Lionel CW-80 Transformer General Description “Original Version”

Also consult the Lionel Owner’s Manual at http://www.lionel.com/media/servicedocuments/71-4198-251.pdf

This description covers the “original” version of the CW-80 transformer. This version had several problems that were subsequently modified in the “revised” version covered elsewhere. Some photos used here are from a revised unit.

The CW-80 transformer provides one variable output for running a train, and a second programmable output for powering accessories. Pushbutton controls are provided for Direction, Horn/Whistle and Bell.

Basic power circuits

The basis of the unit is a fixed-voltage transformer that has an open-circuit output voltage of 17.9 volts AC. The transformer is quite hefty, weighing 4.5 pounds. The equivalent series impedance at the output is approximately .15 ohms. The transformer is protected by an internal fuse embedded in the primary winding, connected in series with the primary winding.

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The two transformer output leads are connected through two wires to the controller printed circuit board. The Return side of the transformer connects directly to the circuit board, while the Hot side passes through an 8-amp slow-blow fuse encased in shrink

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tubing. The wire leads to the fuse are soldered directly to tips on the ends of the fuse. After passing through the fuse, the Hot side connects to a junction point on the PC board that feeds red wires to the “A” and “B” terminal.

NOTE: Unlike most older Lionel non-electronic transformers, the “original” CW-80 does not use the “U” terminals as a commoned Return connection that ties to the common reference of the layout. The transformer Return wire feeds the Ground reference of the logic circuits, but it does not connect at all to the “U” terminals on the back of the transformer. In fact, for this transformer, the “U” terminals aren’t even connected together! It is the “A” and “B” terminals that are tied together to the Hot side of the transformer. The two Red terminals are tied together internally, and the two Black “U” terminals are the independently-controlled leads. In electronic terminology, these are “pull down” outputs since the control Triacs short the Black terminals to the Return side of the transformer. (The Lionel PowerMaster and TPC300/400 are pull up devices.)

The black “U” terminals each have black wires that connect to the respective Track and Accessory Triac power controllers on the PC board. The combined current from the 2

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Triacs passes through a current sensing ‘resistor’ composed of a 2.8” length of #18 nickel-alloy wire, then to the Return wire to the transformer. The voltage drop created by the combined current flowing through the wire resistor, referenced to Logic/Analog ground, is applied to a non-inverting opamp to boost the signal. Only the positive half of the waveform is amplified, with the negative half sliced off by a Schottky diode connected in shunt across the opamp’s non-inverting input terminal.

The Hot connection on the PC board splits to drive

1. A regulated +5V power supply,

2. The red (+) lead of a small 12VDC fan and

3. One input of the microcontroller as a synchronizing reference to the AC power waveform.

1. The black lead of the fan is connected thru a diode to the transformer Return point. As a result, the fan is driven with halfwave DC derived directly from the 18V AC input from the transformer, resulting in an effective DC voltage to the fan is 9 volts. Although running a fan on 3/4ths of its rated voltage reduces fan noise, it also cuts the airflow by the cube of the voltage. In this case, the airflow is reduced to about 42% of the rated value. Reduced voltage may also create starting problems when the fan ages and the bearing bushings offer more friction.

The fan diode marking on the board is backwards compared to the way the fan diode is installed. The marked direction would run the fan off the negative half cycle of the AC waveform, which would actually help to minimize the DC component of the current in the core. The disadvantage is that the black lead from the fan would need to be attached to the red Hot lead coming from the transformer.)

2. The +5V logic power supply is a simple half-wave circuit referenced to the transformer Return side. A 78L05 regulator provides a constant voltage for the microcontroller (uC), control handle potentiometer and the current sensing circuit. The +5V output has one large electrolytic bypass capacitor and 3 smaller capacitors located near the various load points. A reverse bias protection diode is included from the regulators output to input pins.

3. For phase control, the microcontroller must know when the AC sinewave cycle begins. A simple 10K ohm resistor from the Hot side of the transformer feeds one uC input to provide this information. Noise is filtered out by a 2200 pF capacitor from the uC pin to ground. The input to the uC is clamped by two diodes in a single package, one diode clipping the input at one diode drop above the +5V rail, and the other clipping at one diode drop below 0V ground reference.

