HP Printer USB / Power Cord Issue - Bizarre

Fred Marshall
07-09-2005, 10:30 PM
Customer has an HP 1300 Laserjet and intends to use USB.

Many attempts to make it work failed - apparently affecting the setup of the
DOT port.

Finally noticed that HP recommends plugging the printer's AC power into the
wall and not into a power strip *and* to use the power cord supplied with
the printer. Doing the former (and maybe the latter, I don't know) solved
the problem!


The printer has a very susceptible power supply that can't stand any
filtering between the printer and the source of AC power.

Any others? Comments?



07-09-2005, 10:30 PM
"Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote in message
> The printer has a very susceptible power supply that can't stand any
> filtering between the printer and the source of AC power.

Well it might be that but I suspect it's not quite that exactly....

It's possible that a loop exists and that noise on the mains or another
source is coupling into this loop and preventing or corrupting the data on
the USB cable. I've seen two pieces of equipment that work fine on their own
but which fail/crash when they are connected together. A typical loop might

power lead of computer
case/0V of computer
cable/cable screen
case.0V of printer
power lead of printer

The loop may not be exactly like that - it can involve capacitive coupling
between signals that aren't connected together directly. It can be very
difficult to fix this type of problem as both manufacturers can claim their
kit is ok. Sometimes they are forced into this position by the standard for
the interface cable between them.

Solution: What's usually important is the AREA of the loop so one possible
solution is to try and reduce that - perhaps by moving equipment closer
together, shortening data cables and removing extension leads or otherwise
changing the physical layout to reduce the area. I've had to resort to
twisting the mains leads together and plugging them into adjacent wall
sockets or adjacent sockets on a filtered mains block.

This can sometimes be a bitch to fix. Sometimes doing the opposite of what
the theory tells you works for no obvious reason! You can hire monitoring
equipment that monitors and records mains transients so if the problem comes
and goes you can try and correlate the two.

Some makes and models of equipment are probably more susceptible than others
but I've no idea if this is true of the kit you mention.

Is this in a factory? Got any manufacturing equipment nearby? Radio
transmitters? Air conditioning units?


HP Printer USB / Power Cord Issue - Bizarre