Common PO6-250 / 251 Faults in the Xerox Docutech

In the years that I have been writing this column, there have been quite a few technicians that have contributed information in one way or another. Some by submitting their repair solutions and others by asking for a suggestion for a fix for their immediate problems. As most of you know, if I didn’t have an immediate answer for you, I would always get back to you with some sort of resolution to the problem. I’m a firm believer in documentation and if you don’t have the proper tools, it would be almost impossible to troubleshoot or remedy a system fault in the Docutech or any copier for that matter. I certainly have to hand it to some of the techs that have called me with specific problems knowing that they did not have the proper documentation or tools. A true technician is the guy / gal that dives into a problem regardless if they are properly prepared or armed with the latest documentation. To those guys and gals I tilt my hat to them.

PO6-250 – 251 system faults have terrorized many technicians and customers for as long as the Docutech has been in service. The PO6-250 system fault tells us that the SOS PWB did not detect the start of scan. Or if you get a PO6-251 system fault, it means that the EOS PWB did not detect the end of scan. Keep in mind that the EOS and SOS PWB’s are quite resilient and usually do not fail easily. If the PWB’s are suspected, you can swap them out or try a slave PWB if you have one in inventory. 99 times out of 100 the PWB’s are good.

Check MIN NVM values first and make sure that in MIN location 152, the value must be 60, and in MIN location 153, the value should be 85. Keep that in mind when the values do change, and they often change for a reason. The Docutech NP-135, 6100, 6135 and the 6180 are extremely sensitive to ‘NOISE’. And as everyone knows, almost any electrical device can generate a noise. The electrical device could be almost anything that uses electricity: motors, solenoids, and switches; a bad ground strap in the fuser metering tray or the ground strap in the bindexer assembly could also contribute to the noise problem.

When you enter diagnostics, look at the last 50 shutdowns. Have you noticed any PO9-201’s? A bad Dicorotron emitting noise can trigger all kinds of failures in the MIN NVM settings. If you notice in the last 50-shutdown screen that there were many PO9-201 shutdowns, it could be due to an arcing Dicorotron assembly. Use dC-910 to eliminate any bad Dicorotrons or just replace them all.

Check the lamp in the laser tube for a glowing light. Is the laser tube lamp glowing steady? This lamp should never blink or flicker. Cover the photoreceptor belt with white (11”x22”) paper directly under the ROS assembly. Cheat the processor interlock bypass switch and enter dC-330. Select [6] and then select [laser write]. Press the ‘Start Print’ switch (to activate the command). Kneel down on the floor, as if to say your evening prayers, and observe the laser line on the white paper. It should be the same density from the front to the rear of the machine. If the line is the same density from the outboard end to the inboard end then we can assume the laser is doing its thing. If you swapped out the EOS PWB with the SOS PWB, return them to their original positions. Otherwise you will have to perform the ROS magnification set up.

NOTE: if after swapping the SOS and EOS PWB’s you notice that the line is dim on one side and when you swap the PWB’s back, the line is dim on the opposite side, it could be that the PWB is bad and should be replaced. Otherwise continue your troubleshooting. Make sure that when you are using diagnostics to toggle the ROS assembly on and off there is no electrical noise coming from any of the machines motors except the Polygon motor. For all intents and purposes, the Docutech is in standby and if an electrical device (e.g., a motor) is causing the noise you will not see it happen. However when the Docutech is under a load and all electrical devices are energized and doing their assigned tasks, a noise will be generated and will cause the PO6-250 / 251 to happen.

A technician reported that he had a intermittent PO6-250 system fault that happened on rare occasions. It happened only when they were running a special job for an insurance company. After careful investigation and troubleshooting, it was traced to the #2 paper tray as it supplied slip-sheets to the job. The PO6-250 would be declared (intermittently) when the Docutech would use the colored paper in tray #2. It wasn’t the colored paper that caused the problem but it was the clutch that was emanating the noise that would (sometimes) generate enough noise to shut down the system with a PO6-250.

Another situation that produced PO6-250’s was traced back to the metering tray (RAM tray). Someone eliminated the ground strap and did not think it was important to replace or repair it at the time. While we are on the ground strap issue, check to see if the Bindexer door is properly grounded to the frame of the Bindexer assembly. Static electricity can cause some weird phenomena.

Replace the two relays inside the Low Voltage Power supply if the contacts are pitted. Or even if they are not pitted or contaminated, it is a wise decision to just plain replace them. Relay K104 and K103, and supply 24 volts and 34 volts to the interlock system. When they get old and the contacts become contaminated or pitted, they have a habit of losing voltage for a split second. As the printer gets older, you may notice it has a tendency to vibrate more than when it was new. That power interruption, however brief, will cause many problems, especially in the ROS assembly.

