HOWTO: Tachometer Repair (WAS:Tach is all caddywhompus)
#31
#32
#33
LM1819 Air-Core Meter Driver
General Description Features
The LM1819 is a function generator driver for air-core
(moving-magnet) meter movements A Norton amplifier and
an NPN transistor are included on chip for signal condition-
ing as required Driver outputs are self-centering and devel-
op g 4 5V swing at 20 mA Better than 2% linearity is guar-
anteed over a full 305-degree operating range
Self-centering 20 mA outputs
12V operation
Norton amplifier
Function generator
Applications
Air-core meter driver
Tachometers
Ruggedized instruments
#34
Yeppers. I solved Gary Lewis' tach reading too high in just a couple minutes time. His was a DS3 - DS2 conversion.
Near the DS2 box is a connector with 2 wires, 1 green, 1 black. The green wire goes to the coil, and the black wire goes to ground, but ONLY on a V8 truck. A factory 6 cyl truck will not have the black wire on the engine side of that plug.
As for the crud inside the tach causing erratic behaviour, these trucks are not the only ones that suffer from the issue. I need to disassemble the tach in my RX7 and clean it up. It works fine, till the temp drops to under 40F. I rarely remember about, since I rarely drive the car in temps cool enough to cause the tach to "wig out".......
Near the DS2 box is a connector with 2 wires, 1 green, 1 black. The green wire goes to the coil, and the black wire goes to ground, but ONLY on a V8 truck. A factory 6 cyl truck will not have the black wire on the engine side of that plug.
As for the crud inside the tach causing erratic behaviour, these trucks are not the only ones that suffer from the issue. I need to disassemble the tach in my RX7 and clean it up. It works fine, till the temp drops to under 40F. I rarely remember about, since I rarely drive the car in temps cool enough to cause the tach to "wig out".......
Thanks
#35
This wire is also the sole point of ground for the entire in IGN system. So if the engine runs ... the ground wire is good.
Not really sure if this answers your question or not.
Jim
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#38
Instrument panel
Hey fellas,
I have an Australian 1983 f100xlt 351c. I will be taking the in instrument panel/gauges out again as my Tacho is not working,and will post a picture of the rear circuitry . Ive read that the 1980 models in the US have a green circuit on the back and from 1981 on it changed to red. Well maybe we just got old stock over here. They tell me that the ones over here were a Canadian build etc . So I will send yall a pic
Cheers
I have an Australian 1983 f100xlt 351c. I will be taking the in instrument panel/gauges out again as my Tacho is not working,and will post a picture of the rear circuitry . Ive read that the 1980 models in the US have a green circuit on the back and from 1981 on it changed to red. Well maybe we just got old stock over here. They tell me that the ones over here were a Canadian build etc . So I will send yall a pic
Cheers
#39
I just wanted to revive this thread to assure members that this thread is worth its weight in gold. This past weekend, while at the 2016 OK-GTG, the tachometer in my 1986 F150 was taken out and cleaned as detailed on page #2 of this thread and it worked as described! Thanks to Gary Lewis for his "hands on" assistance!
The inside of mine was no where near as "bad" as the one shown in this thread, but the tachometer still was not performing properly and after the cleaning, it reads correctly, again.
The symptoms of my truck's tachometer was this: it read 50+% high. It was as though both the 6 cyl. and 8 cyl. circuits were both being activated? Anyway, after cleaning, the tachometer is working beautifully.
The inside of mine was no where near as "bad" as the one shown in this thread, but the tachometer still was not performing properly and after the cleaning, it reads correctly, again.
The symptoms of my truck's tachometer was this: it read 50+% high. It was as though both the 6 cyl. and 8 cyl. circuits were both being activated? Anyway, after cleaning, the tachometer is working beautifully.
#40
#41
Hi, old thread, I know but...
if you are going to do this be careful when doing the top of pcb (where all the components are). There is a rheostat (adjustable resistor) on the bottom left (on mine anyway) that you don't want to turn. I Believe it may be used for calibration of the tachometer, don't know for sure but try not to let it turn anyway. Better safe than sorry.
Sully
if you are going to do this be careful when doing the top of pcb (where all the components are). There is a rheostat (adjustable resistor) on the bottom left (on mine anyway) that you don't want to turn. I Believe it may be used for calibration of the tachometer, don't know for sure but try not to let it turn anyway. Better safe than sorry.
Sully
#42
Necro post I know, but wanted to add to this discussion. My Tach on my '81 150 4.9 4speed (Srod), had a tach that would only work on really cold mornings until there was some heat in the cab. Then go dead. I checked the wiring from the ds2 to the tach, green with some color trace, ohmed out to tach. With truck running had 12v to tach, good ground and a fluctuating voltage on other pin. Don't remember the label.
I took the instrument cluster out and found tach had cover, 2 Phillips head screws and four brass nuts with washers holding it together. disassembled, and found the ground contact pin loose when tach tightened. There is a post that the underneath of the circuit board touches to provide ground to coils for the tach. added solder to raise the height of the post, and reassembled, tach now works fine.
I am located in E. TN. and it was in the upper 40's today. Sorry I didn't take any pictures otherwise I would have been more specific as to details.
LNK
I took the instrument cluster out and found tach had cover, 2 Phillips head screws and four brass nuts with washers holding it together. disassembled, and found the ground contact pin loose when tach tightened. There is a post that the underneath of the circuit board touches to provide ground to coils for the tach. added solder to raise the height of the post, and reassembled, tach now works fine.
I am located in E. TN. and it was in the upper 40's today. Sorry I didn't take any pictures otherwise I would have been more specific as to details.
LNK
Last edited by Lnk; 12-22-2018 at 06:29 PM. Reason: punctuation and spelling
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