| Author |
Laser Printer and DB-25 Switch Box
|
|
|
| I've this on practice test but they don't explain why it is bad to hook a Laser pinter into a DB-25 switch Box. | |
|
| I can't think of a reason off hand why not write the exam folks and see what they say..
oz | |
| Supertech 2004-11-25, 2:12 am |
| Some printer switch boxes cannot process the high data throughput of the printer. Problems can also arise with mechanical switch boxes as damping is increased by the transmission resistance of the switch box.
Hewlett-Packard, which makes the most popular laser printers, warns you that traditional switch boxes can generate surges that damage laser printers. When switching, you can avoid damage by turning the laser printer off - or turning it off-line. Better yet, instead of using a traditional (mechanical)switch box, use an electronic switch box, which has no mechanical switches and doesn't generate any surges. | |
|
| dunno how a mechanical box can cause a surge when it generate no power of its own .
I think what you mean is when old (and very old at that) switch boxes got switched it would get a voltage drop rather than surge . Which could recycle the printer. But that would not damage anything , be no worse than turning of a pc..whilst plugged into a printer powered on..
I have used mech printer switchboxes for years with out a problem. 10 or so years ago switchboxes were most popular method to share printers as it was cheaper than tban a print server and a printer eth card..
May be right for A+ but not in the real world..
maybe the real reason was so HP could sell more jet directs LOL
oz | |
| Supertech 2004-11-25, 3:43 am |
| yeah, that's probably it.
or maybe...
DC is a continuous, uninterrupted flow of electrons which tends to maintain an arc across an air gap.
The problem of switching DC is exaggerated when the load has a significant amount of inductance, as there will be very high voltages generated across the switch's contacts when the circuit is opened (the inductor doing its best to maintain circuit current at the same magnitude as when the switch was closed). | |
| TheShadow 2004-11-25, 3:57 am |
| quote:
Originally posted by 0zzie
dunno how a mechanical box can cause a surge when it generate no power of its own .
oz
Basic EMP (Electro Magnetic Pulse) problems. The opening of any switch is the initial point of magnetic field collapse. The collapsing magnetic field generates a arc if the switch contacts have mechanical bounce. The arcs cause unknown signal status on the cable and can do weird things to the logic board causing failure. A high quality switch will have a serge suppressor circuit to damp the induced surge.
Both HP and NEC exclude warrantee repair if the damage is indicative of mechanical switch box use. The mode of failure is quite specific.
The standard clause in "ALL" models of HP printers .....
"If you are using a mechanical switchbox, ensure that it is equipped with a
surge protector. Damage to your printer could occur from the use of
unprotected mechanical switchboxes.
[...]
The warranty on your HP LaserJet printer shall not apply to defects or damage resulting from:
Operating the printer from a mechanical switchbox without a designated
surge protector."
NEC has similar verbage and both companies have done so long before jet directs or similar networking add ons were introduced into their product lines. It is in the laserjet I and II service manuals. | |
|
| Ok I am not an electrical engineer but unplugging the cable would do the same ???
Its still breaking current ..and it would arc the same as the contacts leave the pins.. ???
But for A+ the answer would be don't use switch boxes..
This is like the NT questions for performance is always add more RAM.
We all know the best answer is to add more Linux... | |
| TheShadow 2004-11-27, 3:31 am |
| quote:
Originally posted by 0zzie
Ok I am not an electrical engineer but unplugging the cable would do the same ???
Its still breaking current ..and it would arc the same as the contacts leave the pins.. ???
But for A+ the answer would be don't use switch boxes..
The A+ answer has always been no mechanical switch boxes simply because HP, NEC and Epson are powerful CompTIA members and they say so. Remember that these are tests of the membership at large and not a single company like Microsoft or Cisco.
Theoretically the same should be true of a cable or people pulling power cords from the mains with equipment on. With a switch box it is worse because the bounce forms a loop between "two" systems and your printer. Each of those systems could be at different levels on each of the pins, especially if one system is trying to print when the switch is thrown. When printers used serial ports with 12 volts instead of 5 volts more people had direct experience with the effects.
No cable is supposed to be removed or replaced with power on but you normally only see motherboard keyboard or mouse ports commonly get munged. The mouse and keyboard ports are fused. The fuses look like resistors or mylar capacitors. In that case I have fixed several motherboards listed bad by inexperienced techs who just replaced the motherboard. It is considered a best practice but they were resurrected into other systems later. |
|
|
|