TM 11-6625-2958-14&P

are arrowed “E” and “F“ in Figure 7-1.) Lifting brackets away from heat sink allows access to triac A2CR1. A magnetized screwdriver is useful in performing this step.

5-68 Heat Sink (A 4) Removal. In order to gain access to the following components, it is necessary to remove the heat sink assembly. Transistors A4Q101 through A4Q108; diodes A4CR1OI through A4CR106, A4CR108, and A4CR110; resistors A4R106, A4R123, and A4R150 through A4R155; capacitors A4C1 through A4C5; cooling fan A4B1; and thermal switch A4TS101. For the location of these components, see Figures 7-5,7-6,7-7,and 7-8.To remove the heat sink assembly, proceed as fol- lows:

a.Unplug unit, stand it on left side, and remove top and bottom covers.

b.Remove main printed circuit board as described in Paragraph 5-64.

c.Remove two screws holding upper edge of heat sink to upper chassis flange (arrowed “E” and “F” in Figure 7-D).

d.Disengage two pins holding lower sec- tion of heat sink assembly to main circuit board support tray by sliding heat sink down about ½ inch and slightly away from chassis. Before fully removing heat sink assembly, observe lead dress so assembly may be returned easily to correct po- s it ion.

e.Maneuver heat sink assembly down- wards and away from chassis until it is resting on table (sufficient lead length is provided). Gentle leverage with a thin screwdriver may be necessary to allow heat sink assembly to clear upper chassis flange. Access is now provided to all components mounted on heat sink except resistors A4R150 through A4R155, and A4R123,

5-69 Heat Sink (4) Disassembly. To gain access to resistors A4R123 and A4R150 through A4R155

(shown in Figures 7-6and 7-8)it is necessary to disassemble the heat sink assembly by utilizing the following procedure:

a.Remove heat sink assembly as described in Paragraph 5-68above.

b.Turn supply upside down and place heat sink assembly partially into chassis so fan (A4B1) is protruding above chassis.

c.Remove four screws and four shoulder washers attaching fan mounting plate to heat sink. Do not remove fan from mounting plate. When re- assembling heat sink, do not overtighten these screws. Too much tension will damage the insu- lating rods.

d.Remove two screws holding current sam- pling resister A4R123 to topmost two portions of heat sink. If necessary, the resistor may be

unsoldered at this point.

e.Remove mounting nuts from A4CR106 on left side of heat sink, and from A4CR108 on right side of heat sink. Remove mounting nuts, bolts and shoulder washers on transistor A4Q102 on right side of heat sink (see Figure 7-5).

f.Slide top section of heat sink forward and off insulating rods.

9.Remove four screws holding emitter re- sistor circuit board to bottom half of heat sink. A magnetized screwdriver is useful here. Access is now provided to series regulator emitter resistors A4R150 through A4R155 (see Figure 7- 6).

h.If necessary to completely remove emit- ter resistor circuit board, unsolder connections to board, marking wires to enable correct replacement, and remove board.

5-70 Interconnection Circuit Board (A3) Removal. To replace capacitor A3C3 or transformer A3T2, (shown in Figure 7- 2), it is necessary to remove the interconnection circuit board by utilizing the following procedure:

a.Remove main circuit board, RFI assembly, and heat sink assembly as described in Paragraphs 5-64,5-67, and 5-68 respectively.

b.Remove six screws holding back panel to chassis frame.

c.Stand supply on left side, and remove two screws holding main circuit board support tray to back panel. Move panel away from frame.

d.Remove two screws holding main circuit board support tray to internal chassis divider.

e, Working from top rear of supply, inter- connection circuit board (still attached to main circuit board support tray) can be angled up enough to allow access.

f.If necessary to completely remove inter- connection circuit board, remove two screws hold- ing board to support tray, one screw holding ca- pacitor clamp (A3C3) to support tray, and two screws holding bias transformer (A3T2) to support tray. Unsolder connections to board, marking wires to enable correct replacement, and remove board.

5-71REPAIR AND REPLACEMENT

5-72 Section VI of this manual contains a list of replaceable parts. If the part to be replaced does not have a standard manufacturers’ part number, it is a “special” part and must be obtained directly from Hewlett-Packard. After replacing a semiconductor device, refer to Table 5-8for checks and adjustments that may be necessary. All components listed in Table 5-8without A-designators are on the main printed circuit board (Al).