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66' VDO tachometer Schematic
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Tonyspit
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PostPosted: Tue Jan 31, 2012 5:11 pm    Post subject: 66' VDO tachometer Schematic Reply with quote

Hi,

I have an old 66' VDO tachometer that I need to repare but I can't found the schematic... Sad

Does anybody here could have it to help me?

Thanks a lot,
Tony

here my tachometer:

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mrbigmax
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PostPosted: Wed Feb 01, 2012 11:31 am    Post subject: Reply with quote

The wiring is as follows:
+12 = +12 source the switches on when the ignition is switched on.
- = Chassis ground
1 = Connects to the "-" side of the ignition coil, the same side as the condenser.
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KTPhil Premium Member
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PostPosted: Wed Feb 01, 2012 11:47 am    Post subject: Reply with quote

I think he meant the internal schematic, not the external wiring.

Not much to it; if you can see the other side you could probably draw it up yourself. Not sure what good it would do... you can test for opens or shorts with a VOM, that's about all.


Last edited by KTPhil on Wed Feb 01, 2012 1:14 pm; edited 1 time in total
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Tonyspit
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PostPosted: Wed Feb 01, 2012 12:43 pm    Post subject: Reply with quote

You're right KTPhil, I'm looking for the internal schematic.

Yes, I could draw it myself by following the wire on the board... but it would be long and the risk of doing a mistake is big...
Moreover, I need the schematic to check the components values.
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KTPhil Premium Member
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PostPosted: Wed Feb 01, 2012 1:23 pm    Post subject: Reply with quote

Tonyspit wrote:
You're right KTPhil, I'm looking for the internal schematic.

Yes, I could draw it myself by following the wire on the board... but it would be long and the risk of doing a mistake is big...
Moreover, I need the schematic to check the components values.


What components are on the board? Diodes and resistors are often color-coded so you can read the values. Transistors are usually stamped with a P/N. Usually, circuit card failures are in cold solder joints, broken traces or wires, and open/shorted components, not value deviations.


Last edited by KTPhil on Wed Feb 01, 2012 11:59 pm; edited 1 time in total
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Tonyspit
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PostPosted: Wed Feb 01, 2012 4:03 pm    Post subject: Reply with quote

Basically, I need the schematic because the variable resistor is tuned on the max and the value indicate by the tachometer isn't good.
When the motor is at 2000rpm, the tachometer indicate 1600rpm.
I thought I could change the variable resistor of 500 ohms by an other of 1k ohm but I would be sure it won't affect the others components.
Moreover, I would check the thermistor value that colors aren't visible anymore.
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Tonyspit
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PostPosted: Fri Feb 03, 2012 2:59 am    Post subject: Reply with quote

So, nobody has this precious schematic? Sad
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KTPhil Premium Member
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PostPosted: Fri Feb 03, 2012 9:57 am    Post subject: Reply with quote

No, but since this was not a VW accessory that is not surprising. You might have better luck on a board focused on whatever vehicle that tach came from.
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Tonyspit
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PostPosted: Fri Feb 03, 2012 1:37 pm    Post subject: Reply with quote

But it was a VW accessory, rare but real.
It fitted the rare Beetle Mach 1.

Look at her:

Image may have been reduced in size. Click image to view fullscreen.


and inside, we can see the tacho:

Image may have been reduced in size. Click image to view fullscreen.


(Picture taken from the Flat4ever website).

It wasn't really a vw model so the tacho may fitted an other car but I don't know which car...
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PostPosted: Sat Feb 04, 2012 11:54 am    Post subject: Reply with quote

Yes, almost certainly for other cars, since in '66 the VW was 6V, and that unit is 6/12V compatible.

Have you tried googling the numbers on the case? You might find something that way.
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Tonyspit
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PostPosted: Sun Feb 05, 2012 5:27 am    Post subject: Reply with quote

Yes, I tried to search the serial number of the electronic circuit on google but I didn't find... Sad
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PostPosted: Sun Feb 05, 2012 10:39 am    Post subject: Reply with quote

Try contacting North Hollywood Speedometer. They do a lot of gauge repair and might either have the info or can fix it for you.

http://www.nhspeedometer.com/
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Tonyspit
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PostPosted: Sun Feb 05, 2012 11:08 am    Post subject: Reply with quote

Email sent!
Thank you KTPhil ! Smile
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Tonyspit
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PostPosted: Tue Feb 07, 2012 3:33 am    Post subject: Reply with quote

Answer received: they haven't any VDO schematic of circuit board... Sad
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bruce jones
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PostPosted: Tue Feb 07, 2012 5:03 am    Post subject: Reply with quote

I would suggest you contact H&H Auto Electrical, in Greer, South Carolina. They restored the tachometer in my 1965 Chevrolet, and I am very happy with their work.

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Image may have been reduced in size. Click image to view fullscreen.


The telephone number for H&H Auto Electric is (+1) 864 895 4404. I don't know if they have the schematic you seek, or if they will service a VDO instrument, but it may be worth a call.
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PostPosted: Tue Feb 07, 2012 8:25 pm    Post subject: Reply with quote

Bruce, thanks for the unintended info. The odometer on my '66 doesn't work, so I'm going to give them a call. As it happens, I live in Greenville, SC.

Tony, you may have already called them, but I'll ask in the morning while getting a quote on my VDO speedometer. I lived in Ireland for a while, so I know how much international rates are, even on Skype.
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Wayne S. Johnson
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PostPosted: Tue Feb 07, 2012 9:45 pm    Post subject: Reply with quote

R2 is the calibration resistor, replace it with a pot with twice the measured value. Adjust the pot for a reading of 1200 RPM @ 60 Hz input frequency. The lower left part of circuit doesn't look correct.

http://forums.pelicanparts.com/porsche-911-technical-forum/266707-early-vdo-tachometer-guts-2.html

http://forums.pelicanparts.com/porsche-911-technical-forum/159346-broken-tach-67s.html

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PostPosted: Tue Feb 07, 2012 10:34 pm    Post subject: Reply with quote

You could replace the old board with this LM555 circuit.
Remove IC1 for 6 Volt systems.

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PostPosted: Wed Feb 08, 2012 5:03 am    Post subject: Reply with quote

bruce jones : thanks but I'm afraid that they 'll say the same thing than North Hollywood Speedometer (no schematics but they could repair if I send my tacho).

Wayne S. Johnson : thanks for the 2 topics, even if they talk about a 911 tacho, it's a good beginning.


Otherwise, I changed the variable resistor of 500 ohms to a 1k ohms.
I realised that there were only 2 connectors used of the 3.
It's a good new because it's easier to understand.
Now, the tacho work (even if there is still a problem when the car stay some hours out in the cold) but I'm still interesting in the schematic.
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PostPosted: Wed Feb 08, 2012 5:52 am    Post subject: Reply with quote

From what I can see, on the connector is present the "+6V" pin, to use on 6V cars, but I can't see the hole below it.

The '12V' indication on the chassis seems to refer to an "only 12V" device.

Looking at the printed circuit board I notice some empty holes, probably they are for a full '6V/12V' unit.

If you find the real schematic for this device, I can try to suggest you missing electronic components to enable 6V working.
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