Track and Accessory control

A lever handle is used to control the track voltage and to program the fixed Accessory voltage. The control handle moves a 250 Kohm rotary potentiometer that has +5V and

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ground at its end points. A secondary 2 megohm trimmer pot is connected from the control potentiometer wiper to the +5V end. The potentiometer has a normal rotation range of about 300 degrees, but the lever only swings through a limited portion of this total range. As a result, the output voltage ranges from zero to 3.3 volts.

NOTE: The output voltage of the potentiometer is connected backwards to the normally expected “OFF is zero volts, and full ON is max positive volts.” In this case, the OFF condition is actually set by the 3.3 volt maximum voltage from the wiper, and full ON is set by zero volts at the wipers output. This means that the potentiometer’s output voltage when the lever is OFF must be the expected voltage that the uC has been programmed to expect for OFF. The secondary trimmer pot provides a small range of adjustability to accommodate variations in the potentiometer’s output. The control potentiometer is connected to the PC board via a 3-pin connector, facilitating potentiometer replacement if and when the resistive element or wiper in the potentiometer wears out.

The potentiometer’s wiper output feeds an analog-to-digital (A/D) input on the uC, permitting the controller to respond to the position of the control handle. The A/D converter provides 256 steps from zero to +5 volts, but the restricted range of the potentiometer utilizes only 169 counts of this full range.

Two Triacs provide variable phase control to adjust the effective output voltages of the Track and Accessory terminals. A series RC circuit fed by the appropriate output pin on the microcontroller triggers the gate of each Triac. A single pulse on the gate of the Triac triggers low voltages. As the voltage increases, extra pulses are added onto the leading edge of the gate trigger signal at 300 us. intervals.

Each of the Triacs is bypassed by a resistor and capacitor in series to reduce transients across the Triacs. NOTE: These rather large 1 uF capacitors will cause misleading output voltage readings on a high-impedance digital voltmeter if there is little or no resistance connected from A or B to U at the output. The impedance of the capacitor, even with the Triac shut off, will be much lower than the input impedance of the digital voltmeter, causing virtually the entire available 18 VAC to appear across the meter. When testing this transformer, add a light bulb across the output being tested. The bulb will not only offer a low resistance shunt to help the meter read correctly, but it will also give a visual indication of what is happening with the output voltage as the lever is changed or the Accessory voltage is programmed.

The microcontroller is a Motorola MC68HC908JK3CP, a general-purpose controller with Input/Output pins that can be utilized as either logic pins or A/D converter input pins. An external 29.4 MHz crystal and associated capacitors and resistor control the clock frequency of the uC.

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Three of the uC pins service the 3 control pushbuttons (which pull down to ground when pressed), 2 pins provide trigger signals for the Triacs, 1 pin controls the green LED, 1 pin monitors the control potentiometer’s wiper voltage, and 1 pin monitors the output of the current sensing circuit. In addition, unused pins are wired to unstuffed/unused 2-pin and 6-pin connectors that appear to be provisions for derivative versions with additional functionality.

The current sensing circuit sees an input voltage of about 310 millivolts on the peak of the sinewave at about 5 amps total current. This signal is amplified to 2.36 V by the opamp. The 8-bit A/D encoder has a step size of 19.5 mV/step, which means that an overload would be a count of about 121 at the encoder’s output. (Maybe “Overload” is detected when the 8th bit changes at the 127-to-128 transition?)

The “Direction” control button interrupts power to permit cycling of the locomotive’s direction control device. When the button is released, the power is ramped up over a period of 3 seconds, providing a gradual start.

The “Whistle/Horn” button injects a positive DC signal into the track voltage by slightly lengthening the positive half cycle and shortening the negative half cycle. The response to a button press is immediate.

The “Bell” button injects a negative DC component by interchanging the lengthening and shortening to the opposite half cycles. The button has a delayed latching response, requiring the button to be held for a minimum of 3 seconds to either engage or disengage the Bell function.

