HP M680dn CLJ No black line on Engine Test Page

[lane1957]

Hello Everyone! So, I have a customers HP M680dn CLJ that had a bad Main Drive Gear assembly making the usual grinding noises. I have replaced the main drive gear assembly. After reassembly, tried an engine test page print. I get no black line on the engine test page. Printed Configuration pages are completely blank. I have triple checked the main gear assembly alignment. Definitely not the problem source. Checked the lower HV board for spring contact alignment. All is good. So far I have changed out the lower HV PCB and DC Controller boards, and main formatter assembly, with known good boards. No change. Reinstalled latest firmware from a thumb drive. Using HP OEM toner cartridges and tried a couple of good black (K) cartridges. Still, no change. Checked to see if the OPC drum in the cartridge is moving during a test print. It does move. However, no toner is being applied to the black toner OPC drum. Used a multi-meter and checked all contact points from the new drive gear assembly to the HV board. All OHM out good. Used an Oscilloscope to watch DEV voltage generation to the black toner primary charging roller. Still nothing. No black toner is being applied to the OPC drum. Printer initializes perfectly with no error messages. All diagnostics via the Control Panel pass testing. Nothing in the event log except the usual half tone error codes regarding the black toner. I taped the toner cartridge contacts to see if I could get an all black page to print. Nothing...no change. Running out of ideas here. May be a faulty cable I suppose attached to the DC Controller board, or coming off of the HV board, but from the manuals I have been unable to determine how to check the signals with an Oscilloscope for the primary charge roller, or developing roller to see if there is a voltage or signal problem. Anyone have any ideas? Kind of complicated I know, but I am out of ideas....

[GIUBOSS]

before the first repair when you say "it had a bad main drive assembly which produced the usual grinding noises" did it print well?

[DRichard]

Hello Everyone! So, I have a customers HP M680dn CLJ that had a bad Main Drive Gear assembly making the usual grinding noises. I have replaced the main drive gear assembly. After reassembly, tried an engine test page print. I get no black line on the engine test page. Printed Configuration pages are completely blank. I have triple checked the main gear assembly alignment. Definitely not the problem source. Checked the lower HV board for spring contact alignment. All is good. So far I have changed out the lower HV PCB and DC Controller boards, and main formatter assembly, with known good boards. No change. Reinstalled latest firmware from a thumb drive. Using HP OEM toner cartridges and tried a couple of good black (K) cartridges. Still, no change. Checked to see if the OPC drum in the cartridge is moving during a test print. It does move. However, no toner is being applied to the black toner OPC drum. Used a multi-meter and checked all contact points from the new drive gear assembly to the HV board. All OHM out good. Used an Oscilloscope to watch DEV voltage generation to the black toner primary charging roller. Still nothing. No black toner is being applied to the OPC drum. Printer initializes perfectly with no error messages. All diagnostics via the Control Panel pass testing. Nothing in the event log except the usual half tone error codes regarding the black toner. I taped the toner cartridge contacts to see if I could get an all black page to print. Nothing...no change. Running out of ideas here. May be a faulty cable I suppose attached to the DC Controller board, or coming off of the HV board, but from the manuals I have been unable to determine how to check the signals with an Oscilloscope for the primary charge roller, or developing roller to see if there is a voltage or signal problem. Anyone have any ideas? Kind of complicated I know, but I am out of ideas....

I would suspect "Tech Lightning" has struck again. If it was printing before your repair, I wouldn't jump to defective part(s) as the culprit. I would first suspect I had goofed during the reassembly process. It wouldn't be the first time if it was me. Good luck!

[lane1957]

before the first repair when you say "it had a bad main drive assembly which produced the usual grinding noises" did it print well?

It did print fairly well, yes. Likely I messed up somewhere. I have completely disassembled it now 4 times looking for anything I missed. Used alignment pins to ensure the main gear drive cams were aligned properly.
I'm down to ohming out connector cables. Wish I had a schematic of the DC Control PCB, and lower HV PCB. Sigh....I can find nothing out of place. All appears to be as it should. "Oscope" shows the DC Bias is being
produced from the lower HV PCB to the K toner. Black toner cartridge does not pick up toner at all. OPC and charge rollers turn properly. Very weird....I will keep at it. If I find out what it is, I will post it here though. Thanks for the reply! :-)

[lane1957]

I would suspect "Tech Lightning" has struck again. If it was printing before your repair, I wouldn't jump to defective part(s) as the culprit. I would first suspect I had goofed during the reassembly process. It wouldn't be the first time if it was me. Good luck!

LOL! Well, I certainly would not rule that out. Happens to the best of us on occasion. THX for the chuckle. :-)