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shokwave2
Samba Member
Joined: February 02, 2010
Posts: 264
Location: Wollongong, Australia
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 Posted: Sun Aug 18, 2013 2:10 am Post subject: Tacho jumpy at idle unless multimeter connected?!? |
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Just installed a VDO tachometer today and hooked up a multimeter to check the accuracy. It was spot on reading 850 at idle and spot on when reved. But when i removed the multimeter the tacho showed higher and jumping around at idle, anywhere from 1100-1500. All i did was attach the multimeter to - side of the coil and to a ground, and the tach works fine. Electrics are 12V, points, alternator, tacho is wired to the coil. Is this a grounding issue somewhere, with either the coil or tacho?
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longboard511
Samba Member
Joined: August 21, 2012
Posts: 133
Location: england
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| Posted: Sun Aug 18, 2013 2:25 am Post subject: |
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| im sure sometimes they need a diode fitted in line do a search on jumpy rev counter im sure you will find the info |
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shokwave2
Samba Member
Joined: February 02, 2010
Posts: 264
Location: Wollongong, Australia
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| Posted: Sun Aug 18, 2013 2:31 am Post subject: |
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Cheers, will do.
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Quokka42
Samba Member
Joined: December 02, 2010
Posts: 3117
Location: Melbourne, Australia
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| Posted: Sun Aug 18, 2013 2:36 am Post subject: |
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Yes, that can help. two diodes such as 1N4004 back to back should fix it. The reverse breakdown should be enough to smooth it, otherwise, buy a couple of Zeners of 15V or more and do the same.
If it is an electronic ignition, you can also try sticking a condensor across it.
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shokwave2
Samba Member
Joined: February 02, 2010
Posts: 264
Location: Wollongong, Australia
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| Posted: Sun Aug 18, 2013 3:25 am Post subject: |
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| Quokka42 wrote: |
| Yes, that can help. two diodes such as 1N4004 back to back should fix it. |
So i should install 2 diodes, not 1? I can't find 1N4005 on Jaycar's website, so would 2 x 1N4004's be equal?
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Eric Hodges
Samba Member
Joined: May 01, 2011
Posts: 95
Location: Simi
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| Posted: Sun Aug 18, 2013 12:26 pm Post subject: |
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Yup.
Or 1N4001, 1N914, ... any diode.
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Dale M.
Samba Member
Joined: April 12, 2006
Posts: 20798
Location: Just a tiny bit west of Yosemite Valley
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| Posted: Sun Aug 18, 2013 1:22 pm Post subject: |
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Radio Shack ..... Walk in, drop $1.98, walk out with diodes...
Dale
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gt1953
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Joined: May 08, 2002
Posts: 13947
Location: White Mountains Arizona
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| Posted: Sun Aug 18, 2013 6:59 pm Post subject: |
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Mine only needed the one diode, I have a small box of them. Any diode that can handle a couple of amps is fine.
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shokwave2
Samba Member
Joined: February 02, 2010
Posts: 264
Location: Wollongong, Australia
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| Posted: Sun Aug 18, 2013 11:58 pm Post subject: |
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Well got a pack of 4 diodes for $1, tried installing just one and it's done the trick. Thanks everyone. Although other guys have said their VDO tacho came with a diode included in the package. Mine didn't, oh well.
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