tach problem
Thread Starter
Racer
Joined: Aug 2005
Posts: 315
Likes: 0
tach problem
ok My tach isn't working,it stays around 2000rpm.when I start the car it will move a bit ,meaning maybe it's the printed circuit board behind the tach.But then again I ain't sure,it could also be the tach filter.
I checked the filter with a ohm meter and it reads,but I don't know what it 's supposed to read.Does anyone know what the resistance should be?or should I just replace the circuit board since I get a reading from my meter on the filter.
I just don't want to replace something that is still good
thanks
I checked the filter with a ohm meter and it reads,but I don't know what it 's supposed to read.Does anyone know what the resistance should be?or should I just replace the circuit board since I get a reading from my meter on the filter.
I just don't want to replace something that is still good
thanks
Drifting
Joined: Oct 2003
Posts: 1,330
Likes: 1
From: Kerrville Texas
I'm pretty sure the Tach Filter is not your problem. The filter eliminates spiking? if the filter doesn't work you won't see any activity on the tach at all.
Somebody else correct me if I'm wrong.
Kona
Somebody else correct me if I'm wrong.
Kona
Pro
Joined: Dec 2004
Posts: 570
Likes: 0
From: glace bay nova scotia
In my 75 the circuit board in the tach fried a circuit and was doing exactly what you said.when i looked at mine i could see the track burned up across two points. I simply solderd a small wire from connection to connection where it was fried and away it went.
the big pain is to get the board out in your hand.it will save you 60 bucks if u don't need to buy one.
the big pain is to get the board out in your hand.it will save you 60 bucks if u don't need to buy one.
Thread Starter
Racer
Joined: Aug 2005
Posts: 315
Likes: 0
that's a good idea.I've checked the circuit board and there seemed to be a burnt spot on it where a resistor is not reading with my ohm meter.
But would it be dangerous to fry something else by jumping that resistor?
But would it be dangerous to fry something else by jumping that resistor?
Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
The burnt part sounds like a zener diode, not a resistor.
When they fail, they fail short, which then blows the 12V trace.
Remove the part.
Jumper the blown trace.
This happened to mine and a board I saw in this thread:
http://forums.corvetteforum.com/show...540&forum_id=3
Can you post pics of both sides of the PCB to confirm?
gvn
When they fail, they fail short, which then blows the 12V trace.
Remove the part.
Jumper the blown trace.
This happened to mine and a board I saw in this thread:
http://forums.corvetteforum.com/show...540&forum_id=3
Can you post pics of both sides of the PCB to confirm?
gvn
Thread Starter
Racer
Joined: Aug 2005
Posts: 315
Likes: 0
Originally Posted by Kilroy1024
The burnt part sounds like a zener diode, not a resistor.
When they fail, they fail short, which then blows the 12V trace.
Remove the part.
Jumper the blown trace.
This happened to mine and a board I saw in this thread:
http://forums.corvetteforum.com/show...540&forum_id=3
Can you post pics of both sides of the PCB to confirm?
gvn
When they fail, they fail short, which then blows the 12V trace.
Remove the part.
Jumper the blown trace.
This happened to mine and a board I saw in this thread:
http://forums.corvetteforum.com/show...540&forum_id=3
Can you post pics of both sides of the PCB to confirm?
gvn
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Thread Starter
Racer
Joined: Aug 2005
Posts: 315
Likes: 0
[IMG]
[/IMG]
Hope this works
Where I put arrows is where I don't get any reults with my ohm meter.But it's probably not the way to test 'em,I ain't sure.
I've checked the traces and all seem to be fine
[IMG]
[/IMG]
[/IMG] Hope this works
Where I put arrows is where I don't get any reults with my ohm meter.But it's probably not the way to test 'em,I ain't sure.
I've checked the traces and all seem to be fine
[IMG]
[/IMG]
Last edited by 80_vette; Aug 22, 2005 at 02:40 PM.
Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
Yeah, I'm here...
The circuit has changed quite a bit from the 76-77 version.
I think the part your pointing out is a .0047 uF capacitor.
It will read open with your meter.
Give me a few minutes to sort out this circuit.
I think the part your pointing out is a .0047 uF capacitor.
It will read open with your meter.
Give me a few minutes to sort out this circuit.
Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
Tach Info
Ive posted a couple of quick voltage checks on a website:
http://members.shaw.ca/gvn/index.html
See the 1980 page, I used your picture, I hope that's OK?
I will try and add a schematic later in the week.
Could you please tell what the rest of the numbers on D2 are?
It looks like a 1N52XX.
I'm expecting it to be something like a 1N5232, which should measure close to ~6V.
I can tell you what that voltage shoud be if I have the number.
gvn
http://members.shaw.ca/gvn/index.html
See the 1980 page, I used your picture, I hope that's OK?
I will try and add a schematic later in the week.
Could you please tell what the rest of the numbers on D2 are?
It looks like a 1N52XX.
I'm expecting it to be something like a 1N5232, which should measure close to ~6V.
I can tell you what that voltage shoud be if I have the number.
gvn
Thread Starter
Racer
Joined: Aug 2005
Posts: 315
Likes: 0
ok I need some ppl opinion.I am ready to buy new stuff,I either need a new circuit board or the tach filter.From some of you guys experience,which one is more likely to fail?some tell me the board and others say the filter............. 
anybody want to give me their opinion?
anybody want to give me their opinion?
Burning Brakes
Joined: Aug 2004
Posts: 856
Likes: 2
From: Tyler Texas
I had two tach filters go bad in a ten year period in my 1980 L-82. Never had a circuit board go bad--but some people have had that problem. Most people it seems find the problem is the filter. I would replace that first.
FYI: I have an "extra" complete 1980 L-82 tach unit (6,000 rpm redline; L-82 on the face) if you are interested and find it is not the tach filter.
FYI: I have an "extra" complete 1980 L-82 tach unit (6,000 rpm redline; L-82 on the face) if you are interested and find it is not the tach filter.
Racer
Joined: Sep 2004
Posts: 482
Likes: 1
From: Brandon Manitoba
I have gone through the total gamut trying to get my tach to work. I have replaced the printed circuit, tach board and the tach filter with no sucess.My last advise from the forum was that the tach board that I got was from Ecklers and they regularly sell brand new boards that do not work. I have signal from my distributor yet my tach never moves. My advise being if you need the tach board get it from Corvete Central. Brent