Printer problem solved, but why did it work?

J

JOhnH

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After a momentary power flicker, my HP Officejet Pro gave a paper jam error. I thoroughly looked for any stuck paper and found none. I turned the thing off and on, but still got the same error. I pulled the plug from the back and put it back in and got the same error. I left the plug out over night and the next day I got the same error.

So I googled the problem and one of the myriad solutions said to:

Make sure the printer is turned on.
Then unplug the cord from the back of the printer,
THEN unplug the cord from the wall. (It is just a plain, dumb power cord as far as I can tell).
Wait 15 seconds,
Plug the cord back into the wall.
Plug the other end of the cord back into the printer.

It worked, but why? What did unplugging the cord from the wall do that unplugging it from the printer itself didn't? I have seen this work before, but I never understood why.
 
When you say it's a plain, dumb power cord do you mean it's just a straight 120v AC going straight in or is there a box somewhere between the wall and printer that's converting the outlet power to DC? Some of those boxes are so efficient they'll keep providing power for a brief period after being unplugged so maybe in theory it didn't completely power off the printer and reset whatever error had tripped.

Another note, instead of a power off/on is there a cover/panel somewhere you can open and close? Most printers I've seen will set a "paper jam error" and not allow anything further to happen unless you open/close a certain panel. Unplugging it probably resets the error as well but there might be an easier way to do that.
 
JOhnH said:
After a momentary power flicker, my HP Officejet Pro gave a paper jam error. I thoroughly looked for any stuck paper and found none. I turned the thing off and on, but still got the same error. I pulled the plug from the back and put it back in and got the same error. I left the plug out over night and the next day I got the same error.

So I googled the problem and one of the myriad solutions said to:

Make sure the printer is turned on.
Then unplug the cord from the back of the printer,
THEN unplug the cord from the wall. (It is just a plain, dumb power cord as far as I can tell).
Wait 15 seconds,
Plug the cord back into the wall.
Plug the other end of the cord back into the printer.

It worked, but why? What did unplugging the cord from the wall do that unplugging it from the printer itself didn't? I have seen this work before, but I never understood why.
Click to expand...
Maybe not the same phenomenon, but I have observed that devices that contain a microprocessor (what doesn't anymore?) can get "locked up", and be unresponsive for as
long as power is applied. A quick power-up reset won't fix it, but a long period with everything disconnected often will. I have seen that several times with 2-way Radio
Repeaters (on mountaintops, of course). Onsite they are powered up but totally unresponsive. Pull them out and take them back to the shop - and Voila! the problem has
vanished. Kind of makes you doubt your sanity.

My own HP Photosmart C6180 has what I take to be a bad internal electrical contact. Sometimes while printing it will stop what it is doing and start to make growling
noises, accompanied by the display blinking on and off. I have learned through trial and error that the cure is to hit it with my fist on the left front top corner (Seriously -
fixes it every time!). It's about ten years old, and I have been waiting for it to die (so I can upgrade) - but it just won't quit. I don't do enough printing to get upset abiut
it.

Dave
 
SkyDog58 said:
Removing all power and turning it back on has also been known to fix a CRJ.
Click to expand...
But wouldn't just removing the power plug from the back of the printer remove all power? Especially since I left the power plug out all night. Why does the cord need to be removed from the back of the printer, AND from the wall?
 
JOhnH said:
But wouldn't just removing the power plug from the back of the printer remove all power? Especially since I left the power plug out all night. Why does the cord need to be removed from the back of the printer, AND from the wall?
Click to expand...

Beats me. Removing the power adapter plug from a device has fixed things for me before that simply turning off power did not but I’ve never had to unplug both ends of the power adapter/cord before.
 
This is blowing my mind. I'm not an electrical engineer but if it truly is a dumb cord, I cannot see how this can be. I would say it was a pure coincidence and what really fixed it was just the multiple disconnects but if it is true you have seen it before, then the chance of coincidence is reduced.

Are they just having you make sure the plug is tightly seated in the outlet? Although AFAIK it either is or isn't getting power to the printer and if it powers up before but just doesn't clear the error, I don't know how the plug being not seated tightly enough would matter, if it were enough to be conducting power.

Only other thing is maybe some cords look dumb but actually have some sort of tiny capacitor or some chip in there that isn't obvious. I wouldn't think that would be the case but they are starting to put "smart" brains into all sorts of stuff these days. Still wouldn't think a cord would have that.
 
Rushie said:
Only other thing is maybe some cords look dumb but actually have some sort of tiny capacitor or some chip in there that isn't obvious. I wouldn't think that would be the case but they are starting to put "smart" brains into all sorts of stuff these days. Still wouldn't think a cord would have that.
Click to expand...
That's about the only explanation I have been able to come up with too.
 
JOhnH said:
That's about the only explanation I have been able to come up with too.
Click to expand...

Then it is obvious what you must do. Perform a dissection on the cord and provide us with a pathology report.:D
 
JOhnH said:
But wouldn't just removing the power plug from the back of the printer remove all power? Especially since I left the power plug out all night. Why does the cord need to be removed from the back of the printer, AND from the wall?
Click to expand...

To give you something to do while the caps drain would be my guess.

When I was doing tech support, there were times when I needed the client to reboot the computer and just leave it alone for a while because I had things happening during boot (usually related to malware removal). I would tell them to reboot the computer and run over to the modem and router, and keep me updated on which lights were blinking. Worked pretty well.

Rich
 
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