Bad solder effects - The first step in every home repair...

[krytron]

This applies to all models and types of CE.

What I'm not sure about is the type of problems bad solder can cause.
I can imagine it increases resistance and lowers the current thus causing the current to be below its normal value.
On the other hand, it increases the voltage drop so if some regulator takes reference value from it, the output would increase above normal value.
All in all, bad solder would either cause lower-to-normal or above-to-normal values for a particular signal, but never both.

Right, wrong, or undecidable?


Thanks.

[krytron]

I thought it's one of the most rudimentary things to know when doing repairs.

[krytron]

Nobody, even a word or two

[vtech]

Bad solder joint (same as cold solder) is the same as a broken/intermittent connection between two points. If there is high current involved, it will cause it to heat up and creates a voltage drop.
Depending on the severity of the junction, it will begin to attenuate and act like a resistance in the path of a signal.

[krytron]

If you read my first post, that's exactly what I wrote about bad/cold solder (except for excess heating).
Cold solder causes intermittent changes in voltage or current. It increases resistance, so it generates additional voltage drop - everything clear so far.

When bad/cold colder "kicks in", generally one of the following happens:

1. some electrical value drops below its nominal value
   
2. some electrical value jumps above its nominal value
   

In my monitor problem, "some electrical value" is the red signal voltage, which both drops below and jumps above nominal value. So the question is can bad solder produce the third type of the problem:

-> 3. some electrical value randomly and intermittently drops below and jumps above the nominal value

[krytron]

Can't edit own posts, so have to make another...

Spell error in the above post: colder = solder, of course.

Wanted to add that above-and-below nominal value jumps of the red signal level make me crazy, as I can't distinguish between bad solder and potentially bad IC... plz help.

[vtech]

Perhaps instead of keep repeating yourself, if you spend a little time to read about basic ohms law or how an RGB circuit suppose to work, you may have a better understanding.

ONE MORE TIME;
For a signal to get from point A to B, it must have a solid connection in order for the electrons to flow. If and when there is a break (ie cold solder) between A and B, there will be a break in signal path, meaning that it can ONLY cause a decrease in value no matter what type of signal is passing through.

Rather than pondering about a cold solder joint's behavior, If you have a fluctuating red signal, the correct way is to look at the print and follow the signal from the source to destination. You may have to use a meter or a scope to spot check the signal along it's path. There may be bad connection anywhere in the signal path or even a problem in the drive circuit that generates the control signal. Depending on the unit, it may be difficult or awkward to access certain points but that is how is done.

[vtech]

[vtech]