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Post by jamirie on Dec 29, 2012 14:01:55 GMT -5
Pic 1 Attachments:
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Post by jamirie on Dec 29, 2012 14:03:44 GMT -5
Pic 2: (hope you can identify what you're looking for...) Attachments:
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Post by airtripper on Dec 29, 2012 16:21:07 GMT -5
Looks like there might be a couple of solder bridges that should not be there, including the you spotted earlier (circled in red). Also, it looks like you have some poor solder connections like those circled in blue. The soldering looks a bit untidy and there should be no solder bridges like those circled in red. Where the blue circle is there are 3 resistors that form part of the voltage divider when the thermistors are connected. When the thermistors are not connected, you should be getting 5 volts across each resister. Remove everything from the ramps board and connect it to the mega board and apply power from usb and carefully measure the voltage across the resistors. Use one of the AUX connector ground (GND pins) to ground the multimeter. Attachments:
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Post by jamirie on Dec 29, 2012 17:40:54 GMT -5
Hi Mark, so i measured just as you described - all outputs around 4,95V.. (great description for a noob like me *thumbs up*) In my picture the briges seem to be cause of the angle but there weren't any bridges. Took a better pic: Attachments:
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Post by airtripper on Dec 29, 2012 18:32:47 GMT -5
Using the same ground point, use the multimeter to measure each thermistor pin connector. One pin on each thermistor connector should measure 5 Volt while the is 0 volts. Then measure the pins on the ramps board that plug into A13, A14 and A15 on the mega board, which should be 5 Volts. You may have to separate the boards to note the pin labels on the mega board. Or you could use the guide image of the mega board below. If the voltages are correct, with the mega board plugged into the usb socket, start Pronterface and check the temperatures. They should read 0 at this point. If you get 0 degrees, power down, connect the thermistor to T0, power up and check the temperature in Ponterface again. We are looking for ambient temperature here. Hopefully you'll report back with a good result. Attachments:
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Post by jamirie on Dec 29, 2012 19:25:23 GMT -5
One pin at T0 seems to have not enough voltage... EDIT: The A13 Pin has the same output like the T0 pin... where to find the issue??? Attachments:
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Post by airtripper on Dec 30, 2012 13:24:34 GMT -5
This is good news because this explains why you get a reading without the thermistor plugged in I think.
Pins A13, A14 and A15 on the mega board samples the voltage coming from the resister/thermistor voltage divider at pins T0, T1 and T2.
The 5v supply is routed through the resistor, then through the T0 connector and then to pin A13. You have already measured 5v at the resistor for T0 so the problem area could be between the resister and the T0 connector. Use the schematic to identify the trace between the resistor and T0 connector.
Measure the voltage on both sides of the resistor For T0. If the voltage on one side of the resistor is as low as that on pin A13 then the resistor may be faulty and need replacing. If the voltage is normal then you need to check that the T0 pins are not shorted together causing the the 5V to short to ground.
But first, measure for 5v on the T0 pin again while pressing a finger or something onto the resistor on the same trace to rule out loose solder connection on the resistor leg. Testing the resistor with the multimeter probe could be making a temporary connection across a badly soldered joint giving a false reading.
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Post by jamirie on Dec 30, 2012 13:54:43 GMT -5
Great suggestion! So one of the resistors seems to be dead! Measured both sides of the corresponding T0 resistor to ground= one side of the resistor shows 4,95V, the other one 0,15V. Seems like the issue could be solved soon Is the resistor i need to replace a 4.7K resistor (250mW 1%)? EDIT: I occasinally have had an 4,7k resistor here, exact the same like the original one- but still the same issue! 0,15V from T0 resistor EDIT #2: I desoldered and measured the one output pin of the T0 resistor to see if it is an issue with the circuit after the T0 resistor- Output is 4,95V when not soldered to board.... And so it seems there's an issue after the resistor causing the output drop.... Next, following the traces, are the capacitors- but how to test em? Any ideas???
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Post by airtripper on Dec 30, 2012 17:50:08 GMT -5
You are looking for the point where the voltage changes from 5v to nothing.
Check the positive side of the capacitor to see if there is 5v there. If that fails, remove the capacitor and measure the pad again. With 5v at the resistor you should be getting 5v at the capacitor and the T0 connector pin.
Desolder the T0 connector, clean the pads and do a measure on the pads. You should be getting 5V between the resistor and the T0 connector pin.
With the power disconnected, you can check the continuity between the connector pin and the resistor. If the continuity fails, there might be a fault on the trace and you might have bridge that gap between the resistor and the connector with a wire. But there should also be 5v supplying the capacitor as well.
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Post by jamirie on Dec 30, 2012 19:17:39 GMT -5
How can i check the capacitors? When RAMPS Board is connected to arduino board to supply power, there's no chance to get onto the pins where i can measure... Think i have to desolder it... but how to measure a capacitor like this?
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Post by airtripper on Dec 30, 2012 20:22:27 GMT -5
It's best just to remove the capacitor and measure the pad. No need to measure the capacitor itself. We just need to confirm that 5v is being at least supplied to the capacitor. Also, by removing the capacitor we can see if that makes a difference to the voltage level on the thermistor pin.
The resistor will need to remain soldered in place while you measure the solder pads for the capacitor and the T1 connector. You can also do a continuity test between solder pads that should be connected through traces when the ramps board is not powered.
We need to find out why the T0 connector is not getting 5v from the resistor when there is 5v across the resistor. The ramps board may have a faulty trace or pad, and we need to confirm that before we can fix it.
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Post by jamirie on Dec 31, 2012 5:17:18 GMT -5
I desoldered the 1st capacitor (for T0) and measured the pads while the resistor is soldered in... still 0,15V Seems like there is a problem with my PCB... It may generates a short somehow... hmmm... too bad...
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Post by airtripper on Dec 31, 2012 14:12:52 GMT -5
Check the image and confirm voltage levels at points marked. Also confirm what the voltage is at the question mark. I take it that you have not been able to do a continuity test on the trace between the capacitor and the resistor; and the T0 and the resistor. I use the test a lot when working on my own circuits. You can connect T0 and the capacitor to the resister with wire to bypass a faulty trace. Just solder the wire to the pads after adding the components. If the resister pad is faulty then adding the wires should restore the rest of the trace to 5v. If there is a short then nothing will change after adding the wires. Attachments:
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Post by jamirie on Jan 1, 2013 14:23:58 GMT -5
Continuity is given on the traces between the capacitor and the resistor... I did not understood how to bypass? You mean solder wires to the capacitor (instead of stick it in the PCB) and directly connect it to the resistor? Thanks for your kind assistance Airtripper Attachments:
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Post by airtripper on Jan 1, 2013 19:19:45 GMT -5
We needed 5v on both sides of the resistor to consider a wire bypass. It now looks like there is a short somewhere along the trace.
Step 1. In case you have not done so already, remove the capacitor and do the test again on the same points circled on the last image posted. We want to rule out the capacitor shorting the circuit to ground. If you still only get 0.15v then go to step 2.
Step 2. Using the last picture you posted, de-solder and remove the resistor leg where the big arrow is pointing. Then measure the voltage on that resistor leg while it is stuck up pointing away from the board while the other leg is still connected. We want to see if that resistor leg changes from 0.15v to 5v when it is not connected to the capacitor trace.
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