asked Oct 3, 2002 at 2:51pm
Hp HP LaserJet 4

HP LJ 4+ display

Have an LJ 4+ with an error 50. Machine sat unused for a time. Replaced fuser ass'y tonight. Powered up, everything looks good, no more error. Print test page, page comes half way out, display and button lights flash and go dark, can hear high pitched tone inside (not fan). Fan still runs but display stays dark.

How do I figure out what blew? There was no smoke, test page looks pretty good, light streaking at top. Toner on test page is fused, no smears.

Damn the luck!

Thanks for any info.

It would seem the power supply fried. The power supply provides AC for the fuser and DC for the rest of the printer. For whatever reason, the fuser must have overloaded it. Never seen that happen before. I feel your pain. They're not that expensive, about $50.
by moe on Oct 3, 2002 at 7:17pm Add comment
Are there any fuses or CB's that could have blown? Is there any chance something else blew also? The cooling fan still runs. I assume that means the DC side of the power supply is OK. Is there any way to check the AC side of the power supply output? I have a multimeter but not knowing which pins to check for current or what the values should be makes it tough.

I tried the engine test button but there is no response.

I hate to keep pouring money into a printer that I can replace for a couple hundred bucks.

Thanks for your thoughts on the power supply.


by unknown on Oct 4, 2002 at 6:11am Add comment
Check the cabling to the control panel.
by unknown on Oct 4, 2002 at 4:19pm Add comment
Was able to swap suspect power supply into another machine. Same dead display. I guess that confirms that the power supply is shot.

Next question is, could there be a fault in the machine that will blow the replacement power supply? I am afraid to swap in a good power supply for fear of ruining it too!

Thanks for any info.


Bruce G.
by unknown on Oct 4, 2002 at 5:04pm Add comment
I've replaced a lot of them and no further problems.
by moe on Oct 4, 2002 at 8:21pm Add comment
Power Supply dead open it up and check all the wiring.
by Stuart on Oct 27, 2002 at 11:48pm Add comment
When it comes to spending money needlessly I am a danger mouse. I opened the power supply and found nothing obviously smoked. Found one place on a cb where two traces run close together that looks odd. It looks like the coating was scraped off across both tracesbut there are no signs of arcing. Probably something stupid and fixable but without circuit diagrams and tools I do not have the know how to figure it out.
by Anonymous on Oct 28, 2002 at 4:07am Add comment
I have a HP 4 and after replacing the power pack and the fuser light, the lights on the display go on but the display is blank. the fuse looks good on the display board but there is nothing, just a blank display.
any ideas?
thank you
by cantfixit on Jun 28, 2008 at 12:25pm Add comment
Check and make sure the connector to the display panel is firmly in place. Does the printer make any kind of start up sounds?
by moe on Jun 28, 2008 at 2:27pm Add comment