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Both meters
were stuck up scale and totally useless. This is how I fixed the problem.
This isn't a construction article. If you decide to modify your supply
you may have to do things differently or use different parts. The
meters I used came from Marlin
P. Jones (http://www.mpja.com/) and were part number 12306 ME. |
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I completely
remove the panel and then measured, marked and enlarged the holes. |
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This is the
meter power board mounted in using existing holes in the bottom of
the supply. |
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The meter
power board. It has a 7805 regulator to provide +5 volts for the voltmeter
and an NE555 oscillator inverter to provide an isolated +5 volts for
the ammeter. This is built on a piece of prototype board and the schematic
is at the bottom of this page. |
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Back view
of the voltmeter. |
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Back view
of the ammeter showing the connection to the emitter resistor and
the 5k (measured 4.8k) potentiometer which parallels the 0.05 ohm
emitter resistor. The CCW lead connects to Ground on the meter and
to the output voltage end of the emitter resistor. The Arm connects
to Vin and the CW lead connects to the end of the 0.05 ohm emitter
resistor nearest the emitter connection. |
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Close-up of
the 5k pot used to adjust the voltage to the ammeter. The ammeter
is set up as a 200 mv meter and then calibrated using the 5k pot to
read properly. |
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Ammeter |
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Voltmeter |
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This is a
2.2k 1/2 watt resistor in series with an LED between the positive
and negative of the filter capacitors providing a low current bleeder
and indicator when there is voltage in the supply. Without a bleeder,
the capacitors will retain a charge for a very long time. After all,
there's 100,000 uf there! |
