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Broken tach.. 67S
As soon as the ignition is switched on the tach needle just pegs on the other side. Any thoughts on what to check? Thanks, Bill
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Current: 1975 911S --Chocolate brown Past: 1967 911S --Bahama Yellow 1990 C2 Targa --Silver 1973 914 2.0 --Delphi Green |
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04-20-2004, 01:22 PM
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How about a bump after 3 months...
Any ideas??
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Current: 1975 911S --Chocolate brown Past: 1967 911S --Bahama Yellow 1990 C2 Targa --Silver 1973 914 2.0 --Delphi Green |
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07-30-2004, 07:35 AM
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The problem is inside the tach circuitry ... most likely a shorted transistor!
Analog tachs use a calibrated one-shot multivibrator to drive the meter, discrete circuitry back in '67 ... and about the only thing that could make the needle peg when power is applied ... is a short accross the output of that monostable, most likely the 2nd transistor itself.
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Warren Hall, Jr. 1973 911S Targa ... 'Annie' 1968 340S Barracuda ... 'Rolling Thunder' |
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07-30-2004, 08:19 AM
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If you took it apart and reverse engineered a schematic I'm sure all the EEs on the list would stumble over each other giving you trouble shooting steps.
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07-30-2004, 10:22 AM
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Thanks Warren, that gives me a place to start. I'll post more if/when I get it apart. Bill
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07-30-2004, 01:09 PM
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I've got a good one if yours is unfixable.
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07-30-2004, 02:28 PM
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Well, here's the inside of it. Doesn't do me much good though..
The connections left>right say 12V, 1, and -. Guessing the '1' is a lead from the ignition?? Anyway, I've got a volt meter and could hook this thing up to juice, but there's so many little diaode's and the like I'm not real sure if this is doable. Shaun, is your tach a S tach with the 7200 redline, if so how PM me what you'd like for it. Bill
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07-30-2004, 02:46 PM
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Oops, here's the pic.
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07-30-2004, 03:59 PM
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That pic won't help any! The carb. is in focus, but not the tach!
To be useful, the camera needs macro-focusing capability. Both sides of the printed circuit board are needed, in precise focus, and closely cropped, i.e., nothing else but the board! The numbers on top of the transistors should be in good, even light, and in focus.
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Warren Hall, Jr. 1973 911S Targa ... 'Annie' 1968 340S Barracuda ... 'Rolling Thunder' Last edited by Early_S_Man; 07-31-2004 at 07:12 PM.. |
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07-31-2004, 07:59 AM
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Yea, I guessed that pic wouldn't do much good. I'll play around with the camera (Canon a40) some more and see what I can do, not sure if it has macro mode or is just a limitation of the lens.
As another fix, Shaun has given me a fair price on his, but it's a 7000RMP. Are the internals the same, and could I mount my 7200 face on it?
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07-31-2004, 08:29 AM
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Warren, Here's some better pics. Let me know what else might be helpful. Thanks, Bill
    
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08-01-2004, 12:50 PM
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Bill,
Those are much better! I haven't seen such ancient transistor cases like that in use commercially since about 1965! Looks like three Valvo transistors ... 2 ea BC710, and an AC128. Actually, if you get the other tach ... I would recommend just swapping the board, and don't mess with your meter face or pointer. The 'guts' should be interchangeable!
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Warren Hall, Jr. 1973 911S Targa ... 'Annie' 1968 340S Barracuda ... 'Rolling Thunder' |
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08-01-2004, 04:06 PM
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Yeah, I was wondering that if I did somehow find which one was bad, how I'd find a replacement. I think I'll do just that and swap boards with a good one.
Oh well, at least I figured out how to use macro mode on my camera.
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Current: 1975 911S --Chocolate brown Past: 1967 911S --Bahama Yellow 1990 C2 Targa --Silver 1973 914 2.0 --Delphi Green |
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08-01-2004, 06:36 PM
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