Power Supply Pinout
Same for 8550 (94 W), 8570 (132 W) and 756x (180 W).
Top row, odd numbered pins, left to right: 1-49
Power-off the system. Remove power supply and place it with connector
facing up. Power-on the power supply and check for voltages listed below. If
voltages are not correct, check the power cord for continuity. If power cord is
good, replace the power supply.
Sometimes AC power cords develop a set in the plug
contacts so that there is intermittent or poor contact
with the AC receptacle pins in the PSU. Try reseating or
swapping out the AC cord.
Note: If you have a dead PSU with no voltages, suspect F1 or F2 have blown.
8550/Z PSU Specs
MODEL NO.: AA13621, IBM P/N: 90X9527, IBM FRU P/N: 90X9366
Max continuous output power is 94 W.
No side blower. The blower plugs into the motherboard, is
supported by two plastic snaps to top rack, and it blows out the rear of
the 50/50z unit. Bottom of power supply does not have a screen, it has finely
punched holes, 11 or 10 holes across, the length of power supply.
8570 PSU Specs
ASTEC Model AA15530, IBM P/N 90X9409, IBM FRU 90X8626
Max continuous output power is 132 W.
7561/62 PSU Specs
Plessey (Italy), IBM P/N 33F5202, IBM FRU 57F2728
Input 95-120 V @ 3.6 A 50 - 60 Hz, 200 - 240 V @ 1.9 A 50 - 60 Hz
Battery Charger 26 V DC @ 40 mA
This PSU has an external, two pin Molex connector that provides power to the case fan. There is a 9.25"Wx1.75"H inch hinged cover on the lower outer side of the PSU. It is fastened at the front by a single captive standard screw. The cover pivots open on the rear hinges, revealing a three pin Molex power connector, like a female drive power connector. The battery cavity is 1.875" deep.
Remove the Power Supply (8550 / 50z / 70 similar)
Remove the two screws at the back of the case. Remove the screw at the front inner corner. Pull PS out from planar.
Power Supply Cleaning
8550 / 50z PSU (No Built-In Fan)
The way the 50 / 50z PSUs were built, they
have a screen across the bottom side. Just like on a
clothes dryer, you have to remove "lint" from the
screen. I used a T-10 security Torx to open it.The fan
is a Panaflo DC Brushless, Model FBH-09A12L, 12V 0.14A
or a Nidec Beta SL Model D09B-12PLL 12V 0.09A
8570 PSU Removal and Cleaning (Built-In Fan)
Remove the standard screw at the front of the PSU. IBM
even put a nice access hole through the drive shelf so
you can get to it while the system is assembled.
To undo the mating clam shell, note the retaining rib
top center. Use a small screwdriver to get under the
sheetmetal and pull the halves apart. The inner cover
with the fan pivots on tabs at the lower inner side.
The fan is still connected to a power tap. Pull the
cable straight out and the fan/cover is now free. Put
I had a dust bunny about the size of your pinkie, jammed
under a cable... Dust coated about half of the
components. Can of cheapo Radio Schlock computer duster
cleaned off the components, although I had to stop and
let it warm up before proceeding...
You can pivot the edge connector out of the bottom
edge of the PSU by SIMMply pulling UP at the rear of it,
and then BACK on it.
Oddly, the two security T10 screws on the black plastic
only seem to tighten the connector onto the post,
leaving the edge connector free to move in four
directions, but it's mounting does not allow it to pull
out or be pushed in. Makes sense, this allows for
greater freedom during automated assembly.
Once you pull the edge connector free, you will see F1 and F2 in the lower left corner of the PSU PCB (toward the AC socket). The power supply has TWO fuses, one on the Hot, the other on the Neutral. ASTEC called it "Double Pole / Neutral Fusing". ASTEC part number is ASTEC 084-00300030-0217. It is a BEL 3AG, 5A 250V Fast Blow.
Current BEL product is 3AG 5-R 3AG is a 6x32mm cartridge form. Datasheet HERE.
8570 / 8550 Bus Riser Power Hack
You will need:
It is a good idea to leave the cables on the power connector as long as possible to make it fit on either direction a hard-disk can be installed in a Model 50 or 70.
Please note that clone PC power cables use yellow/black/red, while IBM systems use yellow/black, or red/black/blue. What is important is the position of the conductor. Note that the drive power connector is keyed with beveled edges.
Raiser Card FRU 90X1111
J1 (JN1) Floppy 1 (A:)
The three resistor/capacitor pairs on the riser are for DC-buffering and decoupling. The earlier risers lacked them and once you'd stuffed in 2 FDDs or 1 FDD and a tape problems occurred with loss of data during copying and suchlike.
What to do:
Warnings and recommendationsThe maximum power from this hack is about 5 V / 1 A and 12 V / 1 A so if you have both disk-drives or one disk-drive and a tape-streamer installed ... it is probably not a good idea anyway. It will -nonetheless- work in most cases, until the unit driven over this port doesn't take too much power. Most modern Harddisks will not exceed these limits. In case of doubt: consult drive manual for its power-consumption. Or don't do the modification.
If you have only one disk-drive installed, take the connector of the second drive for modification. Caution!! Take care not to damage the tiny connections on the board near the connector for Drive 2 while soldering the wires.
Remember, that the Mod. 50 / Mod. 70 power-supplies aren't that powerful at all.
Especially the Mod. 50 power-supply (94W!!!) is known to have lesser power than assumed. If you'd already installed a -386/-486 upgrade, 64Megs of RAM, SCSI-adapter and a Hi-Resolution graphic board it will surely collapse.