43
Table 3-12. Secondary Interface S.A. Test No. 5
Description
: These signatures check the chip select IC U304 and the status readback IC U303. The signatures are valid for
U301 firmware revisions "Rev A.02.01". Use the test setup described in the ''Test Setup for S.A.".
Signatures:
+5V U303-16 U304-6,16
Common U303-8 U304-5-8
SD(0) U303-10 = UFOA S0 U304-1 = 24A7
SD(1) U303-13 = AP48 S1 U304-2 = A264
SD(2) U303-9 = U93A S2 U304-3 = OUPA
SD(3) U303-1 = P070
CS0 U304-15 = 57A2
LCLR U303-4,6,12,14 = P921 CS1 U304-14 = 1UPU
UNREG U303-11 = H82C CS2 U304-13 = CCF9
BO U303-3 = H82C CS3 U304-12 = P9HA
OV U303-7 = H82C CS4 U304-11 = 4OH3
OP U303-15 = H82C CS5 U304-10 = 9457
STAT_EN U303-5 = HH1A RCK_LOW U304-9 = UP15
RCK_HI U304-7 = 355F
STB U304-4 = HHC8
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 S.A. mode by connecting the jumpers in test headers
TP201 and TP301 in the S.A. mode positions (see Figure 3-2). The waveforms shown in Figure 3-3 can only be generated
when the S.A. mode is on.
First, check that the S.A. waveforms shown on Figure 3-3 are correct. If these waveforms are not correct, check the SD0-7
data bus lines to the readback DAC U322 using S.A. Tables 3-10 and 3-13. Next, check the SDB0-7 data lines to the main
(U320) and transient (U321) DACs using S.A. Table 3-9. If there is a problem on the data lines, S.A. should isolate the
problem to the faulty component.
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