tach doesn't work & charging problem

[70johnson]

I hooked up my tach tonight that I used on a prev. motor. tach signal to grey wire. It wouldn't move. Hooked up meter to battery and had no increase in voltage while running. What is the link between no tach and no charge, stator or rectifier? Rectifier passed alt to + terminal test but not ground to alt terminal test. Stator yellow leads had continuity. I have used the search button but most of the strings were unfinished. I have an 84 inline 6 90HP Merc.

 

[WillyBWright]

Re: tach doesn't work & charging problem

Remove the leads from the rectifier. Check for continuity between the yellow leads. I don't know the spec, but if you have resistance the stator is probably okay. The rectifier would fry if the battery connections were ever loose or corroded, or if someone happened to connect the battery backwards even for a split second.<br /><br />Know who's the most likely to connect a battery backwards? Electricians. Go figure! To someone working with AC all the time, Black is Hot. So instinctively they connect the black to the positive.<br /><br />The tach signal comes from the stator. But if the rectifier is bad, no alternating takes place and there is no signal.

 

[Clams Canino]

Re: tach doesn't work & charging problem

Dollars to dognuts it's the rectifier. Part number 816770T. They seem to pop a diode if you so much as look at them the wrong way.<br /><br />Mercury gets about $38 for them. They are usually up on Ebay all the time, cheap. Search on:<br />"mercury outboard rectifier" or search on "816770T"<br /><br />Hint: When you put a new one on, make sure the battery is fairly well charged before you go out on the water and hammer it. A nearly dead battery looks like almost a dead short to the output of the rectifier, and can pop another one. <br /><br />Ask me how I know? <br /><br />-W

 

[70johnson]

Re: tach doesn't work & charging problem

Thank you both. I didn't know that if the rectifier is bad it would affect the tach. I will try to pick one up Friday and let the gang know.

 

[David R]

Re: tach doesn't work & charging problem

70Johnson<br /><br />I think the answer is hiding in your discription. It sounds like you have no connection to ground from the Stator. Your battery won't charge because of the open path in charging circuit. Likewise the tach has no Stator (pulses) to ground reference.<br /><br />I'm not sure where the wire is located, but your looking for a grounding lead to the block. Possibly broken at the terminal or just plain disconnected. It is possible that the lead at the stator end is opened, thats not good.<br /><br />Best<br /><br />David

 

[Clams Canino]

Re: tach doesn't work & charging problem

The stator on that model either grounds to the block via the stator frame OR via a black ground wire - this depending on which "A revision" of the stator is mounted.<br /><br />However, that ground is more for the red and blue ignition windings. The yellow charging winding has both ends equally ungrounded and just produces raw AC. The raw AC is fed to the legs of a full wave bridge rectifier. One side of the rectifier is grounded, the other side produces the POS DC voltage. <br /><br />The tach signal is picked off from one of the two yellow leads off the stator. If the rectifier is hosed, that signal can be ruined.<br /><br />-W<br /><br />

Originally posted by David R:<br />70Johnson<br /><br />I think the answer is hiding in your discription. It sounds like you have no connection to ground from the Stator. Your battery won't charge because of the open path in charging circuit. Likewise the tach has no Stator (pulses) to ground reference.<br /><br />I'm not sure where the wire is located, but your looking for a grounding lead to the block. Possibly broken at the terminal or just plain disconnected. It is possible that the lead at the stator end is opened, thats not good.<br /><br />Best<br /><br />David

 

[David R]

Re: tach doesn't work & charging problem

Clams Canino<br /><br />

However, that ground is more for the red and blue ignition windings. The yellow charging winding has both ends equally ungrounded and just produces raw AC. The raw AC is fed to the legs of a full wave bridge rectifier. One side of the rectifier is grounded, the other side produces the POS DC voltage. <br /><br />The tach signal is picked off from one of the two yellow leads off the stator. If the rectifier is hosed, that signal can be ruined.<br />

Didn't have a schematic with me, nor could I find one on line. I was thinking fullwave (two diode rectifier) as apposed to fullwave bridge rectifier. Interestingly most of the wiring diagrams in my Selco manual use pictured objects so it isn't explicit what the internal circuit of the stator or the recifier is.<br /><br />However, I stand corrected on what the true circuit is.<br /><br />Best<br /><br />David