what about the plate ground? Find it, either a separate black wire going to the block, or just the mounting screws to the block for the plate and pull the screws and clean all that up too.

Real strange that they all went like that. If it's ground it's going to be a common ground, not an individual module ground so the plate is suspect. The CDMs could have come from a bad production lot....it happens. Where did you get them? Were they new and unused?

Mark

 

[Anders67]

Re: Mercury cdm modules dies ?!?!

Good idea. Some wiring harnesses have separate ground wire with lug for CDM ground which attaches to the screw that mounts the CDM to a mounting plate (some engines). That's OK fine but what about the plate ground? Find it, either a separate black wire going to the block, or just the mounting screws to the block for the plate and pull the screws and clean all that up too.

Real strange that they all went like that. If it's ground it's going to be a common ground, not an individual module ground so the plate is suspect. The CDMs could have come from a bad production lot....it happens. Where did you get them? Were they new and unused?

Mark

Hi.


I had the same thought when i went through this Wes Crawen nightmare of engine electric on this unit.


I have all negative on one screw on mine engine. Sitting in the plate the CDM mounted on.


So when i changed the stator/trigger/reticif./4 CDM 2 month ago. I run a new negative cable from that ground screw (there all grounding in the plate is done from trigger, stator, CDM) to the engine block, just to be shure.

I also cut of the ground lines from CDM harness in the end that it is bolted and soldered on new screw-shoe ( 2 negative lines on 4 cylinder).

I also mesured from ground screw/ other end of harness, to contact on harness to the 4 CDM units , so resistance was 100%.


Yes the 4 CDI/CDM units was brand new.


Weird??.


Try to look through the grounding again.


Thanks for the help.


Anders

 

[schematic]

Re: Mercury cdm modules dies ?!?!

I also have heard that some of the failures of these modules have been attributed to circuit board cracks. Heat is a factor. Be sure you have good cooling.

 

[Texasmark]

Re: Mercury cdm modules dies ?!?!

I also have heard that some of the failures of these modules have been attributed to circuit board cracks. Heat is a factor. Be sure you have good cooling.

Interesting, with a long service record in pulsed technology, I thought I would help my CDM's have a long life by installing thermal grease between the unit and the ground plate only to find out that the CDM has no metal plate requiring heat sinking to a sink; rather it is epoxy potted and as such doesn't give a flip to which it is connected because any sinking material was trying to sink heat from epoxy/plastic, rather than aluminum which is an absolute joke......45 years in the same type electronics business.

This tells me that the components are sized adequately to tolerate the rpms of todays engines.

Mark

 

[Texasmark]

Re: Mercury cdm modules dies ?!?!

I also have heard that some of the failures of these modules have been attributed to circuit board cracks. Heat is a factor. Be sure you have good cooling.

Circuit board cracks from where? The CDMs are epoxy encapsulated and a circuit board crack is a joke, an absolute joke. We are not talking about a 30 year old GE or similar mfgr. printed wiring board TV. The potting of these units unify them into a solid integral unit and you aren't going to have any circuit board cracks.

Mark

 

[schematic]

Re: Mercury cdm modules dies ?!?!

Why so angry Texasmark.

Circuit board cracks are all too common. I have cut apart MANY CDI units and have observed mostly cracked solder joints as the failures.
The potting material in some electronics does have heat sink qualities.
Some CDM modules have a service bulletin pertaining to the larger size engines. The same CDM is used on smaller engines and yet no bulletin exists. Off course Merc won't tell us why. These modules seem to fail more so on the larger engines, but an odd one fails on smaller as well.

I know there was a bad batch or two originally made. I should crack an old one open and see what failed. I just don't have the time....

 

[Anders67]

Re: Mercury cdm modules dies ?!?!

Hi.


Last day. Mesured the negative again from CDM-cable to ground. All 4 100% resistance.


Also run a cable to negative ground ( same as battery ground on engine).



!?!?!!?.Strange

 

[Texasmark]

Re: Mercury cdm modules dies ?!?!

Why so angry Texasmark.

Circuit board cracks are all too common. I have cut apart MANY CDI units and have observed mostly cracked solder joints as the failures.
The potting material in some electronics does have heat sink qualities.
Some CDM modules have a service bulletin pertaining to the larger size engines. The same CDM is used on smaller engines and yet no bulletin exists. Off course Merc won't tell us why. These modules seem to fail more so on the larger engines, but an odd one fails on smaller as well.

I know there was a bad batch or two originally made. I should crack an old one open and see what failed. I just don't have the time....

Not angry just stating my opinion. Last CDI I cut apart was back in the '70's and noted that the resistors had no tolerance band meaning that they were +/- 20% tolerance; very sloppy considering what some resistors are rated for critical applications. Just an observation that the trigger circuits are not critical at all.

Don't know how you removed the potting but that could have damaged the board/solder joints, but for you to have gone into one it had to be a failed unit in the first place so......you are more versed than I.

On Thermally conductive epoxy, yes there is, but you need a lot of metal flakes in it to get any kind of conduction and that wouldn't do well with an electronic circuit with the voltages used, and is no way near as efficient as an alum plate.

Really, a 6000 rpm outboard with a CDI for each cylinder is only firing 100 times a second and for pulsed electronic circuits that is loafing big time. So, as I said, a heat sink is probably not necessary. We used to run 10,000 times a second.....pulses per second (pps). That you had to keep cool.

Mark

 

[Anders67]

Re: Mercury cdm modules dies ?!?!

Well i sent a e-mail to CDI one-two weeks ago.

See if they replies.


Not yet !!

 

[schematic]

well...8 years later I had time to cut one apart. This is the circuit board from a Merc CDM.