HP Color LaserJet  3500, 3550, 3700 50.1 Fuser Error
On any HP machine like the HP color laserjet  3500, 3550, and 3700 printers the 50.1 fuser  error is one of the most commonly seen fuser  errors displayed on the machine. The three most common reasons for the error are the power source, the age of the fuser, and the fuser itself. HP Q3655A Color Laserjet 3500/3700 110V Fuser Kit
Troubleshooting the 50.1 fuser error in the HP Color Laserjet 3500, 3550, and 3700 Printer
The first is the power source. because of modern technology more and more devices are getting plugged in around the work area. The result is power strips. Due to the power consumption of these machines it is strongly recommended that they be plugged straight into a wall outlet. Plugging them in to a power strip or battery backup can draw power away from the printer and not allow them to heat up properly resulting in 50.1 or 50.2 errors.
Second is the age of the fuser. As the fuser  ages they get minor scratches in the heating element causing it to take longer to warm up. If it gets to worn then it takes to long to get up to temperature and the printer produces the 50.1 error. In this scenario sometimes just turning the machine off and back on will allow it to get to its correct operating temp because it already is partly warmed up to begin with.
Third is the fuser  itself. Heck, like anything else it will go bad over a period of time. If you get the 50.1 fuser error it is always recommended that you turn the machine off then back on like I mentioned before. Or turn it off, unplug it, and let it sit 10 to 20 minutes then plug back in. If that fails to fix your issue reseat the unit then replace.
HP Q3655A Color Laserjet 3500/3700 110V Fuser Kit
1. Open the lower rear door.
2. Press in on the left hinge (1) pushing towards the right to release the pin, then pull the left side of the tray out and to the left (2) to remove it.
3. Hold the release tabs on each side of the fuser by placing your thumbs on the top tabs (1) and your forefingers on the lower tabs (2). Press up on the bottom tabs (2) to release the assembly and pull it toward you to remove it.
50.1 error – Fuser failure (Abnormally Low Temperature Main Thermistor)
Perform the following steps:
1. The connector between the fuser  and the printer is not connected properly. Reseat  the fuser. Check the connector J5013  between the fuser and the printer. Replace it if damaged.
2. Break in the main thermistor. Turn the printer off and remove the fuser. Measure the resistance between the fuser  connectors J5013LA-2  (MAINTH) and J5013LA-1  (GND). If it is not within the range of 330k ohms to 50k ohms (at ambient temperature), replace the fuser.HP Q3655A Color Laserjet 3500/3700 110V Fuser Kit
3. Faulty DC controller PCB. Replace the DC controller PCB.
Conclusion about the 50.1 fuser error in the HP Color Laserjet 3500, 3550, 3700 Printers
Alright I believe I covered just about everything to check with the 50.1 fuser error in the HP color laserjet 3500, 3550, and 3700. Hopefully you will not have to deal with this error on your machine but if you do it should be easy to fix with the information provided above and the instructions on how to replace it. If you do require replacement of the fusing unit then the link below should get you the part you need.
HP Q3655A Color Laserjet 3500/3700 110V Fuser Kit
Find well displayed printer parts diagrams at: http://www.printerworks.com/
