asked Nov 2, 2009 at 9:30pm
Hp HP LaserJet 4

HP Workhorse LaserJet 4 malfunction. Can you help?

Hi all,
Thanks for a great website filled with useful tidbits. Sadly, my HP4 has been inoperative for the past few weeks, and while this has been the only problem I've ever had with it in 17 years, I fear there may be more on the horizon if I can't repair this.
Here's the scoop;

As for symptoms, the printer began showing ONLY "05 Self Test" on the control panel window and all lights on the panel are lit, with no response from any of the other buttons when pressed. Additionally, as soon as this problem began, I noticed a very distinct but not too loud buzzing sound coming from below the formatter cage area. When disassembled and then powered up with no formatter attached, the buzzing stopped, however, when either the original formatter (or a new one I just received in the mail today) was connected, the noise returned. With the printer apart, I was still able to connect the ribbon cable to the control panel (with either formatter board) and the same message appeared. Interestingly, I've tested the voltages going into the controller board and they are all correct. I am now thinking that it must be the power supply unit, though how is that possible since the voltages are fine (and fan operates fine)? I've also replaced the controller board, and the effects are the same; no change.
Thank you in advance!
Will it do an engine test with the formatter removed?
by moe on Nov 3, 2009 at 9:50am Add comment
Hi Moe,
Thanks for the thought...I haven't tried that (and have to consult the service manual first to see how it is done).
I'll check back.

by Pascuzzi on Nov 3, 2009 at 3:47pm Add comment
????? Why do you need to consult the manual when I gave you a link with a picture???? - moe
Thanks for the kind words Moe, and yes, I did check the image, but also wanted to read about it more clearly in the service manual just to verify. Either way, with the printer disassembled, the feature does not work. I'm awaiting a new power supply tomorrow.

Thank you for your help.
by Pascuzzi on Nov 3, 2009 at 7:17pm Add comment
FYI, the HP4 is back in working order. Apparently, the electrolytic material in a capacitor on the power supply board dried up (to be expected after nearly two decades) and the PS was replacede with a new (old stock) one. The printer is back in working order and is great, and page count is 88770.

by Pascuzzi on Nov 5, 2009 at 9:54am Add comment