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Old 07-31-2020, 07:13 AM   #1
volvowagoon
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Default Botched Small Tach Installation or Bad Gauge?

I just got around to installing a very nice looking small tach which I bought here on the board. Sadly, it doesn't work all the time. Sometimes it works just fine and then it drops in and out randomly. During my commute this morning, it came to life for about 5 seconds before dropping out again.

After pulling the cluster out to try diagnosis, I had been unable to find anything wrong. The light and tach have a common ground and the light works flawlessly. I sourced gauge power directly from fuse 13. When I check for power and ground with the car running I have a steady drop of 12V at the gauge terminals.

The only thing worth looking at now is my tach signal. Is it bad that I have the signal split to two devices? This car came with a remote start system, so I'm using the same white/red wire for that as well. Maybe my signal is getting pulled into that? When I get a chance I'll try to run a separate wire from the coil.
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Old 07-31-2020, 07:31 AM   #2
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Originally Posted by volvowagoon View Post
The only thing worth looking at now is my tach signal. Is it bad that I have the signal split to two devices? This car came with a remote start system, so I'm using the same white/red wire for that as well. Maybe my signal is getting pulled into that? When I get a chance I'll try to run a separate wire from the coil.
Yes, that is worth looking into. Instead of running a separate wire, which would do nothing to reduce a load presented by the remote starter, why not just disconnect the remote starter from the tach signal to prove whether it is the culprit. If it is, I'd think your ignition itself (waveform) would also be compromised even though you don't notice the change.
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Old 07-31-2020, 10:23 AM   #3
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Yes, that is worth looking into. Instead of running a separate wire, which would do nothing to reduce a load presented by the remote starter, why not just disconnect the remote starter from the tach signal to prove whether it is the culprit. If it is, I'd think your ignition itself (waveform) would also be compromised even though you don't notice the change.
Good idea. Thanks, Art. We don't really use the remote starter unless we're trying show off anyway. I should really just remove it. It's become a rat's nest.
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Old 07-31-2020, 02:28 PM   #4
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I disconnected the remote start and ran the original tach signal directly to the gauge. No dice. I got rid of the wire completely and ran a long alligator from the negative side of the coil to the gauge terminal. Still nothing. Now I'm out of ideas.
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Old 07-31-2020, 02:58 PM   #5
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I think those VDO tachs have a similar issue as the clocks. There are some electrolytic caps inside them that dry out and cause the device to no longer function.
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Old 07-31-2020, 03:01 PM   #6
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Same issue with my big tach, comes and goes completely, accuracy is sometimes questionable also.
I think the caps idea is a good one, haven't seen fit to dig in to it just yet.
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Old 07-31-2020, 03:04 PM   #7
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I think those VDO tachs have a similar issue as the clocks. There are some electrolytic caps inside them that dry out and cause the device to no longer function.
Hmmm it kinda seems to operate that way too. Once it feels like working for more than about 5 seconds, it seems to work for the rest of the trip. Once you cut power, all bets are off.

Is anybody repairing these by chance? I'd sure hate to see it get scrapped because it's in such aesthetically nice shape. This is also the only one I've ever seen in person.
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Old 07-31-2020, 03:13 PM   #8
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Hmmm it kinda seems to operate that way too. Once it feels like working for more than about 5 seconds, it seems to work for the rest of the trip. Once you cut power, all bets are off.

Is anybody repairing these by chance? I'd sure hate to see it get scrapped because it's in such aesthetically nice shape. This is also the only one I've ever seen in person.
You might ask RP80242GT+T

He fixed a couple of 52mm clocks for me a while ago.
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Old 07-31-2020, 03:15 PM   #9
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See this thread also:
http://turbobricks.com/forums/showthread.php?t=281924
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Old 07-31-2020, 03:26 PM   #10
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Paging Philski, I’m pretty sure he’s recapped a few of the VDO clocks and may have some information on that.
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Old 07-31-2020, 03:34 PM   #11
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Quote:
Originally Posted by DD Ranch View Post
You might ask RP80242GT+T

He fixed a couple of 52mm clocks for me a while ago.
Will do. Thanks for the lead.

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Interesting. Yeah, mine bounces a little when it's actually working. I just kinda chalked it up to being an old tach although I knew it wasn't necessarily "normal". I've certainly seen far worse though! I wonder if a VDO/Volvo gauge specialist could fix it. I also wonder what that bill would be like.

I'll do some more digging after my vacation. I don't want to go in there, but I'm actually an instrumentation tech. It would be a bit embarrassing to send this out before at least giving it the old college try. Lol
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Old 07-31-2020, 04:08 PM   #12
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I forgot to mention cold solder joints. That happens on these being so old now. A cold solder joint where the spade connector is soldered can cause intermittent function.

To open those up is pretty easy. You gently pry the bezel off. I use a couple of small screwdrivers to get under the edge. Pry out the edge working your way around till it comes off. The bezel holds on the clear plastic to the gauge body so be careful. Once the bezel and glass are off you should be able to remove the circuit board. Been awhile so there may be a screw on the back to hold the board into the gauge.

Last edited by dl242gt; 07-31-2020 at 04:09 PM.. Reason: add comment
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