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Alternative to a bad tachometer filter?

noquacks

Jun 26, 2013
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People,

Have a 1987 Pontiac sunbird GT non turbo, and tachometer filter seems to have died. Finding a replacement is almost impossible. Is there any way to either bypass it or fix it? A picture of it is here:


I think it has to do with micro farads of a capacitor(?). Just a guess based on related readings. Post #4 on this site might help with an idea on how to make one:


Thanks, people.
 

kellys_eye

Jun 25, 2010
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Not much in there susceptible to normal failure. That said, all the parts are bog standard components, Can you measure the resistance between the two wires? Should read around 13,000 to 17,000 ohms (13k to 17k).

The capacitors are most likely to have failed but you cold knock up a replacement unit for a few dollars with components from Mouser etc.

Replies further down that thread also pint to solutions or tricks to try. Have you had a go?
 

noquacks

Jun 26, 2013
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Not much in there susceptible to normal failure. That said, all the parts are bog standard components, Can you measure the resistance between the two wires? Should read around 13,000 to 17,000 ohms (13k to 17k).

The capacitors are most likely to have failed but you cold knock up a replacement unit for a few dollars with components from Mouser etc.

Replies further down that thread also pint to solutions or tricks to try. Have you had a go?
Thanks, Kelly. That is a great way to start- by checking ohms! I will start there and let you know. I am open to try to make my own with parts, as you suggested.........Sound like fun.
 

ivak245

Jun 11, 2021
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You could use a suppressor (capacitor) that you find on the back of an alternator or mounted on the coil.
 

TCSC47

Mar 7, 2016
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For me the most likely cause of the problem could be a broken wire or corroded connection, so check that there is continuity between the tacho signal source and the tacho.
But certainly a simple circuit that is not safety critical and you could make yourself. The components are pennies.
 

Bluejets

Oct 5, 2014
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You could use a suppressor (capacitor) that you find on the back of an alternator or mounted on the coil.
Maybe not the correct frequency block.
From memory the alternator type are rather large, perhaps 3uF whereas ignition for radios are around 1uF or less.
Circuit above uses 2 x 8n2 probably ceramic type also.
 

noquacks

Jun 26, 2013
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Wow, thanks, people! I will follow up on these tips as soon as I get a chance- when I get home from work iot is already dark.......
 

noquacks

Jun 26, 2013
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Just checked for ohms and the meter shows no reading, meaning no resistance. I also clicked the meter at the ring/buzzer tone mode and got no tone. So now, I think we know it must be a bad filter, right? Options to make? What parts? Can I buy from Amazon?
Thanks, people.
 

kellys_eye

Jun 25, 2010
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Radio Shack would have been the usual go-to but try contacting radio hams locally who might either have the parts (it's standard stuff and I have dozens of the parts in my 'trash' store) or can direct you to a local parts supplier.

Failing that a small order to Mouser or similar would probably cost more for the postage than the parts! 2c per resistor, 20c per capacitor so 50c worth of parts! (and $10 for postage!)

Had you been local (UK based) I'd send you the stuff FOC.
 

noquacks

Jun 26, 2013
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Radio Shack would have been the usual go-to but try contacting radio hams locally who might either have the parts (it's standard stuff and I have dozens of the parts in my 'trash' store) or can direct you to a local parts supplier.

Failing that a small order to Mouser or similar would probably cost more for the postage than the parts! 2c per resistor, 20c per capacitor so 50c worth of parts! (and $10 for postage!)

Had you been local (UK based) I'd send you the stuff FOC.
LOL. Right- shipping is the most expensive item! Favor- can you search Amazon for those 2 parts and send a link? OR, I can email Mouser(?). Who is Mouser?
 

kellys_eye

Jun 25, 2010
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These are 'typical' parts although my UK site says 'unavailable' and these are all packs of 10 or 50(!) (you can't buy them singly from Amazon). You can use the descriptions to find them on eBay or at Mouser

https://www.mouser.co.uk/?_gl=1*kxb...QT4T*dW5kZWZpbmVk*_ga_1KQLCYKRX3*dW5kZWZpbmVk

or RS Components or Farnell or Rapid etc etc. Just Google 'electronic components' for the most popular supplier in your country to flag up as first result.

Note - I've over-spec'd the capacitors (630V+ devices) but anything over 100V will do. Not a lot of difference in price however.
 

danadak

Feb 19, 2021
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Just checked for ohms and the meter shows no reading, meaning no resistance. I also clicked the meter at the ring/buzzer tone mode and got no tone. So now, I think we know it must be a bad filter, right? Options to make? What parts? Can I buy from Amazon?
Thanks, people.
When you have no reading, was that 0 ohms or infinity ohms ? Post a pic pic your
meter....


Regards, Dana.
 

noquacks

Jun 26, 2013
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When you have no reading, was that 0 ohms or infinity ohms ? Post a pic pic your
meter....


Regards, Dana.
I should have clarified- it did not read 0, but it stayed at 1 (infinity??). In other words, the 1 showed on the screen before I touched the 2 terminals and it stayed at the same #1 when touching. Same as if terminals were in the air. Then, I switched it to ring upon touching resistance, and got no ring at all. Doesnt this mean no resistivity with no ring?
 

danadak

Feb 19, 2021
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It means cap still has its dielectric intact, at the LV that the meter uses.

Generally says cap may be OK,unless its actual capacitance has changed and circuit
no longer can function. Can your meter measure capacitance ?

Generally the scale with buzzer is a continuity indicator, low resistance, consult manual
for what low R that means.

You might consult youtube for a video on using a basic DVM, to give yourself some
additional knowledge.

Regards, Dana.
 

kellys_eye

Jun 25, 2010
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Could be a case of the connecting wires (to the filter) being broken - usually at the point of entry/exit. Use a 'pin' to penetrate the insulation at either end of the filter and test across the pins. If there is a measurable resistance (as stated in #2 above) then you might have some success in cutting and remaking the wires right at the entry/exit points.

The resistance values are 'high' (in the scheme of things) and the capacitors are not the type that usually suffer random failure - the components are not NORMALLY prone to failing so I'd be suspect of the flexible wires breaking - a very common issue - than the parts inside the filter actually being dud.

Another thing to check is the physical connection of the metalwork of the filter as this is the 'ground' connection to the components. Are the mounting surfaces clean enough to make a good connection? Is the actual mounting point physically and electrically ground (use your meter for testing ground continuity).
 
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noquacks

Jun 26, 2013
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Could be a case of the connecting wires (to the filter) being broken - usually at the point of entry/exit. Use a 'pin' to penetrate the insulation at either end of the filter and test across the pins. If there is a measurable resistance (as stated in #2 above) then you might have some success in cutting and remaking the wires right at the entry/exit points.

The resistance values are 'high' (in the scheme of things) and the capacitors are not the type that usually suffer random failure - the components are not NORMALLY prone to failing so I'd be suspect of the flexible wires breaking - a very common issue - than the parts inside the filter actually being dud.

Another thing to check is the physical connection of the metalwork of the filter as this is the 'ground' connection to the components. Are the mounting surfaces clean enough to make a good connection? Is the actual mounting point physically and electrically ground (use your meter for testing ground continuity).
Thats something to follow up on, Kelly. Who Knows- maybe bad wires on a still good filter. Will try this tomorrow.
 
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