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Power adapter for Hercules speaker system DOA.

I was given a Hercules XPS 2.140 Slim speaker system. The owner purchased it new from Amazon and it never worked. It sat around longer than the return period so I inherited it. The problem is that the 16 volt 1.4A power adapter is not working. I cracked open the box and could not find any obvious faults. In circuit, the 68uF 400V filter cap charges to the peak line voltage but that's about all that is happening. I cannot measure any oscillation at the MOSFET. I removed the MOSFET from the circuit and did the quick DMM check where you put some voltage on the gate and drain and then check the resistance between the drain and source. That test passed. The D-S resistance went down to two ohms.

I removed the switching transformer and took these measurements: Primary winding that goes to the MOSFET: 0.3 ohms DC. Then I used my ESR meter on the primary windings and it measured 32 ohms. There is another primary winding (at least it's on the same side of the transformer as the winding that goes to the MOSFET and I think it feeds back to the controller) that measures:

0.4 ohms DC The ESR meter measures open circuit. I used my Bob Parker LOPT tester and it actually lit up all the lights when applied to these windings.

The secondary measure 0.4 ohms DC and 7.3 ohms with an ESR meter.

I was wondering if anyone can figure out if these measurements mean anything or is there a better method to test this.

Thanks for your replies.

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David Farber 
Los Osos, CA
Reply to
David Farber
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** What you have is a small SMPS that likely has never worked.

Full of SMD too - right ? Worth about $10.

All repairers RELY on the fact that items used to work - therefore there is NO need to search for wrong parts, missing parts, parts incorrectly installed, missing or incorrect wiring or PCB connections between parts.

When an item has been tampered with or there are signs of attempted repairs, most techs refuse to touch the job - because of the same issues.

OTOH, you have to look for all of the above with an item that is damn near repair proof by design.

... Phil

Reply to
Phil Allison

Triad WSU180-2000, 18 V 2.0 A, new, $21+shipping at Digi-Key. HP 0957-2257, 18.5 V 3.5 A, used, $6.50+shipping at All Electronics.

Downside: you have to figure out how to get rid of a couple of extra volts. Running it through a couple of 1N5400s is probably close enough.

Triad WSU150-1600, 15 V 1.6 A, new, $15+shipping at Digi-Key.

Downsides: Probably won't allow the speakers to go as loud as the original power supply. There is a small but nonzero chance that the speakers won't work at all on the lower voltage.

To me, the more interesting part is the circuitry inside the speakers, which manages to perform a miracle: 32 W "RMS" audio power output from a

22.4 W power supply.

Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

Reply to
mroberds

Hi Phil,

All very good points about repairing something that never worked. However I did forget to say that there is a QC PASSED sticker on it so it *had* to be working when it left the factory. :-p

Thanks for your reply.

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David Farber 
Los Osos, CA
Reply to
David Farber

Hi Matt,

Thanks for the good research! I'm tempted to order a MOSFET for a few bucks and see if that fixes the problem. I remember back in the VCR days I had a particular problem with a dead unit. The switching power transistor checked good but I could not find any other faults so I remember ordering an SK replacement for it because my local store didn't have the original part. That didn't work either. I had to special order the original part before it would work.

Regarding your observation about power comparison vs. power output: Did you ever work in a hifi retail store when they were on every street corner in the 70's and 80's? Numbers were constantly generated out of thin air. The fact that they now put it in writing probably means that less people can do the math now than 40 years ago.

Thanks for your reply.

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David Farber 
Los Osos, CA
Reply to
David Farber

It probably could do 32 W for a split second while the secondary caps discharge..

Reply to
John-Del

Den 15-02-2016 kl. 19:26 skrev David Farber:

That sticker only indicates that someone at the factory have the task of putting the stickers on. It does not indicate that the unit has been tested :-(

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Uffe
Reply to
Uffe Bærentsen

Hi Uffe :-)

My sticker comment was meant to be taken as sarcasm.

Thanks for your reply.

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David Farber 
Los Osos, CA
Reply to
David Farber

I did order a replacement eBay MOSFET and it didn't help. Now that I've just read the S.E.R. thread about "Fake Chips," maybe that didn't prove anything!

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David Farber 
Los Osos, CA
Reply to
David Farber

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