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Specifications
Remove the Power Supply
Open the PSU
Power Systems Checkout
Drive Connector 1
Power Supply Connector P1
Power Supply Connector P2
Specifications
FRU P/N 49G2688
Input:
115 V / 4 A, 220 V / 2 A
Output:
+5 V / 11.0 A
+12 V / 2.4 A
-12V / 0.3 A
8-20 V / 2.5 A
The 8-20 V is for charging the 700/720 battery
Total power:
147.4 W Max
Remove the Power Supply
This threw me for a loop, but I eventually pegged onto it. Undo the three
captive thumbscrews at the rear of the 3550, remove the bezel. Remove the top
by pushing it forward about an inch, then lift up (like a 50/70/90). Unplug any
device in the 5.25" bay. Pull off the right side of the spring bezel by pulling
straight out. Unplug P1 and P2 on the right side of the planar. Move all three
cables to the front so you can pull them through the enclosure.
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Important: Remove the two phillips screws along the
lower outer edge of the PSU (on the die cut extensions) and remove the single
phillips screw from the upper right corner above them. This single screw will
stop you!
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Look at the back of the case. Notice the two black angles sticking out, and
immediately below them, a catch. Lift up on each catch and slide the PSU out of
the case. It's loose enough so you can undo one side, push the PSU out a bit,
then undo the other catch, then slide the PSU out.
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Open the PSU
See above to remove the PSU from the case. Now sit and try to figure out how
is this going to work? A VERY important point. Look at the "step" right above
the cable outlet. See that small phillips screw right next to the inner
vertical edge? You must remove that screw, because it fastens a heatsink from
the PCB to the case. Remove the two T-15 security TORX at the front lower edge
of the PSU.
Look at the upper rear edge of the PSU case. Note that the upper piece of
the PSU case is hooked under the back edge. Pry the upper piece forward until
it clears the retaining lip. Now rotate the upper piece forward on the wire
bundle for the power conductors only about an inch. Now twist the cover towards
the side of the wire bundle so it can uncover the PSU guts.
Power Systems Checkout
If the "power good" light is not on and if the power-supply fan is not
running, check the power cord for continuity and proper installation.
If the power cord is not the problem, either the power supply is defective
or another component is defective and is causing the power supply to shut off.
To verify that the power supply is operating correctly, do the following:
- Power-off the 3550 Expansion Unit and disconnect the 3550 Expansion Unit
power cord.
- Remove all power supply connectors (power supply connector P1, P2 and drive
connector 1) from the system board of the 3550 Expansion Unit and SCSI
device.
- On power supply connector P2, short-circuit pin 4 to pin 6 and
short-circuit pin 7 to 8.
- Connect the 3550 Expansion Unit power cord.
- Check the power supply voltages using the figures on the next page.
Drive Connector 1
Standard 4 pin molex
| Pin |
Signal |
V dc Min. |
V dc Max. |
| 1 |
+12 V |
+11.52 |
+12.6 |
| 2, 3 |
Ground |
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| 4 |
+5 V |
+4.8 |
+5.25 |
If any of the voltages are not correct, replace the power supply.
If all voltages are correct, the power supply is working properly. Another
3550 Expansion Unit component might be causing the power supply to shut
off.
Power Supply Connector P1
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| Pin |
Signal |
V Min |
V Max. |
| 1, 2, 3, 4 |
+5 V |
+4.8 |
+5.25 |
| 5, 6, 7, 8, 10 |
Ground |
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| 9 |
+20 V |
+19.0 |
+21.0 |
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Power Supply Connector P2
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(*see Possible Error In HMM below)
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| Pin |
Signal |
V Min. |
V Max |
| 1, 2 |
+12 V |
+11.52 |
+12.6 |
| 3 |
Power Good |
+4.0 |
+5.25 |
| 4 |
On/Off Signal |
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| 5 |
-12 V |
-10.92 |
-13.2 |
| 6, 7 |
Ground |
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| 8 |
Global Signal |
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Possible Error In HMM
John Seniura wrote:
Just a correction for an error in the IBM HMM for the 3550
expansion unit.
To check out the power for the expansion unit, you have to short some pins
on the P2 connector from the power supply. The diagram in the HMM has the pins
numbered backwards. I discovered this just before I was about to throw out my
expansion unit because the power supply appeared to be totally dead. On a
hunch, I tried shorting the pins in the opposite direction and I got good
readings for all voltages.
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