Ardent Tool of Capitalism

PC720 Power Supply

Specifications
Power Supply Connectors Pinout
   Planar Power Connectors P1/P2
   Planar Power Connector P9
   Planar Power Connector P11 - 3.3 V
   Riser Power Connector P10 - 3.3 V
Power Supply Fan

Content created by Tomáš Slavotínek and Tatsuo Sunagawa.

Specifications

The PC720 power supply is a compact unit with some relatively modern features. It has a low-voltage power switch (known from later PS/2 and PS/55 machines), a stand-by 5 V supply and a 3.3 V rail. The integrated fan has an automatic speed regulation.

Power Consumption

Maximum: 70 W
Typical: 40 W

PSU Model

Model NJD-4125
IBM P/N 84G6245
FRU P/N 84G6246
EC NO. D60734
Nagano Japan Radio Co. Ltd.
Made in China

Input

100 - 125 V ~ 1.8 A
200 - 240 V ~ 0.9 A
(manual voltage switch)
50/60 Hz

Output

+3.3 V @ 4.5 A
+5 V @ 11.5 A
+5 V @ 0.02 A (stand-by?)
-5 V @ 0.2 A
+12 V @ 1.2 A
-12 V @ 0.25 A

Total 57.5 W Max. for +3.3 V and +5 V combined.

Power Supply Connectors Pinout

Planar Power Connectors P1/P2

The P1/P2 connectors use the "standard" PC AT PSU pinout.

Planar Power Connector P9

Planar Power Connector P11 - 3.3 V

Riser Power Connector P10 - 3.3 V

Power Supply Fan

The rear portion of the PSU where the fan is enclosed is taller than the rest of the unit. The fan pulls air not only through the PSU but also around the hard drive that is normally installed right above. The fan will slow down if the total system power consumption is lower than 50 W, and will stop to spinning completely if below 30 W. Thus the cooling fan usually stays idle.

Sandy's experience and fan modification (edited):
   When I got the 6860 I've immediately noticed that the fan wasn't running at all. As I didn't know about this unique feature I thought there must be some fault on the circuit board of the PSU. I disassembled PSU and soldered 12V line directly to the fan assembly. Only latter on have I learned about this unique function. The jumper wire is still there... Some machines have input AC voltage selector. Mine has a "fan mode selector", summer mode with direct connection and winter mode with original connection.

The machine works fine under DOS. But under Win95B it usually freeze at start up after the Win95 logo appears on the screen. I solved this symptom by modifying MSDOS.SYS to have a start up menu with default boot for Win95 after 60 seconds of delay time to boot. Maybe mine needs some delay for stable DC output for planar, a hard drive and a CD-ROM. I'm sure that this symptom is not related to the above mentioned fan cable modification, 'cause I have the same problem even when I switch back to the original cable connection.