Tach Repair

Joined
Aug 21, 2014
Messages
17
I have an old Autoguide 870 tach that went bad. Actually, it hasn't worked since I bought the boat. I started to troubleshoot it and went through the rectifier and what-not, then decided to take the tach off and take a look. Most of the posts say to just replace them, but it seems like it would be such a simple process to repair it. The only problem is that I can't see what the part is that burned out. I have attached a couple of pictures of the part. The yellow wire, which is actually the grey wire coming from the rectifier feeds directly into this part where I drew the arrows. Anybody have any idea what this piece is?
 

Attachments

  • photo209177.jpg
    photo209177.jpg
    100.6 KB · Views: 0
  • photo209178.jpg
    photo209178.jpg
    91.4 KB · Views: 0
Joined
Aug 21, 2014
Messages
17
No Title

Actually, it's an Airguide, not an Autoguide. Also, it doesn't look like my pictures posted so I'll try again...
 

Attachments

  • photo209177.jpg
    photo209177.jpg
    100.6 KB · Views: 0
Last edited:

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
Both of your topics have been merged into the original in Electrical. We suggest not starting duplicate topics in other forums. If your aren't getting replies it may be because no one knows or you haven't given enough time.

Repair is only a simple process when you know what the faulty part is and if that is the only cause of the malfunctioning tach. Other components may be bad as well.

Did you fix the charging problem with the motor? If not, you may blow this tach if you get it repaired or a replacement tach.
 
Joined
Aug 21, 2014
Messages
17
Thank you for the feedback. I was hoping that, by posting in both forums, the topic would reach a greater amount of people. I understand the issue though.
Yes, the charging system has been repaired. My question is actually specifically concerning the tach, however. If anyone has knowledge of their internal components, I would greatly appreciate it.
 

Star

Chief Petty Officer
Joined
Sep 21, 2010
Messages
481
That looks like a choke and it has to be tuned or selected for the circuit. Buy a new tach they are cheap for the most part.
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
It looks like the choke(Inductor) is sill there.
The missing part that is now smoke and char, was probably a protection Diode or a Fine wire used as a fuse.



Ohm across the inductor, is will likely measure less than 100 ohms. If more than a 1000 is is a goner also.
If you can get a clearer picture of BOTH sides of the board, it may be possible to reverse engineer it.

This damage is not a fault in the Tach. Something big and external tried to get in there.
If you replace the tach, the new one may smoke just as fast unless you isolate the problem first.
 
Joined
Aug 21, 2014
Messages
17
Sounds like we're on the right track. Unfortunately I'm out of town and can't get a picture of the back of the board. I have replaced the stator and rectifier so whatever fried it should be fixed. Heck, I've even replaced the tach but that's not the point. If I could find someone with one of these old Airguides I could just take a peek inside...
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
Old is the operative word.
That is definitely an "Old School" circuit in there. There is not even a Transistor!
I haven't seen that technology since the 1970's.

Smoked Tach2.jpg

Photo-Shopping the second Photo reveals what looks like the end cap of a low wattage resistor.
As a wild guess I would try 100 ohms. Anything much larger would not have smoked.
The resistor likely saved the inductor.
If the Tach reads too low try a 47 ohms. If too high 220.
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
I think the burned component looks like a capacitor. See the foil-looking winding. But we are all guessing.
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
I think the burned component looks like a capacitor. See the foil-looking winding. But we are all guessing.

I had considered that also.
The part was very small, so if a capacitor it would have been a non-electrolytic in the pF range and could withstand a lot of voltage.
If it was a low value resistor of less than 1/4 watt, it would have been much easier to smoke.

Also it appears that this Tach is a two wire device. No Power lead.
The movement is powered by the pulses from the ignition. Not very accurate, but about as simple as you can get.
A resistor in the input lead to limit the current makes more sense to me than a capacitor.

Troubleshooting from a Thousand miles away makes almost everything a guess.
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
Patagonia Pete;
Are you in or from Patagonia? (See Instructions in Signature below.)
Or are you associated with the Clothier?
 

NYBo

Admiral
Joined
Oct 23, 2008
Messages
7,107
Patagonia Pete;
Are you in or from Patagonia? (See Instructions in Signature below.)
Our locations aren't showing up in the avatar area like they did before the "upgrade." That's why I added mine to my signature.;)
 
Top