G/Clink Voltage Regulator Modification Procedure

PLM  4/27/04

First obtain a copy of the modified schematic fpowera.ps at:
http://www.phenix.bnl.gov/phenix/WWW/publish/leitch/mutrfee/lv_regulator_2004/
which has a revision date of March 26, 2004. This schematic
shows four new diodes, D6, D7, D8 and D9, of type 1N4148.
These diodes are added between the 5 V fault line and pin 4
of each of the four 5 V regulators, type MC29501-5.0BT. They
serve to pull the 5 V fault line low (thus turning off the
3.3 V regulator) if any of the loaded 5 V outputs are off.

Next print a copy of the photos that Mike Leitch took of
a regulator board that I had previously modified. See
lv_reg1.jpg and lv_reg2.jpg at :
http://www.phenix.bnl.gov/phenix/WWW/publish/leitch/mutrfee/lv_regulator_2004/
These photos show how the diodes are mounted and where the
the insulation is placed.

The diodes are installed with the non-banded end soldered
into a via that carries the 5 V fault line (above the "F"
of the white 10UFD label in the photos). I found that the
easiest way to do this was to remove the solder which fills
the via using a vacuum type desoldering tool. Then form the
right angle bend in the diode lead. Finally, using the
soldering iron to heat the diode lead and via, slide the
diode lead into the via and solder it in place. The lead
is a tight fit in the via.

The banded end of the diode is attached to pin 4 of the 5 V
regulators (which is connected to the banded end of the
10 UFD capacitor). A short piece of teflon insulation is
placed on this lead of the diode to prevent a short to pin
5 of the regulator, as shown in the photos. Wrap the bare
part of the diode lead around pin 4 and solder it in place.
Using an ohmmeter across the diode connection, with the
negative lead on the banded end, check that the diode
conducts. With the ohmmeter leads reversed, the diode should
not conduct.

It's probably worth testing each modified board with the
test setup and procedure we devised previously. Mike Leitch
will supply those instructions.