Channel Imbalance in DAC


Posted on Feb 7, 2014

Tested all the resistors and noted 2 resistors` readings were out compared to the other channel (i. e.1. 2Kohm vs 2. 2 kohm). Based on the color codes, should be 2. 2kohm. THought I spotted the problem, repl the `1. 2kohms` with new 2. 2 kohms but the problem persist. The new resistors still reads 1. 2koms and the desoldered ones seems ok reading at 2. 2.


Channel Imbalance in DAC
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i. e. the resistors seem to have almost halved the value when mounted on the board ! Tested all the resistors and noted 2 resistors` readings were out compared to the other channel (i. e. 1. 2Kohm vs 2. 2 kohm). Based on the color codes, should be 2. 2kohm. THought I spotted the problem, repl the "1. 2kohms" with new 2. 2 kohms but the problem persist. The new resistors still reads 1. 2koms and the desoldered ones seems ok reading at 2. 2. i. e. the resistors seem to have almost halved the value when mounted on the board ! If you`d just said that the resistor measured wrong, I`d have thought that you were a novice who didn`t appreciate that a resistor on the board may not read it`s printed value because there are other components in shunt (parallel) with it. The fact that the other channel measures correctly, however, means that there is a definite problem. The problem MUST be in something that is connected to the 2 resistor terminals, either at the pads or somewhere on the tracks that connect to them. That could be a chain of components, or a single component. There should be be an open circuit between the pads for the problem resistor (when it`s removed), but instead there is a resistance of ~2k6 (by calculation). The most likely cause is a solder string somewhere, probably introduced when you replaced the caps, but it could be a tiny piece of loose solder or cut component lead, or a faulty cap. I`ve even seen (detected)...




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