In a few instances, the Polygon motor was not coming up to speed quick enough and it caused a problem in the ROS assembly. How do you check that? Good question grasshopper. If you suspect the Polygon motor and you have another ROS assembly, try swapping it out with another printer. If the Polygon motor assembly is making a loud noise, and you can hear it, that could be a sign that there is something wrong and the motor should be replaced. A technician in NYC borrowed a stethoscope from an attending physician to listen to the ROS assembly while it was in print mode. A little melodramatic I agree, but it worked and saved him from grief. I remember once when I took my car to a mechanic to have some work done, the mechanic had the handle of a screwdriver close to his ear and the tip on the motor block, listening to the engine. The guy diagnosed the problem in a heartbeat and problem was not as bad as I thought it would be. I’m not sure if using the screwdriver trick on the ROS assembly can even be done safely and should not be tried.

Whenever we run into intermittent problems, we sometimes blame the situation on “THE SOFTWARE”. In my experiences with working on the Docutech family of printers for over twenty-five years, I have never come across a situation where the software was the problem. So, by reloading the software, that won’t resolve the problem. Never reload any software in the Docutech printer unless the RAP leads you there. If and when the RAP says to re-load the software, make sure you have the latest version of the software and the installation instructions available and a note from your mom giving you permission to do this.

Noise can also be generated by loose connections as well. The next time you get behind the Docutech printer, disconnect the power cord and sit down on the floor behind the Low Voltage Power Supply. Unplug all the P/J connectors on the LVPS and inspect all the pins, both male and female. Notice if any pins are fretted from vibrations. Is there any apparent rust or pitting? Now would be a good time to replace any pins with the gold tip retrofit kit Xerox has on sale. While you are sitting on the floor, open the AC panel and let it drop to the floor. Disconnect all the Plugs and Jacks on the AC panel and closely examine the pins, both male and female, to see if there are any burnt or damaged pins. It has been my observation that fretting has occurred to many pins on the AC panel assembly. The fretting occurs due to the machine vibration when the machine is running. There is no way this can be prevented because as the machine ages the vibrations will usually get worse. And that’s because the Docutech is aging and everything is getting loose.

Install the plug and power up the Docutech NP-135 and wait until it’s in the ready state. Have your handy dandy meter ready and check all the connectors on the back of the Low Voltage Power Supply one at a time. Use the BSD’s to determine which P/J’s supply the Low Voltage, especially the 5 VDC lines. Check all voltages on the output side of the P/J connectors. Then check all the 24 VDC lines and the 34VDC output lines. I like to check the line voltage at the P/J connector because this is the voltage the machine actually gets. The 5VDC power is used by all the PWB’s for its DC power, and if the voltage drops below 5VDC, you can expect big problems. If you check voltage on the terminal strip on the bottom of the Low Voltage Power Supply you will (usually) get the correct voltages, but that is not the actual voltage that is being delivered to the various components and therefore is not really a good place to check for the actual 5 VDC.

Inspect the toner dispenser interlock (in the back of the printer). On one rare occasion I discovered that the interlock was loose and was causing the PO6-250 problem. The interlock is there so that we can’t open the belt module while the Docutech is in print. Somehow I can’t imagine why anyone would want to open the Belt module while the printer is in print, but who am I to second-guess another tech. While we are on the subject of the belt module, make sure it’s not vibrating and (maybe) opening while in print. The Toner dispenser interlock could be barely making a solid connection in the back. There is a way to file the plastic housing on the connector so that it goes a little deeper into the frame. Even if you are only able to file off a 1/16 inch, it may help by making a better connection.

Another component to check is the idler rollers on the top transport assembly. They have been known to emanate noise while the machine is running. Make sure they are all properly grounded to the frame. In my travels I have also seen cleaner assemblies that have become somewhat compacted with toner emit a noise problem. After removing the cleaner assembly and dismantling it for a thorough cleaning and de-toner roller inspection, can you actually see if the cleaner was the problem? Paper tray 3 interlock switch was the cause of one printer to experience a PO6-250. Hey, any paper tray interlock could contribute to the problem; it is rare but it is something you should be aware of. Paper tray motors have been mentioned in bulletins from field engineering that they could generate a noise problem as well. Also check the two P/J connectors that live on top of the developer drive motor (next to the ROS assembly) for burnt or pitted pins. Almost everyone I talk to have missed these two P/J’s and when they are examined, they were found to have several fretted pins on both sides of the P/J connector.

I hope that this article was helpful to you in resolving the PO6-250 / 251 system fault shutdown. If I missed anything, please let me know what it was so that I may insert it in the next column. I am available at VillageCopierNY@AOL.COM . Thanks for your help with this article.