Troubleshooting
2-115
Test 412.1 – AC amps switch
Pass/Fail
Cannot measure 1.7V ±0.3V at A/D IN.
The 9.2mA ohms source is turned on to dump current through switch U323 (ACAL
pulled low) to the amps protection diodes (CR305 and CR309). The three diode voltage
drop is routed through U317 (/200uA pulled low), U320 (/ACA pulled low), U510
(REL3 pulled low), U526 and Q516 to the input buffer (Q512 and U520). The buffered
signal is tied to AMP IN.
The signal at AMP IN is then routed to the variable gain ampliÞer (VGA) and, being
positive, follows the non-inverting x1 path that consists of R530, Q509, Q507, U519,
R531, U509, Q501, and U516 to pin 12 of multiplexer U511.
The output (OUT) of the multiplexer is routed through buffer U342 to ACV/A. The sig-
nal at ACV/A is routed through U320 (/AC pulled low) and applied to the A/D buffer
(U322), which is conÞgured for x1 gain. Measure 1.7V at A/D IN.
DC_STB
Registers
R1_STB
Registers
R2_STB
Registers
U801 Q1: 0
Q2: 1
Q3: 1
Q4: 1
Q5: 1
Q6: 0
Q7: 0
Q8: 0
U307 Q1: 0
Q2: 0
Q3: 1
Q4: 1
Q5: 1
Q6: 0
Q7: 1
Q8: 1
U505 Q1: 1
Q2: 1
Q3: 1
Q4: 1
Q5: 0
Q6: 0
Q7: 0
Q8: 0
U800 Q1: 1
Q2: 1
Q3: 0
Q4: 0
Q5: 0
Q6: 0
Q7: 1
Q8: 1
U305 Q1: 1
Q2: 0
Q3: 1
Q4: 0
Q5: 1
Q6: 1
Q7: 1
Q8: 1
U500 Q1: 1
Q2: 1
Q3: 0
Q4: 1
Q5: 1
Q6: 0
Q7: 0
Q8: 1
U300 Q1: 1
Q2: 1
Q3: 1
Q4: 1
Q5: 1
Q6: 1
Q7: 1
Q8: 1
U302 Q1: 0
Q2: 0
Q3: 0
Q4: 1
Q5: 1
Q6: 1
Q7: 1
Q8: 0
U530 Q1: 1
Q2: 0
Q3: 0
Q4: 0
Q5: 0
Q6: 0
Q7: 0
Q8: 0
U303 Q1: 0
Q2: 1
Q3: 1
Q4: 1
Q5: 0
Q6: 1
Q7: X
Q8: X
U501 Q1: 0
Q2: 0
Q3: 1
Q4: 1
Q5: 1
Q6: 1
Q7: X
Q8: X
Note: Tables 2-10 through 2-12 provide functional descriptions of the register bits.
Type
Failure analysis
Description
Bit pattern
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