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Phantom Pages On The 4500

18 Jul, 2001 By: Steve Geishirt imageSource

Phantom Pages On The 4500

Suddenly, like clock work, our tech support started getting calls on some pretty strange symptoms. We had about four or five different technicians call over a week’s time complaining about their customers’ 4500 printers, looking for solutions to something really bizarre. The symptoms were closely similar; the printer warmed up fine, and when a print job was sent, it took the data and began to print. However, the printer would then spit out a blank page, hesitate for a second, and repeat this process until the paper tray was empty. This was also the case if an engine test was requested. The symptoms remained the same even with the formatter PCA removed from the printer and after performing a factory default cold reset. There was also no error code produced.

ITB Theory

Customers who knew their troubleshooting did a stop test to look for an image on the transfer belt, but found none. They also tried a stop test to look for an image on the image drum but again found none; we assumed they timed this test right, as it is a tough one to get. We had technicians watch the timing marks on the two white gears on the left side of the printer to see if the transfer belt was being raised to the image drum, which it was.

We suggested technicians run some of the internal diagnostics tests with the ITB drawer removed to watch and verify all was working well. When they tried the developer test, the carousel revolved around and kicked the toner cartridges one by one toward the image drum as it was supposed to. The drum test rotated the image drum and allowed a clear view of the lift levers lifting as if the ITB was in place. The sensor tests verified all sensors that were accessible were working. Customers began shot gunning by replacing the DC controller, the Formatter PCA, the ITB drawer, the paper cassette tray 2,the laser scanner, and the high voltage power supply. All of these replacements resulted in the same symptoms. Then a customer replaced the ITB unit, or transfer belt, and the printer started acting normal again. We started looking at the wiring diagrams of the 4500 manual to investigate the connections to the ITB and realized that one logic contact went directly to a photo sensor that sensed the home position of the ITB belt. How could a photo sensor cause a printer to do this?

Photo Sensor Theory

Then a printer was sent to us by one of the technicians who had had enough! Our printer repair department began working on it before I knew it was in the shop, but once I found out it didn’t take me long to go take a look at it. Printer repair had already run an engine test with the formatter removed and replaced the DC controller with no results. I began engine diagnostics looking for clues thinking “I’ve run these tests a thousand times in training, so I know what I’m supposed to see; perhaps the others are missing something!” Nothing out of the ordinary was found. Bill Voelker, one of my trainers, also stopped by and suggested we replace the ITB unit with one from our training machines. I thought that it was worth a shot and as he went to get it, I checked the ITB maintenance count in the service menu. Strangely enough, the maintenance count was higher than the total page count of the printer. I decided to change the transfer life count by setting it below the total page count to see if this created some sort of conflict with the internal logic, but I saw no change. Bill returned with an ITB unit and upon placing it in the printer it spit out a nice clean configuration page with all the colors in the right places. We both looked at each other in amazement and agreed we needed to run this ITB in another printer. We took it to a 4550 and it ran fine with no problems; however, when we returned it to the 4500, the printer returned to printing blank pages repeatedly.

Upon checking the serial number of the failing printer, we found that it was a first revision 4500 printer. Since we knew there were two versions of the 4500, and the 4550 basically worked of the second version engine, we thought there might be a connection between the firmware of the first revision engine and this ITB belt problem. Our other first revision printers were being sent to New Jersey as we were dovetailing training to the Exposition East show in a couple of weeks so we could not try this ITB unit in one of them.

Since we had the ITB, we double-checked the connections to the unit, verifying that the only thing the connector went only to the photo sensor. With all the toner on the unit, I thought we could try to fix it by using compressed air to blow out the built up toner in the photo sensor in case that was the problem. Bill went to blow out the toner then reported the printer was now “printing.” We began to theorize what was taking place here and Bill told me that when the printer first came in, it did print out a configuration test or two before going to this “no print, empty the tray mode.” In other words, once it warmed up it started spitting out these blank pages. We tore apart the photo sensor on the ITB unit and drew out the schematics hoping to find something unique, but it looked like most other photo sensor circuits. Uncertain as to what was going on, we came up with a couple of theories regarding possible photo sensor related causes.

One theory was that toner build up on the photo sensor had just gotten to the point that one of the two home position notches cut into the ITB belt was seen, but the other may not have been. This second missing notch could have created confusion in the program of the firmware on the DC controller. Instead of supplying an error code, the printer got caught in a continual loop of knowing it erred, but wasn’t directed to create an error code to stop the process, so it tried again and again. The problem with this theory is that the unit worked in the 4550 without an error code. Even if they fixed the problem in the firmware, why would no error code be produced?

Excess Current Theory

Another theory was based on excess current being drawn due to toner build up on the photo sensor once the printer was warmed up. This increase in current then decreased the positive 5 Volt line the photo sensor was using. This decrease did not effect warm up, but it only came into play when all the parts were working together via the printing process. The combination of toner build up and decreased voltage was just enough to create confusion in the firmware and send it into its continued loop of print attempts. However, this theory was also shot down the next day when Bill reinstalled the belt into the previously failing printer (after it had set powered off all night) only to see the belt fail again.

ITB Solution

Our theories went on and on from suggesting an increased resistance of the driving of the belt which affected the drive motor, to theories of either the transfer belt charge, or cleaning roller charge and how they were zapping the photo sensor, thus zapping the DC controller. Perhaps it was a bad batch of ITB units? Why did so many of these printers suddenly crop up with such a similar error with replacement of the ITB unit being the solution in all cases? To this day, we are still searching for the “exact” cause, but what I can tell you is if you come across a customer with a 4500 printer with these strange symptoms, replacing the ITB belt does fix it. I thought it more important to publish this article without all the research done so you can fix your customers’ printers and be their hero even if you do not know exactly why it is failing.

In a final note, since our initial tests, we did locate another first revision 4500 printer and attempted to recreate the error using the bad ITB unit. The printer ran all day without failure.

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