Mercury Switchboxes

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talbot

Recruit
Joined
Apr 4, 2004
Messages
5
Hi All,<br /><br />Has anyone ever had any luck repairing their switchbox. If anyone has any pointers on what is failing in these boxes that would be good. Has anyone had any luck unpotting them.<br /><br />I have a 1996 25HP Merc (Electronic advance). My engine is hard to start, once started will run hard but after about 10-20min of running the engine dies. The engine will idle but die as soon as a load is put on it. If you let it cool down for 20min you can run along a bit longer. I have a manual and have tested all the ignition components which give the correct values, but as my fault is intermittent its hard to pinpoint it.<br /><br />It seems like the main fault is the switchbox from reading the forums. <br /><br />Any help appreciated
 
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remmer38

Seaman
Joined
Feb 23, 2004
Messages
72
Re: Mercury Switchboxes

The switchbox wiring I believe is pretty much embedded in the plastic. Its one large complex resistor. Piece of mind on the water is worth the money. You cant walk back so easy. Try Ebay also.
 
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remmer38

Seaman
Joined
Feb 23, 2004
Messages
72
Re: Mercury Switchboxes

I didnt read the other part. Long night at work. Compress test first. Is there spark on plugs and is it strong? Im not real familar with newer motors but they all gotta have the same ingrediants. If spark is strong, look to fuel problems. Fuel pump problem? Pull the tube from the fuel pump that goes to the carb(s) . Crank the motor and see if fuel flys out of it. if it does then that part of the full system can be pretty much rueled out. Hopefully a reed valve didnt come apart. Good luck and post more of an explantion after these tips. I love this site as I am a commercial fisherman and live in such luxury. Hard work but look where I get to work. Call me crazy. Ive looked at so many posts and can always learn more. <br />Capt. Emmer
 
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fishhead24

Cadet
Joined
Apr 4, 2004
Messages
19
Re: Mercury Switchboxes

Most likely it is the switchbox. It cant be repaired! I've seen it alot of times . Once it gets hot it starts to break down, especially under a load.
 
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KCLOST

Commander
Joined
Jun 22, 2002
Messages
2,095
Re: Mercury Switchboxes

Check the spark at idle... Then, run the engine until it dies, <br />check the spark on all cylinders right after,<br />If you loose spark on the cylinders, it's probably the box...<br /><br />It's a lot of money to replace so confirm before you spend...<br />Let us know...
 
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talbot

Recruit
Joined
Apr 4, 2004
Messages
5
Re: Mercury Switchboxes

Thanks all.<br /><br />It is the switchbox. Thanks REMMER38 for the tips. I should have said in my post, but i had moved past the mechanical checks as they were okay. I was lucky enough to be able to test my boat with a spare 2nd hand unit. Ran like a dream. Now I just need to cough up the dough for a new one. <br /><br />If any one is interested, and because i cant help myself, i have pulled my ignition unit apart and removed all the potting. Mine does still run but breaks down when it gets hot. If anyone wants any info on whats inside let me know.<br /><br />A little tip, dont catch your crab pot ropes in the Prop. I had one get in behind the prop and the force of the rope winding in stripped the nylon prop nut almost clean off. Almost lost the prop but limped home with a feed of Crabs for easter.
 
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remmer38

Seaman
Joined
Feb 23, 2004
Messages
72
Re: Mercury Switchboxes

Anytime my friend. I hit an obstruction while a lady friend and I were "camping" on the boat I was moving us out of an area experiencing high wind. It loosed the bushing in the prop hub and left it to free spin under any power. Im sure we were a sight after a 12 foot v hull came along and pulled our twenty footer in to dock. Glad you made it safely. Catch a fish.
 
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dogsdad

Lieutenant
Joined
Aug 8, 2003
Messages
1,293
Re: Mercury Switchboxes

Talbot, I would be most interested in knowing what's in that switchbox. I replaced one last fall and tried to get into the defective one, but ended up just tossing it. But I'm one of those guys who likes to know what's in electronic boxes!<br /><br />-dd-
 
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talbot

Recruit
Joined
Apr 4, 2004
Messages
5
Re: Mercury Switchboxes

No problems,<br /><br />I am a bit like you, i just had to know what was in it. Removing it wasnt that hard. If you cut carefully between the casing and the potting you can remove the module out as a complete block being carefull to cut around the charge capacitor at on end. I found that turps tended to soften the potting and loosen the block in the housing. Once i had it out, i tried a few solvents but mainly just dug it out carefully. (if ayone has tried a betted solvent let me know)<br /><br />My unit was an electronic advance unit so at I was pleasantly surprised as most of the components can be identified apart from the advance circuit. It is a Hybrid PC board that stands off the main board. Basically everything else were standard components. The circuit does not differ much from the block diagrams in the manuals (Pulses from the Stator are rectified and charge a cap, Trigger cct fires the SCR's.) <br /><br />I havent removed the Hybrid PC board as yet but i would say it is not something we can buy off the shelf. I would say that this is where my fault is. If i had a no spark fault I probably would be able to fix it. If i get some more time i would like to try the unit on the motor and see if it fails again.<br /><br />Hope that helps
 
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dogsdad

Lieutenant
Joined
Aug 8, 2003
Messages
1,293
Re: Mercury Switchboxes

Talbot, thanks for the info. I take it that the SCRs in turn fire the coils. Is this correct?<br /><br />-dd-
 
LubeDude

LubeDude

Admiral
Joined
Oct 8, 2003
Messages
6,945
Re: Mercury Switchboxes

Talbot: Contact me at:<br /><br />Rays-shop1@juno.com<br /><br />I may have something for you!
 
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talbot

Recruit
Joined
Apr 4, 2004
Messages
5
Re: Mercury Switchboxes

Yes, Thats correct SCR's fire the coils. There is a primary trigger device and a main voltage SCR as well
 
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