The fuse strip located near the hinge on the OEM supply door routes the +5, +15, and -15 voltages from the OEM supply to the card rack unit motherboards.
Each card rack unit has a dedicated section of fuse strip and specific fuse values.
When troubleshooting problems with card rack units it may be necessary to test the fuses in the fuse strip. With the card rack power OFF you can visually inspect each fuse to see if any of them look like they are blown. You can also use an ohmmeter to measure the resistance of the fuses (typically one ohm or less). In some cases it is helpful to measure the actual voltage on the fuses. It is possible that a fuse that looks good is actually blown. Or the voltage on the fuse may be loading down on the output side.
Since the +5, +15, and -15V OEM supply outputs are floating with respect to ground, you need to reference your meter to the correct place in order to measure the voltage. The card rack power needs to be ON when measuring the voltages on both sides of the fuses. The voltage should be very close to the same value on both sides of the fuses. One side is voltage in, the other side is voltage out to the card rack unit.
The picture below shows the correct OEM supply reference point for the +5V, -15V, and +15V fuses.
For example, to measure the middle section -15V fuse you would need to put your DVM red lead on the left side of the middle fuse, and the black lead of your DVM to the CH3 white wires on the OEM supply. Then also measure the other side of the same fuse. The voltage on both sides of the fuse should be very close (within a few millivolts). Note that you may need to remove the protective plastic cover on the fuses in order to be able to measure the fuses.
There are up to 13 sections on the fuse strip and each section is typically dedicated to a particular card rack unit motherboard. Keep in mind though that the fuse locations are not written in stone and so units on your system may be plugged into other fuse sections. Also, some units are removed when an RBD software upgrade is installed. When in doubt, trace the power cables from the back of the motherboard to the fuse strip.
The fuse values (in Amps) and locations are shown below:
5400 XPS
| Section | Unit | Top +5V | Middle -15V | Bottom +15V |
| 1 | 72-488 | 10 | – | – |
| 2 | 71-205 | 5 | 5 | 2 |
| 3 | 72-250 | 3 | 1 | 1 |
| 4 | 72-490 | 10 | 5 | 5 |
| 5 | 72-030 | 1 | 1 | 5 |
| 6 | Not used | |||
| 7 | Not used | |||
| 8 | 80-360 | 5 | 5 | 5 |
| 9 | 77-067 | 2 | 2 | 10 |
| 10 | 72-360 | 1 | – | 1 |
| 11 | Terminator | 1 | – | – |
| 12 | Not used | |||
| 13 | Not used |
5600 XPS
| Section | Unit | Top +5V | Middle -15V | Bottom +15V |
| 1 | 72-366 | 1 | 1 | 1 |
| 2 | 80-365/366 | 5 | 5 | 5 |
| 3 | 72-030 | 1 | 1 | 5 |
| 4 | 71-205 | 1 | 2 | 1 |
| 5 | 72-488 | 10 | – | – |
| 6 | 74-500 | 10 | – | – |
| 7 | MCD Preamp | 1 | – | 1 |
| 8 | 81-175 or 73-080 | 10 | 2 | 2 |
| 9 | 74-062 | 10 | – | – |
| 10 | 97 or 72-100 | 1 | 2 | 5 |
| 11 | 73-070 or 73-080 | 5 | 2 | 2 |
| 12 | 73-057 | 3 | 3 | 3 |
| 13 | 72-700 | 1 | 1 | 1 |
650 / 660 AES
| Section | Unit | Top +5V | Middle -15V | Bottom +15V |
| 1 | 79-170 or 81-175 | 10 | 2 | 2 |
| 2 | 74-062 | 10 | – | – |
| 3 | 72-150 / 96A | 5 | 5 | 5 |
| 4 | 74-500 / Term | 10 | 0 | 0 |
| 5 | Not used | |||
| 6 | Not used | |||
| 7 | AES 72-100 / Term | 3 | 2 | 5 |
| 8 | 97 SED / 72-100 | 1 | 2 | 5 |
| 9 | Not used | |||
| 10 | 72-105 | 1 | 2 | 1 |
| 11 | 72-600 | 2 | 1 | 1 |
| 12 | 73-057 / Term | 3 | 3 | 3 |
| 13 | 77-072 | 5 | 2 | 2 |
Here is an example: Lets say you want to measure the voltage on the 80-365 fuses on a 5600 XPS system. You would first locate the correct fuse section, in this case that is section 2. The top fuse in section 2 is the +5V supply and so you would measure from the left side of the top fuse in section 2 to the white ground wire on Channel 1 (the big lugs) on the OEM supply. Then you would also check the other side of the same fuse to make sure that you have the same voltage on both sides of the fuse. The middle fuse in section 2 is the – 15V fuse and it is referenced to the white wires on Channel 3 on the OEM supply. Finally, the bottom fuse is the +15V and it is referenced to the white wires on Channel 2 of the OEM supply.
By using the correct reference point you can easily measure the voltages on both sides of the card rack fuses when troubleshooting electronic problems with your older PHI XPS or AES system. As always, refer servicing to qualified personnel. The OEM fuse voltages are considered low voltage. However, most of the card rack units themselves generate high voltages and should be only worked on by technicians with the proper training to work safely with high voltage. If you need help troubleshooting a problem with your XPS or AES system, contact RBD Instruments for assistance.
