PWM3E/F Functional Information

J1 External PWM Master Disable, Short to Disable Onboard PWMs 1-3
J2 Single Supply Enable, Short to Tie MOSFET Gate Supply TB3 to +DC
J3 Common Ground Enable, Short to Tie MOSFET Source to -DC
J4 Auxillary TTL Inputs 1, 2, 3, & Gnd
SW1 1-3 = PWM Channel Disable 4 = PWM Master Disable
TB1 DC Power Input & MOSFET Source Ground
TB2 MOSFET Drain/PWM Outputs & MOSFET Gate Supply Input

Expanded Connection Information

J1 is for connection of an optional external control or safety shutdown device,
such as a pressure or temperature limit switch. J1 is shorted to shut down
waveform generation. For normal operation, J1 is left open.

J2 and J3 are for optional voltage modification support. For normal operation,
both J2 and J3 are shorted with 2 position jumper shorting blocks.

J4 is for the connection of optional auxillary inputs. For normal operation,
nothing is connected to J4. J4 can also be used to connect an oscilloscope
to view PWM generator waveforms on channels 1, 2, and 3.

SW1 is for disabling PWM generator channels 1, 2, and 3 via switches 1, 2,
and 3. Switch 4 is a master disable that turns off all 3 channels. For normal
operation, all 4 switches are switched OFF.

TB1 has 4 connections as follows;

DC Input + is connected to the 13.8 VDC power supply positive connection via
a 2 amp fuse or circuit breaker.

DC Input - is connected to the 13.8 VDC power supply negative connection. If
a shorting plug is installed at J3, this wire is optional.

Ground is connected to the 13.8 VDC power supply negative connection via heavy
guage wire. There are two wire connection terminals available so that two equal
length wires may be used to lower wire resistance losses.

TB2 has 4 connections as follows;

Output 1 is connected to the cold side of primary 1.
Output 2 is connected to the cold side of primary 2.
Output 3 is connected to the cold side of primary 3.
Gate + is not normally connected when a shorting plug is installed at j2.

The hot sides of primaries 1, 2, and 3 are brought together, and connected to
the 13.8 VDC power supply positive connection via heavy guage wire and a 60
amp fuse or DC circuit breaker.

Note: These fuses are for short circuit protection, not as an indication of
system power consumption.

Preliminary Test/Tune Information

DO NOT connect the PWM3F outputs to a powered transformer until after the unit
tests as fully functional. You may pull the 60 amp fuse or trip the DC circuit
breaker while testing and tuning.

Functionality Testing

Power up the PWM3F and check the indicator LEDs for proper operation.

I8 = 8 volt supply - should be lit in normal operation, off if powered down.
I7 = 12 volt supply - should be lit in normal operation, off if powered down.
I6 = PWM channel 3 disable - should be off in normal operation, on if disabled.
I5 = PWM channel 2 disable - should be off in normal operation, on if disabled.
I4 = PWM channel 1 disable - should be off in normal operation, on if disabled.
I3 = Channel 3 output - should be lit in normal operation, off if disabled.
I2 = Channel 2 output - should be lit in normal operation, off if disabled.
I1 = Channel 1 output - should be lit in normal operation, off if disabled.

If all indicators check out, then continue to tuning. If everything checks out
ok except the output indicators, then try tuning first then retest. Failures
may indicate component or soldering problems.

Preliminary Tuning

Adjust all 3 of the "DC" marked (Duty Cycle) potentiometers (R25, R27, R29)
fully clockwise, for minimum pulse width.

Connect a frequency counter or oscilloscope to J4 pin 1 (Aux Input 3) and adjust
the channel 3 "Hz" marked potentiometer (R28) for a reading of 10.7 Khz.

Connect a frequency counter or oscilloscope to J4 pin 2 (Aux Input 2) and adjust
the channel 2 "Hz" marked potentiometer (R26) for a reading of 21.4 Khz.

Connect a frequency counter or oscilloscope to J4 pin 3 (Aux Input 1) and adjust
the channel 1 "Hz" marked potentiometer (R24) for a reading of 42.8 Khz.

Note: If channel 1 shuts down while tuning towards 42.8 Khz, replace U1 with a
different brand of NE556 type timer chip. Many of these chips, like those marked
as made in tiawan, do not fully meet the NE555 spec and will shut down with the
output turned on solid. If this occurs while loaded, the output FET for that
channel may be quickly destroyed. The Texas Instruments 556 chips marked as made
in Malaysia have typically been tested to work ok at up to 45 Khz.

Once tuned, verify output at the TB2 Outputs with an oscilloscope. Without a
transformer connected, the indicator LEDs only lightly load the FETs, but enough
to verify operation during testing. If all checks out ok up to this point, you
should be ready to connect the transformer primaries and apply power.

Note: If you experience heating issues with any of the MOVs M1, M2, and M3, they
may be safely removed and left out, or replaced with slightly higher voltage MOVs.
There have been some MOVs that work properly, and some that do not. It seems to
be a batch related issue.