Augh... I've been out bidded... Gees you can buy it from year one for what 120 bucks? I want one to keep on hand since mine died but I also want to copy the layout and schematics to build a better one...
While fixing my original tach, at one time I copied down the schematic, really pretty simple. Don't know if the original GM schematic would help you though.
Scott, The only value I need is of the big coil on the original GM tach. I have all the other values its just the coil I need.
So... I wonder if this supplier made the tachs for everyone else as well. If that is true, that means there will be no more factory looking tachs... I guess I better get back into this auction...
John, I coil is actually a choke and it's resistance is around 200 ohms. I prevents the high current from reaching the tach circuitry. It's unusal for these to go bad. Brian
Thanks for the reply Brian. So its 200 ohms, 12 volts? I am going to get the parts this week to fix mine and I'm keeping my fingers crossed...
I'm really glad this supplier went out of business. That tach was absolutely useless (referring to the sticking issue), other than looking nice in the dash! This whole situation has really turned me away from Year-One as well. They knew this was a problem part but continued supplying them and not accepting returns because it is electrical and they were aware of the problem. I wonder why they didn't mention that when I ordered it?!?!!!!! What a CROCK!!!! :af: Yes, it was my tach on E-bay. I considered "Paying it Forward", but as much as that thing cost, I wanted to at least replace it with a good tach. I never thought it would go for that kind on money. WOW! I am super satisfied with the replacement, works correctly and looks really clean in the dash!!! Plus it was a TON cheaper! If anyone is wondering what I used, it was an Auto-Meter tach from Summit, Part no. ATM-2499. The price was $85.95. If your not looking for originality but quality that looks good, You will be happy with this.
If it is a choke you will also need to find the inductance (in mH) in addition to the dc resistance that you have. I don't have that value but it can be found by experimentation. It can be done with a known resistor, a voltage source and an oscilloscope - you want to find response time to a step voltage input. Or you can find it with a frequency generator, known resistance and an rms measuring voltmeter (or o-scope) - you measure frequency response. Oops, just realized, if yours is bad, you won't be able to measure it. ou:
I have something to add about the year one tach, I bought mine about a year or so ago, it works fine, (although I don't know how accurate it is)....but the lens it came with is rather foggy, compared to my clear originals, also, the backlighting is much brighter/it doesn't illuminate the same way as the the other gauges.
Scott, Good call on the choke. I have 3 dash tachs and 2 hood tachs so I can connect them to a scope and let you know the results. I can't do it for about a week since I am currently out of town. Brian
Brian, Just talked to a buddy of mine who works in a calibration lab, he says it would be easiest to just hook it up to an LCR (inductance-capacitance-resistance) meter. It will measure it directly. He has one. So if you want to remove the component and mail it to me, I can have him check it out.
Scott, After I get back next week I will mail it to you. Do you want the circuit board or only the choke? Brian