Power adapter for Hercules speaker system DOA.

[David Farber]

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.
--
David Farber
Los Osos, CA

[Phil Allison]

** 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

[mrob...@att.net]

David Farber <farberbe...@aol.com> wrote:
> The problem is that the 16 volt 1.4A power adapter is not working.

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

[David Farber]

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.

[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.

[John-Del]

On Monday, February 15, 2016 at 3:51:05 AM UTC-5, mrob...@att.net wrote:

> 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.

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

[Uffe Bærentsen]

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

> 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

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 :-(


--
Uffe

[David Farber]

Hi Uffe :-)

My sticker comment was meant to be taken as sarcasm.

[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!