rthomps@pacsbb.UUCP (Robert Thompson) (06/18/89)
P-BOX POWER SUPPLY BOOST The following directions will increase the output of the P-box power supply to handle 1 half height floppy and 1 LOW POWER half height hard drive. CAUTION - It is possible to damage the system and cards if this is not performed correctly! Parts list: 1 12V regulator, FAIRCHILD 7809, UA78H12CKC or equivilant 4 3 amp diodes, PIV 200 volts (RADIO SHACK) 1 1000 uf radial capacitor, at 35 volts 1 TO-3 heart sink (JDR Microdevices) sells the perfect one * SEE NOTE small amount of silicon heatsink compound Remove the P-box cover by removing the 15 or so phillips head screws and sliding the cover forward. Remove the power supply board (the only printed circuit board in there) and disconnect the wire connectors by pushing the tabs through the board and pivoting them away. You will see the regulator in the middle of the board. Carefully unsolder the 2 connectors on the back, and use solder wick or a suction device to remove the melted solder. DO NOT force it, but gently lift it away as you reheat each connector pin to soften any remaining solder. Apply silicon heatsink compound to the back of the new regulator and heat sink and install them in the same place. Be careful to apply very little solder to avoid making a solder bridge underneath the regulator. Immediately next to one end of the regulator, you will see a small black 47 uf capicitor. Cut the leads of the 1000 uf capacitor to a reasonable length, and solder the + lead to the + lead of the small black capicitor, and the - lead to the - lead of the small black capacitor. This will give a boost to the drive motor to help get the disk turning when a drive is selected. Now for the hard part. The 4 diodes must be installed in place of 4 smaller diodes on one corner of the card. You will see 8 small tubular devices in a row on one corner of the card. Four of these (the dark colored ones with a colored stripe or band on one end) are the diodes. The other four (lighter colored) must not be disturbed. Carefully note which direction the bands point (my board had markings on it to indicate direction, but all boards may not have them), and then remove the diodes. Use the same methods used to remove the regulator. Now you must slightly enlarge the holes to match the wire size of the new diodes. Use a small drill of just slightly larger size than the wire to do this. Use a pin vise, or some other holding device to do this by hand. DO NOT attempt to use a mechanical or electric drill to do this. Watch the trace on the board carefully while drilling to be sure that you are not ripping it off the board! Cut the wires on the new diodes to about 3/8 inch length, and insert them carefully into the holes. You may need to bend some of them slightly to get a good fit. After they are all inserted, CAREFULLY solder the ends, being VERY careful not to connect ends that were not previously connected by the traces on the board! Now carefully reinstall the board and the connectors, and before installing the cover of the P-box, turn it on. Quickly check for 12V across the 1000 uf capacitor leads. If all is ok, reassemble the P-box, taking care not to pinch the drive wires along the back of the box. (*) If you use the drives normally, this is sufficient. Make sure you have GOOD ventilation in the power supply area. Increasing the 110 volt fan to one with a greater CFM output could be helpful! You should also drill at least 25 1/4 inch holes in the floor of the drive section and a least 25 1/4 inch holes in the REAR panel of the drive section to allow for heat dissapation from that area via convection!