TM 11-6625-2958-14&P

 

 

Table 5-7. Preregulator Troubleshooting (Continued)

 

 

 

 

 

 

 

 

 

 

 

STEP

 

ACTION

 

RESPONSE

 

 

PROBABLE CAUSE

 

 

 

 

 

 

 

 

 

 

2

Connect

oscilloscope be-

a.

Normal

waveform.

 

a.

Defective

T70.

 

tween TP85 (+) and TP103

b. Little or

no

voltage.

 

b. Defective

Q72, Q73,

 

(-).

 

 

 

 

 

 

 

 

 

 

CR76, or C71. pro-

 

 

 

 

 

 

 

 

 

 

1

 

I

 

 

 

 

 

ceed to Step 3.

 

 

 

 

 

 

 

 

 

 

 

 

Amplitude

incorrect.

 

a.

 

 

 

Connect

oscilloscope be-

a.

 

Defective

Q71, C70,

3

tween TP80 (+) and TP103

 

 

 

 

 

 

C72, CR74, CR75,

 

 

 

 

 

 

 

 

 

 

 

(-).

 

 

 

 

 

 

 

R82, R75, or R78.

 

 

 

 

 

 

 

 

 

 

 

b. Period

incorrect.

 

b. CR78 defective. Pro-

 

 

 

 

 

 

 

 

 

ceed to Step 4.

 

 

 

 

 

 

 

 

 

Connect

oscilloscope be-

a. Amplitude, dc reference or

 

a.

Defective

CR82,

4

tween TP82 (+) and TP103

 

period

incorrect.

 

 

CR84, CR79, CR80,

 

( - ) .

 

 

 

 

 

 

 

CR77, CR78. Check

 

 

 

 

 

 

 

 

 

R87.

 

 

 

 

 

 

 

 

5

Connect

oscilloscope be-

a. Amplitude, dc reference or

 

a.

Defective CR81,

 

tween TP81 (+) and TP103

 

period

incorrect.

 

 

CR83, R86, R83,

 

(-) .

 

 

 

 

 

 

 

C73.

 

 

 

 

 

 

 

 

 

 

 

 

5-62DISASSEMBLY PROCEDURES

5-63 The following seven paragraphs describe procedures for removing and disassembling the five subassemblies in this supply (A1 main circuit board, A2 RFI assembly, A3 interconnection circuit board, A4 heat sink, and A5 front panel). These procedures are referenced throughout the manual wherever necessary. For example, in the instructions for converting the supply to 115Vac opera- tion, reference is made to the RFI assembly removal procedure in order to allow access to the bias transformer (A3T2) primary connections.

5-64Main C ircult Board (Al) Removal. To remove the main printed circuit board, proceed as follows:

a. Unplug unit and remove top cover of supply.

b.Remove six hold-down screws visible on component side of main circuit board (arrowed “A” through “F” in Figure 7-1 O).

c.Unplug board from receptacle mounted on interconnection circuit board by gently pulling on finger hole in opposite end of circuit board. Only finger hole should be used to remove board; do not pull on beard-mounted components to aid re- moval. Care must be taken that rear barrier strip clears opening in rear panel.

5-65Front Panel (A5) Removal. To remove the front panel, proceed as follows:

a. Unplug unit, turn supply upside down, and remove four screws holding handlers to front panel.

b. Front panel may now be swung outward, hinging on wires to LINE circuit breaker. Access is provided to all panel-mounted components.

5-66 Main Filter Capacitor Bank Removal. To remove the main filter capacitors (Cl 01 through

C104),

proceed

as follows:

a. Unplug

unit, remove top and bottom cov-

ers of

supply.

,

 

b.Remove one long screw and hold-down bracket on top of supply (arrowed “A” in Figure 7-3),and one long screw and hold-down bracket on bottom of supply (arrowed “A” in Figure 7-4).

c.Sufficient lead length is provided to al- low capacitors to be lifted partially out of instru- ment.

5-67 RFI Assembly (A2) Removal. To remove the RFI assembly, proceed as follows:

a. Unplug unit, turn supply upside down, and remove bottom cover.

b. Remove four screws holding RFI heat sink to mounting brackets (arrowed “A” through “D” in Figure 7-5). Two of the screws are accessible through holes in chassis flanges.

C. Lift out RFI assembly and turn over.

d. Remove four screws holding cover to heat sink (screw holes are arrowed “A” through “ D“ in Figure 7-1). This allows access to A2R1, A2C1, and A2L1A/A2L1B with its jumpers for 115/230 volt operation.

. Remove four screws holding A2L1A/A2LlB mounting bracket to heat sink. (Two of the screws

5-15