> ... 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.