User guide

P/N: 021-00154, Rev. A.6 - updated for V4.7 Tools Page | 151
Flashing LEDs on HCT’s products usually indicate that a problem. How to isolate the cause of the problem is
what we will cover next.
HCT products typically have a power LED to indicate that there is enough voltage to run the specific
module/product. The power LED should be steady on! Off or flashing indicates a power problem and you must
find it and fix it before worrying about any other symptoms. Note that on our products that power LED will flash
steadily to indicate that the power supply voltage is higher than the maximum specified. When the power supply
is too high the units will shut down, which also turns off the power LED or makes it flash erratically. Check the
power and ground wires, switches, connectors and fuses to verify they are installed properly. If no obvious fault
is found, use the voltmeter to measure the voltage between power and ground with the unit plugged in and
drawing power if possible. Verify the reading against the unit’s power specification. All of our product
datasheets are available from our web site. Start at the unit and work your way back toward the power supply
till the problem is found. If you do not have a voltmeter, jump the product's power input to the battery to verify
that the power LED comes on. Now that you can trust the unit, move the jumper wires further down stream, past
switches, wires and connectors till the light goes out.
Our DVC10 and DVC50 products have variable current outputs for controlling proportional valves. Each such
PWM output has a red/green LED that gives a relative indication of the current output. If the PWM % LED is fully
red, the unit is not trying to drive much current or there is a short circuit. Disconnect the coil at the valve
housing and measure its resistance and compare it to the specifications. If the PWM % LED is fully green, the
unit can not drive as much current as it wants to, probably due to an open circuit or insufficient voltage for the
resistance to be driven. This can also be caused by adjusting the DVC unit to drive more current than is actually
required to do the job. In this case readjust the card if the system if functioning correctly but the PWM % LED is
fully green. If the system is not operating at the desired speed, disconnect the coil at the card and measure its
resistance and compare it to the specifications. If the coil is OK, measure the power supply voltage at the card's
power input and coil output while the card is driving the coil. If the coil voltage is within a volt of the power supply
(typical, see card's specifications), the card is functioning correctly. You may reduce the voltage drop from the
power supply to the card by shortening the wiring, using bigger wires or fewer switches and connectors.
Choosing a coil rated for less voltage can also solve this problem. If the PWM % LED is off, the unit is not trying
to drive that output, troubleshoot the inputs. Our DVC products flash the PWM % LED to indicate a short
(flashing red/off) or and open (flashing green/off).
Most of our products have single color LEDs to indicate the state of simple on/off outputs and some times the
state of inputs. Shorted on / off outputs are indicated by rapid flashing and open outputs by slow flashing. Error
LEDs come on or flash to indicate a wide variety of problems, see the unit specifications.
A good quality meter that can read DC voltage up to 50 volts, current up to 10 amps and resistance down to 1
ohm should be part of your tool kit. An extra battery is also a good idea. We recommend you buy a digital meter
to avoid having to figure out which analog scale you need to look at while the system is causing major noise and
confusion. There are many quality meters available, but Radio Shack is often the easiest place to find and has a
nice selection to choose from. Very important safety tip: The current range of the meter will measure the
maximum current the power supply can put out if you accidentally hook it across the power source! You must
also avoid hooking up the current meter correctly, but selecting a range that is too low. These actions typically
blow the fuse in the meter and usually a new fuse cannot be found easily. Make current measurements by
inserting a meter in series in the circuit. Make voltage measurements by connecting a meter across the circuit.
Make resistance measurements with the circuit turned off and disconnected from the rest of the machine by
connecting across the circuit. If blown current fuses prove to be a problem, HCT recommends that a 1 ohm, 10
watt resistor (Radio Shack or etc.) be temporarily spliced in series with the circuit and the voltage across the
resistor will reflect the current to be measured. A voltmeter hooked across the resistor will read the voltage drop
due to the current. The current is equal to the voltage for the case of a one-ohm resistor. Note that these
resistors are typically 5%, so the accuracy will be less than that of a current meter. Use a 0.1ohm resistor
(typically a special order) if the 1ohm resistor causes too much resistance in the circuit. Remember to multiply
the answer by 10 to get the current value. This resistor i
s also the easiest way to measure dither amplitude and
frequency with an oscilloscope, but be sure that the scope is floating with respect to ground (battery power or
use two wire AC cord adapter).