Heatbed wont turn on after converting Wanhao duplicator I3 from Melzi to RAMPS

Hi all. I tried this same question over in the Repetier forums... I thought it was a software thing, but they think it's hardware. Hoping someone here can shed light on my ignorance!

Background: I bought a Monoprice Maker Select v2 (aka Wanhao DI3). With only minor tweaking, it printed PLA great out of the box. I started my first ABS print after a month of PLA prints, and it was struggling to reach temp... took the bed a long time to climb to ABS temps... and then there was smoke from the control box. I unplugged everything, let it cool, and found that the heatbed connectors to the Melzi had melted. Rather than RMAing the whole thing (which would have been a lot quicker, but much less 'fun'), or just replacing the connectors, I started looking at DIY options. Ultimately ending up with RAMPS 1.4. I've done a full replacement of the Melzi. I'm running repetier firmware and host. I even picked up an separate heatbed mosfet (Trigorilla).

From the host, all the controls (x,y,z,extruder and hotend) and sensors (stops and thermistors) work as expected, except for the heatbed. When I turn on the heatbed, the RAMPS led lights up, the power supply buzzes, and the temp on the heatbed doesn't climb. I have 12V power running into both the 5A and 11A terminals. But, there's only 5V coming out of D8 when the heatbed is turned on in Repetier... shouldn't this be 12V?

I was suspect of my RAMPS board. I tried with a new RAMPS and the results were the same. For good measure I even tried a new Mega, with the same result. ...I even switched out a a new power supply, bupkis.

For what it was worth, when I had the heatbed connected directly to the RAMPS (before I had the off-board heatbed mosfet connected), the mosfets on the RAMPS would get blazing hot. I did google some articles that suggested that my mosfet wasn't getting proper trigger voltage. It kinda still feels like the same problem, since there's only 5V coming off the D8. I just don't know how to confirm or fix it if it is the problem.

The bed hasn't worked right since I replaced the Melzi with the RAMPS... so I could have wired something wrong. I have the polarity right on the power connections, but could any other connections' affect the mosfets? .

What should I check next?

do you still get 12v at the power supply when the heatbed in on ?
What resistance does the heatbed measure (when disconnected from the ramps)

Hey Obewan,
I get 1.1 ohms on the heatbed. I have 12.03v coming off the power supply, and that doesn't change at all when I turn the bed on.

Here's a picture of my mess, maybe it'll help. Just off the to right I have my reprapdiscount full graphic smart controller...

Your wiring looks ok so only other thing i can think of atm is the 5v rail, is it holding 5v ok or is it low? (measure on a endstop connector)

I checked x and y endstops, they're both reading 4.99v.

I started probing around, and I don't know if these mean anything (I should have mentioned that most of my electronics' experience has been had dealing with this issue),

For what it's worth also, all my mosfets are IRF-3205s.

With the hotend off, the hotend mosfet (Q1) pin 2 reads 12.02v. other pins are 0v.
With the heatbed off, the heatbed mosfet (Q3) pin 2 reads 11.26v. other pins are 0v.

With the hotend on, the hotend mosfet (Q1) pin 1 reads 5.04v, pin 2 reads 0.12v, pin 3 reads 0.04v. To me, it looks like it's spot on.
With the heatbed on, the heatbed mosfet (Q3) pin 1 reads 1.96v, pin 2 reads 6.82v, pin 3 reads 0.0v. something in the power supply buzzes too when it's on, but I already mentioned that above.

The 1.96v on Q3 pin 1 (gate) indicates that the fet is not being turned on fully,
In repetier firmware are you using 'bang bang' or PID for the bed control ?

In repetier host, temperature curve tab, does it show the bed being turned on full or pulsing.

Obewan, nearly got it...

I'm using PID control (my configuration.h has #define HEATED_BED_HEAT_MANAGER 3).

I checked the temp curve (I didn't know it was there, thanks for introducing me!)... and it said my output was 39%. I suppose it's no coincidence that 39% of 5.04v is 1.96v, the exact numbers I got above. I noticed my HEATED_BED_PID_MAX and HEATED_BED_PID_INTEGRAL_DRIVE_MAX were both 100... which I thought was a percentage, but that's on a scale of 0 to 255... again no coincidence that 39% of 255 is 100. So... I recompiled my firmware with those set to 255.

I restarted repetier host and nothing was changed. I soon found that eeprom settings were overwring my configuration.h settings... I'm not sure where those are coming from, but I'll find em (suggestions?). I sent an M502 command and I'm finally getting heat! But, as you mentioned, it's pulsing (even when it's full-on, I hear a ticking (almost sounds like arcing) from the power supply. but I'm guessing it's the PID control still at work). turning on for a bit, then as temp climbs, it starts turning on/off quickly, multiple times a second at times. I guessing there's more wrong with my config settings.

So, serious progress. Serious thanks to you. If you have any recommendations on config values, they'd be welcome.


// ############# Heated bed configuration ########################

#define HAVE_HEATED_BED 1
#define HEATED_BED_MAX_TEMP 120
#define SKIP_M190_IF_WITHIN 3
#define HEATED_BED_SENSOR_TYPE 97
#define HEATED_BED_SENSOR_PIN TEMP_1_PIN
#define HEATED_BED_HEATER_PIN HEATER_1_PIN
#define HEATED_BED_SET_INTERVAL 5000
#define HEATED_BED_HEAT_MANAGER 3
#define HEATED_BED_PID_INTEGRAL_DRIVE_MAX 255
#define HEATED_BED_PID_INTEGRAL_DRIVE_MIN 80
#define HEATED_BED_PID_PGAIN_OR_DEAD_TIME 196
#define HEATED_BED_PID_IGAIN 33
#define HEATED_BED_PID_DGAIN 290
#define HEATED_BED_PID_MAX 255
#define HEATED_BED_DECOUPLE_TEST_PERIOD 300000
#define MIN_EXTRUDER_TEMP 150
#define MAXTEMP 275
#define MIN_DEFECT_TEMPERATURE -10
#define MAX_DEFECT_TEMPERATURE 290

PID and my heatbed aren't working so well, but I switched it to bang bang and it's heating well enough. Obewan, thanks again for helping me break through this.

to update eeprom with settings from config send
M502 ;reads config
M500 ;saves to eeprom

glad you got it working