Laserjet 9000. Second duplex page full of "bubbles", black area on the bottom

[printer]

I have two issues:

First Issue: The first page of the duplex page is fine. On the second page there are always "bubbles" on the print, it looks like the paper went a bit through water. If I print without duplex, the print is OK.

Second issue: On the end of each page there is a black area. I don't know why it is there, and it mostly appears only beginning from the fourth page that is printed.

I really like this printer, but it is so hard to figure the problems out, I am trying to solve both issues since a half month and I spend so much hours in solving them, but without any success so far

[cs_steve]

Could be faulty toner cartridge (most likely) , faulty transfer roller, or faulty high voltage power supply

If you have a spare cartridge I would insert that and see if the problem goes away.

If that doesn't help I would change the transfer roller, as it's easy to do and less expensive than the high voltage power supply.

Finally, high voltage power supply.

[printer]

Thanks, Steve. I already bought three (!) additional transfer rollers, so I don't think it is because of that.

That is a DC controller, can you help me out there?

[cs_steve]

Sorry, not DC controller, I meant high voltage power supply... (changed my post above)
This component distributes the voltage to various components like toner cartridge, laser scanner -- if High Voltage Power Supply sends the wrong voltage, you can get that bubble print.

Are those transfer rollers genuine HP brand or aftermarket? If they are not genuine HP, then they could still be doing this. We've seen bad aftermarket brand transfer rollers give horrible print quality specifically on duplex print jobs. You can get all kinds of strange print, specifically the black print you mentioned at the bottom of each page, etc.

You didn't mention toner cartridge -- like I said, that is by far the most likely cause... so if you haven't swapped that, I would try it as well.

[printer]

The transfer rollers were OEM from two different manufacturers.

I tried a XEROX toner and a OEM toner and the same two strange problems ("wet look" + black area on the bottom) appear with both of them.

Can I put a Laserjet JLMFP 9000 power supply into the Laserjet DN 9050?

I really am thinking of just buying another Laserjet 9050 but it would be a pity.

[cs_steve]

The High Voltage is the same for 9000 & 9050, so yes they are interchangeable.

[ptjeff1]

The transfer rollers were OEM from two different manufacturers.

FYI there is only one OEM -- HP. Most aftermarket transfer rollers for these models are notorious for poor print quality when duplexing.