V7 Pull-up module resistor burned up

[Stephan Schmitz-Justen]

Hey Guys!

New to the Forum and new to Guzzis! I just got a custom V7 and I am redoing some of the messy wiring the previous owner left behind and I stumbled upon a burnt up pull-up resistor as seen in the image below.





When took it out of the heat shrink I could see that the part is simply a small diode and a larger resistor. The diode is fine and I was able to get a measurement of 220 Ohms from the resistor, but I believe this to be too little and I was not able to find the information on the resistance elsewhere on the web. Due to the resistor being burned, I cannot assume that the resistance is correct and cannot read the part number on the piece to look it up.

I do not wan't to pay the 50ish dollars for a new piece (Part number 887948) if I can replace just the resistor for maybe a dollar or two. I was wondering if anyone would be willing to look at their part and see if you can read the information on the resistor or measure it. If you cannot read it and have to measure it you would need to take off the heat shrink.

I think it would be great to have the information for the pull-up module on the forum so no one has to shell out 20x what it costs to make the part.

 

[Kevin.NZ]

What caused the resistor to overheat, what does it actually do in the circuit?

 

[kiwi dave]

Kevin, it appears to be part of the clutch switch operation, and is simply a resistor and a diode in series. How they can justify €49.90 for a simple diode is beyond belief. This price doesn't include the series resistor either.

I'm guessing there might have been a short around the clutch switch or the side stand switch that caused excessive current to cook the resistor.

I can't identify what the device is between the resistor and diode, perhaps it's just a crude jointing mechanism.

I'd be heading to Radio Shack for replacements. 220Ω for the resistor seems credible to me.

 

[Kevin.NZ]

Looks like its a crude tubular crimp joint. As you say 220 ohms seems correct as resistors go "open or high" when abused.

 

[Brian UK]

The wattage rating of the resistor is just as important, preferably get one to a higher rating.
What does pin 14 on the ECU connect to?

 

[sib]

From your second pic, the resistor doesn't look to me like it's "burned up". Perhaps it's good and it's supposed to be 220 ohms. I can see the melt hole or possibly abrasion hole in the overwrap plastic tubing, but that doesn't mean the resistor has actually overheated. BTW, at 12.5V, 220 ohms would dissipate 0.71W, enough to create some warmth. A 2W resistor would be appropriate.

 

[GTM®]

New to the Forum and new to Guzzis! I just got a custom V7 and I am redoing some of the messy wiring the previous owner left behind and I stumbled upon a burnt up pull-up resistor as seen in the image below.

Hi Stephan, welcome to the GT Forum & Guzzi Famiglia. Assume LA County is Los Angeles based on your avatar, yes? If so, we have a solid Guzzi community here in SoCal. Hope you'll also add your info to our Registry; https://www.guzzitech.com/forums/threads/v7-registry-picture-thread-add-your-bike.9108

On that 887948 resistor, were you getting a check engine light or did you just stumble on it?

 

[Stephan Schmitz-Justen]

Hey guys,
thanks for the responses and warm welcome!

Looks like its a crude tubular crimp joint. As you say 220 ohms seems correct as resistors go "open or high" when abused.

It is indeed a crimp joint. At 220 Ohms you get about 50mA, which I believe to be a lot for a simple input switch. You usually see pull-up resistors in the 10k range, but maybe the Italians do it differently?

On that 887948 resistor, were you getting a check engine light or did you just stumble on it?

I just stumbled upon it. My bike sadly does not have the stock dash and has no check engine light. Once I have more of the wiring back together I will check if it is on.

From your second pic, the resistor doesn't look to me like it's "burned up". Perhaps it's good and it's supposed to be 220 ohms. I can see the melt hole or possibly abrasion hole in the overwrap plastic tubing, but that doesn't mean the resistor has actually overheated. BTW, at 12.5V, 220 ohms would dissipate 0.71W, enough to create some warmth. A 2W resistor would be appropriate.

Yeah definitely need to go with a 1-2W resistor. But I will also see what kind of resistance I get when measuring pin 14 and 19 to ground and I'll report back here. The resistor definitely had heat damage to it and it looks like it came from the resistor itself.

Thanks again for all the help guys!

 

[Stephan Schmitz-Justen]

Made a little image to show what the circuit fully looks like.

Found this info online
"The value of the pull-up resistor needs to be chosen to satisfy two conditions:

1. When the button is pressed, the input pin is pulled low. The value of resistor R1 controls how much current you want to flow from VCC, through the button, and then to ground.
   
   
2. When the button is not pressed, the input pin is pulled high. The value of the pull-up resistor controls the voltage on the input pin.
   

For condition 1, you don't want the resistor's value too low. The lower the resistance, the more power will be used when the button is hit. You generally want a large resistor value (10kΩ), but you don’t want it too large as to conflict with condition 2.
The general rule for condition 2 is to use a pull-up resistor (R1) that is an order of magnitude (1/10th) less than the input impedance (R2) of the input pin. An input pin on a microcontroller has an impedance that can vary from 100k-1MΩ."

R2 would be the resistors in the ECU which should be easy to measure and then it'll be quick math and we have needed resistance.

 

[kiwi dave]

What button are you pressing?

 

[Stephan Schmitz-Justen]

What button are you pressing?

Sorry it wasn't clear, that excerpt was pulled off this page explaining pull up resistors in general. https://learn.sparkfun.com/tutorials/pull-up-resistors/all

So the button would be the clutch switch.