Electronics Question

Ripweade

Active member
Joined
May 6, 2010
Messages
987
Reaction score
58
Location
Pennsylvania
Quick background. My breathalyzer isn't working right. When I turn it on, it can detect alcohol pretty good. But, as it stays on, it doesn't detect a thing. In other words, it seems to slowly stop registering the longer it's plugged in. I just bought a new sensor and plugged that in, but no difference.

I was originally thinking that it could be a leaky cap on the board, but not too sure now. I individually bridged three of the four on the main PCB with good caps and no difference. There is a huge 10000uf cap on there which I don't have, so I didn't test that.

I tested the power supply, and it's outputting 5vdc fine. I didn't check under load, but at difference spots on the main PCB, I was getting a 5vdc reading, so I am assuming the power supply is fine.

Everything else is working except for registering alcohol in the sensor. Last week, I did have to reflow solder to an LED lead because the solder joint came loose.

My question: What could cause a machine to work fine when initially turned on, and then slowly stops registering the longer it's on? Could this be more bad solder joints that are breaking contact somewhere when the machine warms up? I'd think not since heat expands, but I could be wrong.

Any teachings in electronics here is appreciated. :)

Thanks in advance!!!

Bill
 
Usually when a device works initially then slowly stops working the issue is heat related. At least in my experiences...
 
Faulty IC's can work when cold but not when hot. Take a can of compressed air and turn it upside down, and spray suspect chips with it after the device stops working, and see if it comes back to life.

Also, as resistors heat up, they can drift. Are there any largish resistors that are getting hot?

Also, bad solder joints are very common on modern electronics, especially with surface mount parts. That's the primary reason behind the Xbox 360 failures. Having never seen inside one of these devices, I don't know what the board looks like - does it have a lot of surface mount chips?

-Ian
 
There's a few surface mounted chips, but not the most. Two are socketed and the rest are right on the board.

I'll have to check the resistors. There are a few on the board but not any big, ceramic ones or anything like that.

Thanks for the input so far! It's giving me a great place to start instead of taking the shotgun approach. :)

Bill

On a side note, I've had this machine for about 6-7 years but haven't used it much. I've turned it on maybe once or twice a year and it's worked fine. It was until a couple weeks ago when I left it on that I noticed the sensor losing its sensitivity.
 
Last edited:
Back
Top Bottom