Waully

asked Mar 26, 2013 at 7:43pm
Hp HP LaserJet 4

HP Laserjet 4P - prints only blank pages

We have a Laserjet 4P which has taken to printing only blank pages. Whenever it has had problems in the past, I've tried to print self-test or demo pages and discovered the printer works fine, it's some sort of comm problem from the computer.

Yesterday, we tried to print a couple different pages from different applications and blank paper came out. I went thru the routine I've gone through in the past:
1) Check that LPT port is set to AT or Standard in BIOS
2) Make sure that cable is connected correctly on both ends
3) Sometimes remove and re-insert toner cartridge [had to do that today because I tried to reuse a blank page and the paper jammed]
3) Try simple page from Notepad or print from a CMD window
4) Unhook printer, restart, try printing self-test or demo page
5) Printer gets such low usage, it is nowhere near the capacity of the toner, so cartridge is presumed good.

Up until yesterday, the last few pages have printed just fine, dark across the entire page [no light text or graphics], everything sharp and crisp. Absolutely nothing on the pages now, whether printed from some application, or direct from the printer. Based on what I've read in various posts in the past, it sounds like the high voltage board may have bit the dust. If that is incorrect, please let me know. If there is a way to test, I'd appreciate how to do that as well. Thanks, Paul
How in the world does this board come out? At a glance, it appears like it's a near complete dis-assembly. Can anyone help with R&R instructions? And confirm that the high voltage board is the issue? There is no error showing on the display.

Thanks!
Paul
by Waully on Apr 2, 2013 at 9:16pm Add comment
I think it's a hardware issue. Most likely: the printer needs repair or replacement (given it's an old one already). Try it on another PC to be sure.
by Trendsetter on Apr 2, 2013 at 10:48pm Add comment
I'm certain of that; when it's disconnected from the computer [parallel cable], unplugged from the wall for a few minutes, then plugged back into the wall ONLY, it will spit out blank pages when trying to do a test page or PCL page. There are no error messages on the display. If it's the DC/High Voltage board, I'm willing to patiently wait until I find one for cheap and replace it. I found a nice replacement 6P printer for my parents with low page count for $25, so they are taken care of.

Is there a disassembly guide or a step by step to remove the board?

Thanks,
Paul
by Waully on Apr 3, 2013 at 8:53am Add comment
Try printing from the Manual Feed. It could be caused by a sticking feed roller solenoid, which is on that DC board. I've never seen the HV portion of the DC controller board on that model cause blank pages.
by moe on Apr 3, 2013 at 10:43am Add comment
Thanks Moe. I thought I'd read in the forums that HV could cause that problem, although it's possible it was a 4P post that was interspersed with 4L posts. I'll try using Manual Feed and post back.
by Waully on Apr 3, 2013 at 1:44pm Add comment
Plugged printer in, turned on, no paper in main tray. Tried to print demo page, inserted paper through manual feed slot. Nothing on page other than a tiny bit of haze on one edge. Tried it twice, same result.
by Waully on Apr 3, 2013 at 2:48pm Add comment
Other things that can cause a blank page are laser shutter not opening (that's kind of unlikely in that model). HV contacts. Transfer roller issues.
Can you get the cover off? To do so, you pop off the square box on the left and unhook the connector inside. Open the top, remove the cartridge and leave it open. Remove the 3 screws inside. Remove the paper tray and remove the one screw at the top right. Open the back door. Pry up on each bottom corner to release it. The difficulty is getting it over the power switch. Once it's off, you can check if the shutter opens when you put the cartridge in. It's just above it.
You can also check the 3 HV contacts to see if they are clean and spring up when depressed. Push down on the transfer roller on each end and see if it pops back up. If all that checks OK, then it's probably the DC controller. Everything has to come off to get it out including the fuser assy. Formatter board on the side, and the power switch. Easy when you know how.
by moe on Apr 3, 2013 at 4:26pm Add comment
Laser shutter opens [popped open by the "nub" on the toner cartridge it looks like], HV contacts [only 2 on this] are clean and spring up, contact points on cartridge are clean. Transfer roller [sits under toner cart. and is 'behind' flat stainless steel plate in the paper path?] springs up when pushed down, foam on roller is nice and soft. A little noisy when you push down, likely plastic squeaking. So I guess that means it's the DC controller. I expect it is easy when you know how; kind of like field stripping a D-series Dell Latitude. You can do it in about 15 minutes if you know how. Unfortunately, I don't have much field experience with HP printers compared to Dell laptops. Mostly none in fact outside of adding memory and network cards, but hey, there's always a first time! More interesting than dis-assembly will be where to find a 'reasonably' priced board. Thanks for the assistance.

One other thing to ponder; a few months back, the printer was spitting out black pages when printing from an application, but was fine printing test or demo pages. I think that MAY have been a printer cable issue. That seems to have 'healed' on its own and printed fine up until a couple days ago. Last thing printed was about a 20-page, manually duplexed document about 2 weeks ago. The next doc printed on 3/24 was blank, and everything else since has been blank. I think there was a jam on the 20-page document part way through printing the second side, but it finished up just fine. Is there any chance a tiny piece of paper could be stuck in "the wrong place" that would cause the blank page issue?
by Waully on Apr 3, 2013 at 6:46pm Add comment
Not too difficult once you figure out what screws need to be removed to take out each part [and find the 'hidden' ones]. Only 2 parts went flying, but the plastic part is back in place, and one screw is still AWOL. But I've figured out which one it is...

As you've mentioned before, the fuses appear to be fine. Least expensive board I've found so far is a refurbed one for $32 and $11 shipping. Found a "new" one for $62 shipped. I may just be patient and wait for a parts printer unless the DC controller is the part that usually dies first.

Thanks again for the assistance.
by Waully on Apr 3, 2013 at 8:47pm Add comment