The output voltage on the Accessory terminal can be programmed to voltages at or below the available 18V maximum. Follow the directions listed in the owner’s manual for programming. Note that the programming isn’t complete until the control lever is returned to the OFF position. Also, when the lever hits OFF, the Accessory output will momentarily jump to full output, and then assume the desired reduced output.

Opening the case

The screws that hold the case together are “tamperproof” screws with a triangular head.

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Although special tools are available to fit this head, a straight-bladed screwdriver of the appropriate size will also lock into one edge of the triangle. The screwdriver shown in the above photo has a tip width of 1/8” (.125”).

Observations:

There are no transient suppressor components.

The air slots for air intake and exhaust are extremely small, probably restricting the circulation of fresh air through the unit.

The power transformer is quite hefty compared to Lionel’s earlier non-electronic transformers.

The use of pull down output prohibits the use of accessories that must be connected to track common, such as 022 switches, cattle and horse corrals and Lionel uncouple/unload tracks.

Lionel CW-80 Transformer Troubleshooting

Symptom Procedure

No LED/lights or fan Check AC outlet and cord

Blown fuse

Check primary winding resistance

Resistance between AC plug prongs should be about 3 ohms

LED but no fan Fan stuck or burned out

Measure voltage across fan red and black wires. Should be slightly less than 9V.

(12V fan may not be dependable at 9V.)

LED and fan OK, but:

No output on “A” Terminal A/D input to uC pin 6 at 3.3V or higher

Control potentiometer top leg disconnected – end with yellow wire

Pot wiper not making contact – white wire

Bad connection at 3-pin connector

Current limiting locked – LED should flash

Bad op amp with output stuck high – +5V on uC pin16

Current sense resistor resistance high due to bad solder connection

No AC sync signal on uC pin 18

uC dead

Oscillator not functioning – should have 30 MHz on pin 3

Bad uC chip

Check +5V on pins 5 and 20, ground on 2

No Accessory “B” output Can’t program fixed output because A/D input on uC pin 6 is 3.3V or higher (see above)

Full output only on Accessory output Triac shorted

Measure resistance between “A” and “U” – should be very high resistance, but on high resistance meter ranges there may be lower readings while the Triac’s bypass capacitor is charging. Wait until reading stabilizes.

A/D input to uC pin 6 at or near 0V

Control potentiometer bottom leg disconnected – end with yellow wire

Pot wiper not making contact – white wire

Bad connection at 3-pin connector

Accessory “B” voltage always full output Triac shorted

Measure resistance between “B” and “U” – see above

Unable to program Accessory voltage Programming won’t work if one of the buttons doesn’t close (faulty switch)

Does LED begin flashing after you press all 3 buttons simultaneously?

Voltage isn’t really locked in until control lever is returned to cutoff position, at

which time the output will spike to full voltage, then settle back to the

programmed value.

Horn or Bell activates continuously or Stuck switch – measure resistance across switch

No Reverse function

Power doesn’t shut off fully when handle is OFF Potentiometer wiper voltage isn’t going to high enough voltage. Adjust or add trimmer

from yellow wire to white wire on potentiometer.

Voltage jumps around during operation Potentiometer wiper making intermittent or poor contact

Dirty track

Loose connections

Sporadic bell or horn ?

Operator Errors

Bell button doesn’t work Bell button must be held closed for 3 seconds to activate the Bell circuit

Transformer output doesn’t respond quickly Normal operation – transformer ramps the track voltage up over a 3-second period when

after Direction button is pushed Direction button is released

Notes:

1. “uC” is microcontroller chip

2. All voltages measured with respect to Ground. Attach ground clip for meter to banded end (closer to fan) of large diode next to

LED.

3. Do not measure output AC voltages with voltmeter unless a loading resistor is also connected across the output. A light bulb makes a good loading resistor since it also gives a visual indication of output voltage. Failure to use a loading resistor will result in measurements that will indicate full output voltage even when the Triac is really shut off.

4. Adjustment potentiometer voltage is ‘backwards’, with zero volts on wiper producing full output, and 3.3V on wiper shutting off the power.

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