TESTING THE HEATER CIRCUITS OF A
TRIAC/OPTOCOUPLER SYSTEM
ELECTRICAL PATH FOR EACH CIRCUIT
When the temperature controller sense (by way of
the thermocouple) a cooling of the heating
element, it sends low voltage DC current to the
optocoupler. The optocoupler act as a normally
open switching device which closes when it
receives a signal. This allows a flow of electricity
through the optocoupler and triggers the triac. The
triac is another normally open switching device that
is capable of carrying up to 40 amps current.
When the triac closes, the current is able to pass
through the heating element. The other side of the
element is connected to the power block, This
action causes the panel to heat. When the
controller senses the elements are at operating
temperature, it shuts off the current to the
optocoupler which causes the flow of electricity to
the panel to cease. This is when the system
begins “cycling”. The heater indicator lamps blink
on and off. With every cycle, the triac and
optocoupler switches on and off.
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TOOLS NEEDED:
Volt/Ohm Meter
In this instruction sheet, terminal strip refers to the white connecting strip inside the control
box. Power block refers to the block where the incoming power lines connect.
To check the Triacs:
The triacs are located inside the control box on the aluminum heat sink in the upper left corner.
There will be one triac for each heating element.
Disconnect the power to the unit at the main breaker/fuse box so that you can make a
visual inspection of the heater circuit wired and connections. You will need to
reconnect the power later to make voltage checks.
1. Open the cover to the control box.
2. Visually and physically check the wires and connections at the terminal strip and at
each triac. Replace any worn wire(s) with wire of the same type and rating.
3. With the power still disconnected, perform an ohms test on each circuit. Locate the
two wires coming from the individual heaters. The wires connect into the strip starting
at the right end. In a single phase unit, they will be labeled 1-1-, 2-2, 3-3, etc. In a
three phase unit they will be labeled A-1 B-1, B-2 C-2, C-3 A-3, A-4 B-4, B-5 C-5, etc.
Remove the two heater wires for each panel from the terminal strip. Place one lead
from the ohmmeter to each of the incoming heater wires. (check only one set at a time
and then reconnect to avoid mixing the wires with each other panels). There should be
continuity at each panel. If a panel does not have continuity, then check the individual
heater panels and/or crimps inside the heat chamber.
4. Reconnect the power at the breaker box. Be careful from this point on as the power
will be live to the components you are checking.
5. Again, locate where the heater wires connect into the terminal strip.
6. Set the voltmeter to the 250 (or greater) AC volts range.
7. First check the voltages with the HEAT switch off. There should be NO voltage
readings at this point. If there is voltage across a heater, then the triac for that heater
circuit is stuck in the closed position and it should be replaced.
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8. Turn the HEAT switch on and increase the temperature setting approximately 100
degrees above the normal setting. Again check the voltages, this time while the dryer is
constantly heating. There should be a constant 208-240 volts (depending on the
incoming voltages). If there is no voltage on any circuit, then that triac is stuck in the
open position, or the optocoupler board is not sending the signal to the triac for it to
close (see “Testing the Optocoupler Board” section).
9. Lower the temperature back to the normal operating temperature. Let the dryer heat up
to operating temperature and the controller cycles. Check the voltages again. The
readings should fluctuate between 0 volts and the incoming line voltage.
10. If the voltages are correct to all heater panels, then the problem is not in the electrical
circuits controlling the heater(s).
If there is a problem with the heater circuit, then you should check the optocoupler to make
sure it is functioning properly. Each triac has an optocoupler than controls the switching
action. IMPORTANT: Before making any electrical checks, visually inspects the optocoupler
to make sure it is not cracked or damaged. The “dimple” must be in the lower left corner.
Also, visually inspect each of the small resistors on the board.
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Testing the Optocoupler Board:
To check the input side of the optocoupler:
1. Set the voltmeter to DC volts (50 volts or less range).
2. Place the BLACK lead of the voltmeter to the negative (-) terminal on the terminal strip.
3. Place the RED lead of the voltmeter to pin #1 of the left most optocoupler. There
should be approximately 7.5 volts DC at this position for a 5 heaters system; 6 volts for
4 heaters; 4.5 volts for 3 heaters; 3 volts for 2 heaters.
4. Move the red lead to pin #2 of the same optocoupler. There should be a 1-1/2 volt drop
from the previous reading.
5. Move the red lead to pin #1 of the next optocoupler. The reading should be the same
as pin #2 of the previous optocoupler. Check the voltage again at pin #2. There should
again be a drop of 1-1/2 volts.
6. Check all optocouplers in this manner. The voltage at the #2 position of the last
optocoupler should be 0.
7. if any optocoupler has a voltage reading at pin #1 but not at pin #2, then the optocoupler
should be replaced.
8. if any optocoupler had no reading at pin #1 but the previous optocoupler had a reading
at pin #2, then the whole board should be replaced.
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To check the output side of the optocoupler:
1. Set the voltmeter to the 250 volts AC range.
2. Turn on the heat switch to the dryer. Make sure the temperature controller is calling for
heat (the L1 light on the controller should be on).
2A. Single Phase Units: Place one lead of the voltmeter to pin #6, (see accompanying
electrical drawings) place the other lead to T-3. There should be approximately 220
volts at this point. Move the lead from pin #6 to pin #4 and check. The voltage should
be the same at this connection as it was at pin #6.
Check all optocouplers using this procedure. If any optocoupler has a reading at pin #6
but no reading at pin #4, AND the controller is calling for heat, then the optocoupler
should be replaced.
If any optocoupler has no reading at pin #6, then the optocoupler board should be
replaced.
2B. Three Phase Units: Place one lead to pin #6 (see accompanying electrical drawings)
and the other lead to an opposing leg of the system; (check optocoupler #5 to C; #4 to
B; #3 to A; #2 to C; and #1 to B). There should be 220 volts (or live voltage). Move the
lead to pin #4 and check in the same manner. The voltage should be the same as at
pin #6. Follow this procedures to check all optocouplers. If any optocoupler has a
reading at pin #4 but not pin #6 AND the controller is calling for heat, then the
optocoupler should be replaced.
If there is no voltage at pin #6, then the board should be replaced.
3. If the voltage readings are correct at all optocouplers, leave the one lead on the
opposing leg (see 2A and 2B for correct locations). Move the other lead to the 6 o’clock
position of the triac to check the voltage at the triac. If there is no voltage, then check
the wires and connections. If the connections are ok, then the board should be
replaced.
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