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Registered Member #326
Joined: Sat Mar 18 2006, 01:12PM
Location: Glasgow, Scotland
Posts: 66
I've currently got a dead Dell Inspiron 510m laptop in bits on the bench. Input is 18V DC from an external PSU. The input goes through what looks like a common-mode choke, the positive side of which presents an impedance of meghoms and hence appears to be faulty. The negative side is OK.
Not being an expert on SMPS, I'm wondering whether its safe to try shorting the positive side of the choke. Most SMPS have some sort of inrush suppression (e.g. NTC resistor), there doesn't seem to be any such protection obvious here, although it is fed by another SMPS with an amp or 2 of maxiumum output, rather than the mains.
My other thought is whether this is the primary fault, or whether it's failed as a result of a fault in the laptop's PSU that has drawn an excess current?
Registered Member #139
Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358
Be careful messing with Dell PSU's, not sure if you are aware, but there is actually 3 electrical faces on the plug. The outside of the "cylinder" of the plug is -, the inside of it is +, and the pin in the centre is + for charging the battery.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
That choke is probably just to make it meet EMC regulations. I reckon it should work fine shorted. As for whether it was burnt out by excess current draw, you'll find out soon enough >_<
Registered Member #326
Joined: Sat Mar 18 2006, 01:12PM
Location: Glasgow, Scotland
Posts: 66
Thanks guys. It works fine with the choke shorted.
Be careful messing with Dell PSU's, not sure if you are aware, but there is actually 3 electrical faces on the plug. The outside of the "cylinder" of the plug is -, the inside of it is +, and the pin in the centre is + for charging the battery.
This PSU's slightly different, it has the plug you describe, but the centre pin is a data line to detect a genuine Dell PSU, part of another sinister ploy to force you to buy their overpriced spares.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
That's insane
Although I suppose it would be of some use if it protects your laptop from being plugged into the wrong PSU
I recently had to repair a laptop which someone had gone and plugged into a random wall wart, dismantling a whole laptop and solding a tiny SMT fuse was not fun
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Watch out, those chokes are part of the suppression system. Taking this out means high frequency noise from the PS can get into the laptop, potentially causing instability.
I'd replace the choke unit if possible, or solder in a homemade replacement with sufficiently thick wire on a former.
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Dell Inspiron Laptop PSU/Filter Problem
