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On Giovedì, feb 17, 2005, at 02:57 Europe/Rome, David Clarke wrote:
> > ... At startup, sometimes about 90 % of all leds are on,
> > but is not possible to change any parameter. Sometimes,
> > after a couple of secs goes ok.
> ...
> > I'm suspecting that the DC OK signal sometimes is not up
> ...
> > I'm getting
> > a maximum DIGITAL DC +4.2 (maximazing the trimmer, 4.01 at minimum
> > position). I have the second type board (so no trimmer for the DIG OK
> > signal)
>
> If this is actually the output of the 5V digital line that you're
> reporting,
> then that would seem to be the source of the problem (i.e., 4.2v is .6
> or .7
> volts too low for good operation - and per the docs, you should be up
> at 5.0v).
>
> The solid-on LED indication would indeed likely be due to the DC OK
> signal
> never getting up there (since the power supply is struggling to get to
> a point
> where the 5V is "ok."
>
> If the voltage is really that low too - then other system operation
> would also
> be questionable.
>
> > Do you think is the LM350k or is the power coming in that is too low
> ?
> > and what would be the correct incoming voltage from the transformer?
> > Can be the low voltage caused by old lytics caps ?
>
> I wouldn't immediately expect the electrolytics, but I would certainly
> look at
> the input voltage to the LM350 to see what sort of levels you are
> seeing. If
> you can, it would probably be good to look at this with a 'scope.
>
> While the circuitry between the old and new PSUs are different, I
> would still
> expect to see the same order of magnitude of voltage going into the
> voltage
> regulator - so that'd be about 13V coming in, with a ripple frequency
> of 120Hz.
>
>