Electronics > Repair
Video Teardown and Repair of an Agilent E4421A Signal Generator [TheSignalPath]
Hugoneus:
In this episode Shahriar repairs an Agilent E4421A synthesized signal generator purchased from eBay. The unit displays the error messages “UNLOCK” and “UNLEVEL”. The cause of failure is investigated and traced. Alongside the repair efforts, the internal construction and components of the synthesizer are also presented. A short tutorial on the advantages and disadvantages of using a Darlington transistor is also presented as well as the schematic of a simple Darlington based voltage regulator. The documents for this tutorial can be found on TheSignalPath.com
Watch the video here: [54 Minutes]
http://thesignalpath.com/blogs/2013/07/21/teardown-and-repair-of-an-agilent-e4421a-synthesized-signal-generator/
More videos at TheSignalPath:
http://www.TheSignalPath.com
mikeselectricstuff:
A more detailed teardown of a similar unit :
KedasProbe:
During the video I was thinking what I would do next.
Adding the power supply on that point that I would not have dared to do. (without schematic)
Do you have an idea about why the darlington failed after probably a long time?
"cat scan" :) don't go in the joke business though :)
SeanB:
The darlington probably failed because of inadequate heatsinking. It is providing a 1.5A load from a 12V rail and is dissipating around 5W of heat. The die probably is running at around 120C, which is not good for long term reliability.
A new thermal pad and a top of case extra heatsink, or mount a bigger heatsink in the case near it and use 3 flying leads to connect to the board would be a lot better solution. It would be interesting to measure the temperature of the device after it has been on and with the case closed for 20 minutes, it probably will be at a case temp close to 70C, and inside will be more.
kg4arn:
--- Quote from: SeanB on July 21, 2013, 01:44:58 pm ---The darlington probably failed because of inadequate heatsinking. It is providing a 1.5A load from a 12V rail and is dissipating around 5W of heat. The die probably is running at around 120C, which is not good for long term reliability.
A new thermal pad and a top of case extra heatsink, or mount a bigger heatsink in the case near it and use 3 flying leads to connect to the board would be a lot better solution. It would be interesting to measure the temperature of the device after it has been on and with the case closed for 20 minutes, it probably will be at a case temp close to 70C, and inside will be more.
--- End quote ---
Do you guess that it is a fundamental design flaw or is one of the boards faulty and drawing excessive current?
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