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| Outta wack tach (Page 1/2) |
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PhatMax
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JUN 21, 05:05 PM
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Does anybody know if running a motor with the tach reading super high will affect the ignition system ?
A new Rodney tach filter was installed with the engine rebuild. The tach started out high but now it’s ridiculous….pegs out against the oil pressure gauge. I’ll be ordering the A new board from Red devil river eventually..
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olejoedad
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JUN 21, 07:37 PM
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Or send it to Forum member JGunsett......
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PhatMax
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JUN 21, 09:46 PM
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If I figure how to get it out….looks like you have to pull the whole pod out. If there is an easier way, I’m game
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Patrick
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JUN 21, 10:12 PM
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| quote | Originally posted by PhatMax:
...looks like you have to pull the whole pod out.
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...which is a lot easier than it might at first appear.
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theogre
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JUN 21, 11:41 PM
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The chip controlling the tach has 2 resistor/capacitor sets.
1 set total ark on the meter.
2 set total RPM in 1.
Cap's etc can go bad w/ little to no warning & will read way off.
Does nothing to the engine unless it or tach filter on HEI engines "shorts out" & keeps power flowing thru the coil killing that.------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave
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PhatMax
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JUN 22, 09:54 AM
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Thanks guys ! Does anybody know the values on the caps and resistors ? I have no problem soldering in new components . I have a Xytronic solder sucker and 2 Hakko 936 irons. I’d like to have the parts in hand before I tear it all apart so I can get it all done in a day.
Thanks again for the help.
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theogre
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JUN 22, 12:03 PM
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Cap values likely change for tach display & engine.
Main resistors do change for each tach because cap value tolerance can be ± 5% to 10% & "printed" on a "clip" that's laser/abrasive trimmed.
Old threads have you use 1 to 10 turn pot to fix but may not work if the cap(s) are bad.
The "chip" resistors can break anywhere on the ceramic then won't work. Is why adding a pot may work.
web search LM1819 driver chip for how it works
Likely No longer made but some places may still have data sheet.
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pmbrunelle
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JUN 22, 04:00 PM
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| quote | Originally posted by PhatMax:
Thanks guys ! Does anybody know the values on the caps and resistors ?
...
I’d like to have the parts in hand before I tear it all apart so I can get it all done in a day.
Thanks again for the help. |
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Considering that typical capacitor tolerances are on the order of +/- 10%, it's fairly impossible to choose both component values ahead of time and have the tachometer be accurate.
That's why the factory trimmed the resistor in the first place.
You should plan on some sort of calibration procedure and a trimpot. A reference RPM can be generated by cruising at a known speed, and calculating RPM via tire diameter, gear ratios, etc (auto trans must have its torque converter locked).
I have a thread about this topic, unfortunately I can no longer find the datasheet for the chip. Perhaps a copy can be found on the wayback machine.
https://www.fiero.nl/forum/Forum2/HTML/138637.html
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theogre
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JUN 22, 06:34 PM
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or just read https://www.fiero.nl/forum/.../HTML/138637.html#p5
ON Semi CS8190 have updated the chip that include Return to Zero feature but isn't pin compatible w/ LM1819 (& CS289 from Cherry) so haven't bother to read the sheet. I don't know if the meters in Fiero etc will work w/ the ON chip either as LM say 225Ω while ON say 200Ω & 25Ω dif may not matter or fries the ON chip.
E2A--> Ebay sellers of new tach boards all seem to use CS289 they get new from somewhere. Cherry is 1 of several brand bought up / spun off to ON semi that may have old stock some place but can't find Digikey etc selling them. Onsemi has CS289 PDF has Archive watermark https://www.onsemi.cn/downl...heet/pdf/cs289-d.pdf[This message has been edited by theogre (edited 06-22-2024).]
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J Gunsett
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JUN 23, 08:49 AM
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