Hello all,
I am a new member but I have been reading on here quite a lot. My current challenge is that I have an mc2100wa board and I burnt out the r1 resistor that sits next to the external ground wire on the board. I am unable to tell what the value of the resistor is. I am hoping that someone out there has the same board and could help me identify the part.

 

What is the exact No. of the board?, there are several versions.
Max.

 

R1 is a 10Ω resistor referencing the L.V. to earth GND.
It is also in one of the many reverse engineered schematics in this forum.
Max.

 

Thank you, I have looked at the schematics on other posts but my board doesn't seem that common. It is a mc2100WAM Rev-37376. It has the transformer mounted off of the board. I am still learning about circuits and really appreciate the help. I just don't want to replace it with the wrong thing.Thank you again.

 

That was one of the older versions, after that, the transformer was mounted on board.
It is strange that the resistor should burn, as that is just a component to reference the earth GND to the L.V. DC common.
With the resistor lifted, measure the resistance from the L.V. +ve and aluminum heat sink (frame).
Max.

 

I was trying to build a pwm circuit from terry's instructions and for some reason ended up burning that resistor. I must have done something wrong on the breadboard although I am not sure what that was.

 

Your circuit may have been somehow referenced to the AC supply?
BTW the series resistor for the opto LED has to be added as the on board one is too low avalue.
Max.

 

I am unsure what you mean by L.V and +ve. What should the resistance be? Also, are you referring to the r2 resistor next to the upper control board connector?

 

LV +ve is the low voltage DC usually around 11v to 14vdc.
R2 is only 22Ω. so you have to have a suitable resistor in series as this is too low for the Opto LED, depends on what your PWM simulator voltage is.
Max.

 

LV +ve is the low voltage DC usually around 11v to 14vdc.
R2 is only 22Ω. so you have to have a suitable resistor in series as this is too low for the Opto LED, depends on what your PWM simulator voltage is.
Max.

Hi again, I haven't worked on this for a while. I am using an arduino nano with a sketch using 50ms frequency (I have looked at the sketch on an oscilloscope and it is working). I am currently powering the arduino using the usb port on the nano board.

What value of additional resistor would I need for the opto LED?

When I power up the board I only get a solid light, so no signal. I am wondering if I burned out the opto LED. I tried measuring the resistance across the LED in circuit but got nothing.

 

The existing resistor is only 22Ω and the current is 50Ma max.
So you can calculate the resistance required for the power you are using in order to be below 50Ma for the opto diode..
I am using 240Ω from a 5v picmicro
The status indicator LED is fed from the micro.

 

The existing resistor is only 22Ω and the current is 50Ma max.
So you can calculate the resistance required for the power you are using in order to be below 50Ma for the opto diode..
I am using 240Ω from a 5v picmicro
The status indicator LED is fed from the micro.

thanks, I will calculate the needed resistor.
do you think I might have burnt the opto LED? if so can I test it in circuit or do I need to remove it?
is there anything else that would make the board not receive the signal from the arduino?

 

The correct PWM signal and the health of the Opto is about the only thing in the signal input chain.

 

The correct PWM signal and the health of the Opto is about the only thing in the signal input chain.

I tested the optocoupler out of the circuit and it works. is it possible that the 50ms/20hz pwm is the wrong frequency?

 

That is the freq. I am using.
It is possible there are other issues.

 

That is the freq. I am using.
It is possible there are other issues.

I am pretty sure that the arduino sketch is okay. On the scope I can see the duty cycle change and I added a 270 ohm resistor to the output of the arduino (5v). I did find one loose connection and soldered it but it does not seem to explain why I am getting a solid on led on startup. I believe that this means that the board is not getting pwm signal.

I am unsure what else to look at. As you said, the pwm signal just goes directly into the microcontroller. I have checked the resistors and the seem to be working.

 

Is the HV DC present?
Also check pin 10 & 20 on the micro, as well as ensuring the 12v -15v is on HD2 pin 1&2

 

Is the HV DC present?
Also check pin 10 & 20 on the micro, as well as ensuring the 12v -15v is on HD2 pin 1&2

There is 13v on pin 2 on HD2, pin 1 no voltage, both pin 10 and 20 on the micro have no voltage. Also no voltage at the VIN pin on RG1.

 

OK so the micro gets 5v from the 78L05 RG1.
This is supplied from a 12v or 15v zener D8. Which in turn is fed from the Bridge rectifier.
Test the 7W 3.3 K ceramic resistor R9, if yours board is the version that uses R9.

 

OK so the micro gets 5v from the 78L05 RG1.
This is supplied from a 12v or 15v zener D8. Which in turn is fed from the Bridge rectifier.
Test the 7W 3.3 K ceramic resistor R9, if yours board is the version that uses R9.

my board does use R9 and when tested across the terminals I get 3.3k. When I looked at the D8 zener with a magnifying glass it looks burnt. It also doesn't test right with a dmm. I have a limited number of replacement diodes on hand and am not certain how specific the replacement needs to be. Does it need the exact same part for replacement?