small psus free to good home

On Sun, 28 Feb 2010 16:02:59 +0000, Java Jive
wrote:

I've removed the PSU from the Pace Twin now. Output as measured by my
multimeter is all over the place, rather than being a steady voltage,
so I presume I am correct in assuming it's defunct.

It's a labelled module:
Model: DPSN-36BP A REV:00
SN: RCT0243000553
There are two outputs marked, +18V and +13.25V, the latter and the
Ground are those actually connected to the Twin. Any knowledge or
suggestions?

On Sun, 21 Feb 2010 16:08:31 +0000, Java Jive
wrote:

Does anybody know what the PSU rails of a Pace Twin should supply?
Mine has just died, and I'm pretty sure it's the PSU. My guess is
it's 5vDC.

Your Pace Twin power supply may well be broken, but before you go to
any expense to fix it, are you aware of the problems all Pace Twin
owners have been having since December with a powering up problem if
tuned to ITV.

See
http://www.digitalspy.co.uk/forums/s....php?t=1185249
& the official view at
http://www.pace.com/corporate/conten...ullid=TWIN_PVR

If your power is up the creek, you might be able to pick up a cheap
unit for spares on ebay with people selling because of the above
mentioned problem.

David

On Sat, 27 Feb 2010 17:38:45 +0000, Java Jive
wrote:

Yes. Some beaches on pacific islands are piled high with plastic
flotsam washed ashore, but the worst thing of all is what happens to
seabirds such as Albatrosses. Apparently they have evolved over
millions of years to believe that anyone of a particular size and
shape floating on the sea is food, so they swallow pens, toothbrushes,
ink cartridges, etc, and then regurgitate them for their young, which
of course die.

There's another thing, those sodding electric toothbrushes which die
and leave you with a bunch of new heads that don't fit the
replacement, for which you buy some more heads, rinse and repeat

In article , Java Jive
wrote:
Tried to post this before, but it seems to have gone into a black hole.
Apologies if anyone receives it twice.

On Mon, 01 Mar 2010 13:45:17 +0000, Java Jive
wrote:

Yesterday, in an idle moment, it occurred to me to try powering the Twin
from the 12v DC supply rail of a PC peripheral connector, such as is
used to power DVD-ROM drives, etc (I have a spare PC PSU which works but
is now outdated), so I retrieved the wreckage from the cupboard and
connected up ...

So I now have it powered up

... and everything works just fine except ...

but there is an unacceptable buzzing on sound

... this is now a howling noise. I don't have a means of measuring
frequency except my guitar tuner, which makes it a very sharp A#,
occasionally flipping into D#, but mostly the former.

Any thoughts or suggestions as to what could be causing the noise?

Only the obvious:

A) That the '12VDC' is lousy with variations at those frequencies. Either
caused by the PSU being a nastly switch-mode type - or something else that
it is driving (if it is driving anything else).

B) The Twin is motor-boating against the PSU.

C) The PSU expects to deliver higher current and has a sensor circuit that
is dithering about if it should be 'on' or not.

D) The Twin wants 13V not 12.

E) As per (C) but the Twin is demanding too much current, not too little.

Have you tried a capacitor across the rails *at* the Twin? And/or a shunt
resistor to draw more current? Can you measure the voltage and current?

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Java Jive
writes

Any thoughts or suggestions as to what could be causing the noise?

1) the psu is underloaded and the outputs are all over the place. Stick
a couple of disk drives on the outputs and see if that helps.

2) it's a cheap piece of **** which is poorly RFI shielded and the Twin
is picking up the switching (chopping) frequency on the primary side.
Could be anything between 30KHz - 100KHz depending on load, which would
explain why you are hearing variations in tone.

--
(\__/)
(='.'=)
(")_(")

In article , Java Jive
wrote:
On Thu, 19 Aug 2010 16:31:30 +0100, Jim Lesurf
wrote:


B) The Twin is motor-boating against the PSU.

Que?

Sorry, Jargon of the type beloved of engineers. :-)

'Motor-boating' is a term that I guess was applied because some systems
made a sort of 'put put put...' noise when it happened.

The process is a form of bias instability.

Consider a circuit that happens to draw much more current when the rail
voltage is above a given voltage than at a slightly lower voltage. Then
drive it with a PSU that struggles to provide the current demanded.

When you switch on the system powers up. Until the rail hits the 'magic'
voltage the PSU can cope. But when the amp suddenly demands more current
the PSU can't cope and the rail voltage falls. Once it falls below the
magic level the current demanded reduces and the PSU can cope, so the
voltage rises again... repeat until bored. The parts of the system take a
finite time to react to changes, so you get a looped behaviour with a given
repeat frequency. :-)

In effect, a relaxation oscillator. It tends to require a combination of
non-linear behaviour and some suitable reactances in combination. It can
arise in various ways, and generate any old frequency depending on the
details of the system.

The behaviour is actually exploited in oscillators at frequencies up to
100GHz and above. :-) But was probably first noticed with audio and LF
systems many decades ago, producing variations at low frequencies. Hence
the name.

Have you tried a capacitor across the rails *at* the Twin? And/or a
shunt resistor to draw more current?

No, but I might give that I try when I've got a moment.

If a cap just reduces the frequency then it is probably motor-boating.
Alternatively it may stabilise. Note I'm assuming the PSU is current
limited to protect it against current surge demanded at turn-on. But that
might mean it refuses to start if the capacitance is too big.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

"Java Jive" wrote in message
...


.... this is now a howling noise. I don't have a means of measuring
frequency except my guitar tuner, which makes it a very sharp A#,
occasionally flipping into D#, but mostly the former.


Also, it could be the fan. Plain bearing fans do sometimes squeal or "sing"
when they are dry, and a bit worn. Another thing they do is make a
continuous random chattering noise, uncannily like a failing hard disk.

Of course, I agree it's more likely due to the PSU operating below it's
minimum load (after all, it's supposed to be fastened to a motherboard), but
it might be worth looking at the fan.

SteveT