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Discussion Starter · #1 ·
Does anyone know if you can bench test a constant voltage regulator (instrument voltage regulator) to figure out what is going on?
Water temp and fuel guages aren't working. I've traced wires from the grounds through the sensors to the guage cluster connector, all are good. 11.89 volts at the onnector with the engine off, all traces on the guage cluster show continuity, guages show around 10 ohm resistance. The guages, however, don't work. I replaced the old CVR with a new one (Sixty five bucks?) but the guages still don't work. Its possible I now own two bad CVR's, but I'm wondering if I can bench test this?

Carl
 

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Connect input side to battery, output side to battery negative. Use DVM to measure output: it should be a variable reading on DC volts, and non-zero on a AC volt setting. The CVR changes state from 12V to 0 V about once a second, which is too fast for some DVM's and too slow for others.

I'll bet your ground path from the CVR to chassis ground is bad.
 

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Carl,

You should be ab;e to test it without removing from the dash. 12V on the input, 4-6 volt (very variable as Midlife stated) on the output. Is there more than one CVR on your cluster? If not and if you have oil pressure gauge its not the CVR.

You had your gauges at Hatboro didn't you. At least the water temp? We were all talking about how hot we were running!

I'll also second Mid's ground statement. If your cluster isn't properly grounded, you's CVR won't work properly in place.

Good luck.

Frank
 

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Discussion Starter · #4 ·
I have 0 volts at the senders, ac or dc, using two dvm's and one analog vm. I disconnected the signal lead from the senders, and measured there. My ground reads 0.3 ohms resistance at the connector for the cvr (from chassis). The ground between the connecter and the housing of the cvr reads 0.2 ohms. Each sensor lead between the connector, through the senders, to ground, read about 220-230 ohms. Unfortunately, I can't get at the points on the plastic circuit to measure once the two are connected, but I cleaned the contacts, re-sprung the contacts on the connector, and have tested each lead through the printed circuit.
The original cvr reads 62 ohms between power and ground, 0.1 ohms between power and the instrument leads (if it was bad, wouldn't this lead to pegged guages?) The new cvr reads 60 ohms between power and ground, open between power and the instrument leads.
I guess I'll go buy a little 12v battery to try and set up a powered test, because this is driving me crazy.
As for Hatboro, I didn't have the in-dash fuel or temp guages (everything else works), just the autometer set under the passenger cowl for temperature, oil pressure, and volts. Since the car is a tach car, there is no in-dash oil pressure guage, just an idiot light (which is presently awol).

HELP!!!

Carl
 

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Your resistances you measured seem normal. Remember, there's two states for a CVR: open and closed. Depending upon what state it was left, it could be seen as having little resistance from power to output or very high resistance from power to output.

You can use the car battery itself, or a nearly dead one if you have that handy. A bunch of C or D cells can also work for testing the CVR.
 

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The CVR is just a bi-metal switch that opens and closes. The duty cycle ( On time ) was around 60-70% if I recall. It turns on and off ( one cycle ) about once per second. As a recall, my fuel, temp, and oil pressure guages were about 12.5 ohms. These three are the same guage with just a different face. If you connect a 1.5 volt A, C, or D cell to the input lead of any of these 3 guages, you'll get about 1/4 to 1/3 deflection. If no movement, then the guage is bad. All of this info is applicable to a 65-66 GT guage cluster.
 
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