Service manual

100 Replaces page 39
Table 3-14. Chip Select, Status Readback, EEPROM Decoder Signature Analysis (Secondary)
Description
: These signatures check the chip select IC U304, the status readback IC U303, and EEROM decoder U341 The
signatures are valid for U301 firmware revisions "Rev A.01.01" and "Rev A.01.02". Use the test setup described in the
''Test Setup for SA".
Signatures:
+5V U303-16 = 1CAU U304-6,16 = 1CAU U341-20 = 1CAU
Common U303-8 U304-5-8 U341-10,13,15,17
SD(0) U303-10 = 1P45 S0 U304-1 = CH72
SD(1) U303-13 = 2OOF S1 U304-2 = 6471
SD(2) U303-9 = 89AA S2 U304-3 = 21A2
SD(3) U303-1 = 93AU
CS0 U304-15 = 21PA
LCLR U303-4,6,12,14 = 8933 CS1 U304-14 = 868PA
X U303-3 = 1CAU pulsing CS2 U304-13 = H53P
UNREG U303-11 = unstable CS3 U304-12 = UFP7
OV U303-7 = 1CAU +5V CS4 U304-11 = P8OC
OP U303-15 = 1CAU+5V CS5 U304-10 = P27H
STAT_EN U303-5 = P6C3 RCK_LOW U304-9 = 6746
RCK_HI U304-7 = 48U7
STB U304-4 = COH6
SD(0) U341-2 = lP45 U341-1 = 1CAU +5V
SD(1) U341-4 = 200F U341-11 = 1CAU +5V
SD(2) U341-6 =89AA U341-12 = 1CAU +5V
SD(3) U341-8 =93AU U341-14 = OOOO
SD(4) U341-9 = 7792 U341-16 = 1CAU +5V
SD(5) U341-7 = O343 U341-18 = 1CAU + 5V
SD(6) U341-5 = FPOU U341-19 = 1CAU +5V
SD(7) U341-3 = 6740
DAC Circuits Troubleshooting (Figure 3-3)
These circuits generate the SLEW signal which controls the input power stages. This analog signal is produced by the
combined outputs from the main DAC/amplifier (U320/U326)and the transient DAC/amplifier (U321/U325). The
DACs/amplifiers convert the data on bus lines SDB0-7 into analog signals.
The
HIGH signal (active LO) from the transient generator (see Figure 3-7) closes switch U309 causing the output of the
transient/DAC amplifier to be combined with the output from the main DAC/amplifier. The resulting SLEW signal is sent
to the input power control circuit via inverting amplifier U324 and the slew circuits (see Figure 3-4).
The SLEW signal is also read back to microprocessor U301 via comparator U327. Readback DAC/amplifier U322/U328
converts the data on bus lines SD0-7 into a reference signal that allows the microprocessor to successively approximate the
value of the SLEW signal. The SLEW readback signal is used during selftest to determine if the DACs are operating
properly.
To troubleshoot the DAC circuits, place the Electronic Load in the SA mode by connecting the jumpers in test headers
TP201 and TP301 in the SA mode positions (see Figure 3-2). The waveforms shown in Figure 3-3 can only be generated
when the SA mode is on.