🚀 go-pugleaf

    I have a LaserJet+(call it LJ No.1) needed a new fusing roller, so I
 bought one from HP and replaced it myself. However it does not work. I
 than took the whole thing(everything on fig.A) off, put it on another
 LaserJet+(call it LJ No.2), it worked. Place it back to LJ No.1, still
 wouldn't work. After a while I remembered that when error #50 first time
 come up on LJ No.1 was because the connection of fusing bulb was open
 (but after I connect it, the error #50 keeped coming up anyway). I did
 waite 7 min before every power up, and did reset the AC Circuit Break
 on the AC power supply.

    To find out why, I repoduced(not intentionally) the same error #50
 on LJ No.2, and the reason is the same: disconnect the AC power supply
 to fusing bulb. Here is how I did it:

============================================================================
LaserJet+ No.2, works fine

    AC                 thermo-protector                        AC  (Note:
     |                 [O]             [OO] thermistor          |  thermo-
     |  .----------------------------------------------------.  |  protector
     |  :     ___________________________________________    :  |  wired in
     |-------|___________________________________________|------|  seires w/
        :        fusing bulb                                 :     fusing
        `----------------------------------------------------'     bulb)
                 fusing roller
                                                                     fig.A
=============================================================================
Power off, disconnect one side of the fusing bulb

    AC                 thermo-protector                         AC
     |                 [O]             [OO] thermistor           |
     |  .-----------------------------------------------------.  |
     |  :      ___________________________________________    :  |
     |----\ \-|___________________________________________|------|
        :        fusing bulb                                  :
        `-----------------------------------------------------'
                 fusing roller

Turn power on, error #50.
                                                                     fig.B
============================================================================
   Power off, reconnect it (as fig.A), wait more than 7min, power on. It
 passed self test, and waited for 90sec, error message #50.

   Now I have both printers dead and need anyone's help badly.

   Thanks for any help in advance.

Jialin