Hotend slow heating

The hotend heats too slow. It takes appropx 20 min to reach 200 deg.
When I press the heater on button, the heater LED on the Ramps illuminate. I measured the voltage between the D10 POSITIVE terminal and supply GROUND (NEGATIVE) from my power supply (PS). I get 12v even when the hotend is not being called for as long as the PS is on. I also measured the voltage between the pin on the MOSFET furthest away from D10 and the supply ground. I got 12v when the hotend is being called for. But when I measured the D10 output voltage I got close to 5v (when the heater is on, I think here I ought to have 12v?).
At first, when I have just assebmled my printer, everything was okay. But then gradually this problem with slow heating came up. It was harder and harder for heater to reach and sustain required temperature. And now it can't reach it at all. Unfortunatelly I can't connect this problem to any particular event.
I don't think that the problem is in the software (Marlin). Because I haven't made any essential changes there.

I have RAMPS 1.4 and this Makergear's hotend – [www.makergear.com].

The +12V side of RAMPS is always on. The side that is switched is the -ve side.

If you measure +12V on one pin to ground when the heater is on, but don't measure 12V across the hot end (from one pin on D10 to the other) while on, you most likely have one of the following issues:
1. D10 connector is faulty.
2. FET for D10 is failing or failed. You may also check it's actually a FET, as some vendors have been known to populate boards with the wrong components because the vendor is cheap and they skimp on QA/Testing.

The same sort of thing applies for D9 and D8.

If you don't measure +12V to ground when the heater is on (significantly less than 12V), then check the PTC fuses (the 5A one is used for D10/D9, the 11A one for D8) to make sure they're working, or replace them with real automotive fuses. The PTC fuses reduce the current when too much is being drawn (by increasing their resistance) so they end up dropping voltage. This may mean you're drawing too much current (eg: some sort of short) but it could be that your setup just exceeds the normal expected ratings for the PTC fuses (eg: too warm, slightly too much current, the PTC fuse tolerance is just slightly under what your system expects, etc).

Quote
Cefiar
If you measure +12V on one pin to ground when the heater is on, but don't measure 12V across the hot end (from one pin on D10 to the other) while on

This is the case.
I tried to test FET for D10. I wanted to see if there is voltage at the gate of the FET. As you said in your (Cefiar) post here [forums.reprap.org]. I measured the voltage at R13 and ground (-V of power supply), when the hot end is on. And I got ~2V. But I don't really understand both sides of what you where talking about in that post. Please explain if you can.

I also tried to swap D10 and D9 around. I changed pins.h in Marlin. But the problem remains. The wires of the hot end was connected to D9. I didn't get 12V (only ~5V) from one pin on D9 to the other (when the hot end is on).

Edited 1 time(s). Last edit at 06/17/2014 05:44PM by Memphis.

I would look at:
1. The resistance of your hot end.
2. What the "FETs" are actually labelled as.