TROUBLE SHOOTING PRINTRONIX CIRCUIT BREAKER TRIPPING FOR Printronix 600 LINE PER MINUTE PRINTERS 

Applies to P600,600XQ,6080,6280

WARNING: THE CIRCUIT BREAKER IS A PROTECTIVE DEVICE DESIGNED TO PROTECT THE TECHNICIAN IN THE EVENT OF A POTENTIALLY DANGEROUS SITUATION. UNDER NO CIRCUMSTANCES SHOULD J16 ON THE POWER SUPPLY PCBA BE DISCONNECTED TO TROUBLESHOOT CIRCUIT BREAKER RELATED PROBLEMS.

MEASURE +36VDC AT F3 ON THE POWER SUPPLY PCBA. IF IT IS HIGHER THAN +37.5VDC THE PROBLEM IS MOST LIKELY THE POWER SUPPLY PCBA.

PRESS THE FORM FEED BUTTON ON THE PANEL. IF THE BREAKER TRIPS WHILE FEEDING PAPER THE PROBLEM IS MOST LIKELY THE POWER SUPPLY PCBA AND POSSIBLY THE PAPER FEED MOTOR.

PUT THE PRINTER ONLINE, FOR P6000 PRINTERS DATA MAY NEED TO BE SENT FROM THE HOST, TO MAKE THE SHUTTLE MOTOR MOVE. IF THE MOTOR DOES NOT MOVE, THE PROBLEM MAY BE WITH THE AC INPUT TO THE MOTOR BY THE RIBBON CONTROL PCBA J2 (ON P600) OR THE START MOTOR RELAY.

IF AFTER REPLACING THE ABOVE PARTS THE BREAKER CONTINUES TO TRIP, THERE MAY BE A PROBLEM WITH THE LOADS ON THE +36VDC. DISCONNECT THE LOADS TO ISOLATE THE PROBLEM.

The following information provides more in depth troubleshooting.

There are three states that the printer will be in at any one time. The first is the load buffer state, where information from the host system is loaded into the printer buffer. The second state is the print state, where the printer puts the dots on the paper. The third state is the paper feed state, where the paper moves vertically through the printer. The circuit breaker may trip during any of these states. There are also additional functions that may impact the circuit breaker tripping. The following information should be of assistance in isolating circuit breaker related problems.

The circuit breaker is designed to trip if the 36VDC exceeds approximately 37.5 VDC. An unfiltered 36VAC from bridge rectifier one (BR1) is used to develop + 36VDC and + 70VDC. The +36 VDC passes through a filter network (R1 and C1). This filtered + 36VDC powers the hammerbank, the hammer driver PCBA, the ribbon drive assembly, and is also passed along the backplane connector J2-4. The + 70 VDC is passed on to the paper feed circuit.

Considering the above information, the first step is to determine when the problem occurs.

1) STATIC TEST. Does the problem occur when the printer is first powered on ? If so, power down the printer (turn off the AC and unplug the power cord), then disconnect the + 36VDC loads. Remove the logic PCBA’s from the card cage and disconnect the shuttle harness from the C1 (large electrolytic) capacitor. Check for voltage to ground shorts. With the multimeter on OHMS insure there are at least 200 OHMS measured between ground and + 5, +/- 36, +/- 12 VDC. These voltages are measured at the middle edge connector (J2). The component side of the logic PCBA’s will be the even numbers, the solder side will be the odd numbers. J2-1 and J2-19 are +5, J2-4 is +36, J2-18 is -36 VDC. Once it is confirmed that there are no voltage shorts on the logic PCBA’s, move to the shuttle harness and insure the cables are not cut or frayed. When checking the harness, the meter should read an open between ground and the +36VDC line. After the logic PCBA’s and harness have been checked, the contacts should be cleaned to reduce voltage drop. And all connectors in the printer should be cleaned and inspected for tightness.

WARNING: DO NOT DISCONNECT J-16 FROM THE POWER SUPPLY PCBA or the C1 capacitor may EXPLODE!

The following is a method of checking the bulk supply voltage inputs to the power supply regulator card.

These are the voltages that should be at the bulk supply connector without any load. You are checking the input voltages to the power supply regulator PCBA. Disconnect the following connectors and check for these voltages: J12 ground (black) , J6 +10.5 (yellow) , J13 -34.5 (violet) , J9 +10 (green) , J11 +28 (red) , J15 +28 (red) , J10 +10 VDC. If any of these voltages are off by more than +/- 10% there is more than likely a problem with the bulk supply. But , that still does not completely eliminate any part that loads the supply. If the voltages are correct, turn off power and using the above information check the power supply regulator PCBA for voltage to ground shorts. Once that has been checked, reconnect the bulk supply harness to the power supply PCBA, power on the printer without the logic PCBA’s in the cage. Check to see if the breaker trips without the logic load, and also check the fault LED’s. If there are any LED’s lit, power down the printer and insure all the connectors have been installed correctly. If the problem persists or if the breaker trips the problem is most likely the bulk supply. Next check the fuses on the power supply PCBA for the proper voltages. F1 +9.5, F2 -36, F3 +36vdc. If these voltages are correct, power down the printer, connect the J2 connector between the regulator PCBA and the card cage and install the PCBA’s into the card cage one at a time, and power on the printer to see if the breaker trips. After installing any PCBA if the breaker trips, that PCBA becomes suspect. Replace it.

2) PAPER FEED TEST. The paper feed circuit is driven by the two phase paper feed signals PF1and PF2.+70VDC developed by filter R4 and C4, provides the power to drive the paper feed motor. Press the top of form button to check the paper feed function. If the printer trips during paper feed, stop, disconnect the paper feed motor and check the impedance of the four paper feed motor windings (about 3 ohms increasing to infinity as the shaft is rotated) measure across the first and second windings on the left side of the paper feed motor connector, then measure across the third and fourth windings on the right side of the connector. If the windings check okay, the bulk supply or the power supply PCBA is probably bad.

3) SHUTTLE TEST. If the paper feed function checks, put the printer on line, and send data to the printer in the case of 6xx0 printer and check that the shuttle moves, comes up to speed, and stops. If there is a malfunction in the shuttle circuitry that causes the breaker to trip, check for 110 VAC at TB2 -1 TO TB2 -8 (START WINDING). If there is no AC at the TB2 test points, check for +5 VDC at the front of the motor start relay pins 3 and 4 ( small gauge red and black wires). This solid state relay is actuated to apply AC line voltage to the start winding of the shuttle motor. When the printer is put online, the signal NSD ( shuttle detect not) releases the clock counter and dual flip-flop, which allows the +5vdc to be sent to the solid state relay. The MPU (magnetic pickup) counts the number of rotations by the flywheel. After the flywheel has rotated the appropriate amount of turns in the appropriate amount of time, the logic determines that the shuttle motor is up to speed and the printer comes ready. If the MPU circuit does not detect the proper amount of pulses in the proper amount of time, the breaker will trip. Check the MPU gap (.010"), check the MPU signal at the power supply PCBA J4-2 (sync 2.0 to 3.5 Vp-p, resync 4.0 to 6.0 Vp-p), check the MPU impedance (650 to 740 ohms).