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On Sun, Aug 5, 2018 at 11:50 AM, Vincent Trouilliez wrote:

On Sun, Aug 5, 2018 at 12:38 AM, satbeginner wrote:

I had a quick look on the 2232 schematics
The 2232 has a full wave rectifier (CR965 & CR967 coming from pin 20 and 22

of the transformer)

That's true for the early units, which drive the fan at 8.6V via the a middle
tap and the two +/- 8.6 rails.
But I see there was a different wiring for later 2232's : this time it's
running at a slightly higher voltage : 10V. It's across the +/- 5V rails and
doesn't use the middle tap/ground, hence a 4 diode bridge.

I don't know why they changed the wiring. Either they felt they needed a bit
more voltage and/or they decided that running a noise factory such as a fan,
from the 8.6V rails that power the sensitive analog stuff, was far from ideal,
even though the fan is wired upstream of the LC filtering networks.

and a capacitor C965 and a current limiting resistor R965 installed to power

the additional fan.

At least this bit is common to both designs...

Based on the empty room on my 2215A PCB it looks like they only planned a

half

wave rectifier?
There is room for 1 diode coming from pin 20 of the transformer, 1 capacitor
and 1 resistor and a 2-pin connector for the fan.

OK ! So yet another wiring arrangement ! LOL

So in short... in all cases they put that 2.7ohm resistor in series, and that
big 4700uF cap across the fan... but as far as voltage source goes, you pretty
much tap the secondaries in any way that you see fit, so long as you tap
straight from the transformer pins so that the crap/electrical noise from the
fan can still be filtered downstream by the LC PI networks, and keep the
delicate analog stuff of the scope happy.

Well that's how I understand it so far...

Will try this,

Yes, keep us posted, and take some waveforms and measurements to see how this
crude single wave rectification performs... and of course measure ripple
before/after the mod, to make sure it's still within specs ^^


Regards,

Vincent Trouilliez

Un saludo,

Leo

Hi Vincent,

I took some pictures of the empty spaces on my PCB and how I filled them with the three components and the connector.
The pictures and the additional schematics are added to my album /g/TekScopes/album?id=64919

For now I cannot measure any (extra) ripple because I do not have the fan yet.. :-)

To be continued,

Leo