Hello,
I am trying to repair a Logitech LS21 multimedia speaker system (Model Number S-00042).
There is a small switched-mode PSU which I have opened up inside the main sub-woofer unit. The soldered inline mains fuse was blown.
There was some blackening around a few surface mount resistors. There is a short across the Drain-Source of the MOSFET transistor (WFF2N60).
Should I just replace the transistor and fuse or there likely to be some other cause?
hi, often when the main mosfet transistor is blown, alsoone or more diode(s) of the bridge get shorted too you must verify that. and also when the mosfet gets shorted it's often because the main capacitor has heated and has too much esr - you should measure it and change it if needed. hope this helps.
Thanks for your reply Kripton. I do not own an ESR meter. Will the capacitance range on my multimeter give me an indication that the capacitor has been damaged?
often when the esr is too high, the capacitance changes also but not always. so you can measure the capacitance and if it is really out of spec change the capacitor in my signature below, on my web site there are easy to build esr meter
- build one it is always handy to have an esr meter when you fix electronic stuff.
Last option:
Quarta-feira, 3 de Abril de 2013 21:30:12 UTC+1, M. Joshi escreveu:
I had the same problem. After reading a lot on line about this specific pro blem in this model, I gave up, because there isn't any pcb spares for this and it is just impossible for me to know what is the resistance value of th e burnt ones, because they are burnt!!! Well, I have loads of AC DC transfo rmers lying around the house... I guess I kind of collect them... and as th e problem is in the internal current transformer, I just replaced the inter nal burnt one, for an external that I just had Lying around. Cost... NOTHIN G!!! works perfect. I tried a 12V- 1A out... Stop wasting time looking for the resistances... I lost hours, and i am sure my fix will work for years to come! Hope this helps you out! Ana
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