Instructions to change a Power Supply

The Power Supply (PS) of a DIRC Wiener CRate (WCR) is located on the back of the crate. It is cooled by the three (unfortunately non-bypassable through epics, design feature) fans which are located on the back of the fan tray.

Power supply in a DIRC Wiener crate

Power supply outside the Wiener crate

The first failure of a DIRC PS occured on Tuesday 09/27/05 (owl shift) after almost 6 years of running w/o problem. We lost connection with the WCR in sector #9 (white epics channels) and couldn't communicate again with it. Therefore, an access with the opening of the backward east door was requested which was unfortunately delayed by one day for lack of manpower. While we were waiting for the acess, we investigated the problem and a power supply failure was among the 4 favoured hypothesis:

power cord / power failure;
broken non-bypassable fan;
melted PS fuse;
PS failure.

We prepared all the hardware needed to fix any of these problems which allowed us to minimize the controlled access time (~ 55' in total). The reliability of our PS for the next years will be investigated. The second failure was sector #6 on 10/5/06 when the Wiener crates were turned back on to do some tests during the down. Sector #6 shut itself off and was blinking "+5V low voltage". The crates were set to normal mode the week before after running for the past seven years in normal mode which may be why the PS hadn't tripped before. The exact cause is under investigation.

Although the change of a PS is not technically difficult, one should be very cautious when doing this for two main reasons:

the PS power cord MUST be unplugged before working on it;
the PS is quite HEAVY, which may lead to Safety issues given the various orientations of the WCRs around the DIRC.

Therefore, Matt McCulloch (our DIRC technician) is the right person to perform such replacement. One should not hesitate to contact him!

To remove the PS from the WCR, one just needs to unscrew the two black screws located at the top-left and at the bottom-left -- see all 4 pictures for details. One should also be cautious not to damage the connections which are visible on the crate below the PS. They are normally protected but one needs to be smooth when moving carefully the PS in and out.
Before doing this, it is worth checking the PS fuse one can access by opening the black disk located close to the power cable connection. The 20 Amp fuse can be tested using a meter and Ray Rodriguez is keeping new spares in one of his cabinets.

Back of the power supply: power cord, screws and fuse are visible

Picture of the back of a Power supply showing the wire connections

Back of the power supply showing the wire connections behind the metal plate.

Zoom on the back of the power supply. In this picture, the power cord has been unplugged.

Web Page created by Nicolas Arnaud
Last updated on October 6th, 2006 by Brad Wogsland