TM 11-6625-3145-14
Maintenance: Troubleshooting-318/338 Service
12.
THRESHOLD TEST
Program: THRSH
Function:
Power on - Threshold V1 and Threshold V2 are set for several levels to produce Threshold V3 at - 0.2V or +0.2V. For
every setting the comparator will detect the Threshold V3 level relative to ground and the MPU checks the comparator’s
output against the expected data (0 or 1).
Troubleshooting - Threshold V1 and Threshold V2 are programmed from -10.0V to +10.0V incrementally with 0.1V steps
in order to generate the saw-tooth waveform.
Description: Refer to Figure 7-11. Two levels of voltage, one for V1 and the other for V2, are produced by DAC U070
and U080 (CMOS 8-bit buffered multiplexing DAC, AD7524) on the A05 ROM/Threshold board. When the MPU writes
data into these DACs, this setting is latched inside. The data is supplied from U216 (octal bus transceiver with 3-state
output, 74LS245) on the A06 MPU/Display board through the A08 Mother board, and U045 (74LS245) on the A05 board.
When the MPU writes at I/O address E0
hex
the WR and CS signals are sent to U070 (DAC V1) to latch the data. WR and
CS for U080 (DAC V2) are caused by the MPU’s access at I/O address E1
hex
. The WR signal is delivered from U150C
(quadruple 2-input positive NOR gate, 74LS02) on the A05 board, which comes from U214 (octal buffer/line driver with 3-
state output, 74LS240) on the A06 board. CS for these DACs are generated by U092B (dual 2-line to 4-line
decoder/demultiplexer, 74LS139) on the A05 board.
A number less than 80
hex
programs the DAC for positive output, and a number more than 80
hex
progarms it for negative
output centered on GND (80
hex
) in 0.1V steps. The actual output of these DACs is 1/4 of that specified in the
THRESHOLD menu.
The settings and expected data are as follows;
7-26
Summary of Contents for 318
Page 119: ...318 VERIFICATION AND ADJUSTMENT PROCEDURES ...
Page 182: ...338 VERIFICATION AND ADJUSTMENT PROCEDURES ...
Page 253: ...318 ___________________ TROUBLESHOOTING TREES ...
Page 344: ...338 TROUBLESHOOTING TREES ...
Page 517: ...TM 11 6625 3145 14 318 338 4434 923 318 Block Diagram ...
Page 518: ...TM 11 6625 3145 14 318 338 4434 924 338 Block Diagram ...
Page 519: ...TM 11 6625 3145 14 318 338 4434 925 318 Acquisition Module Wiring Diagram ...
Page 520: ...TM 11 6625 3145 14 318 338 4434 926 318 338 Mainframe Wiring Diagram ...
Page 521: ...TM 11 6625 3145 14 318 338 4434 926 338 Acquisition Module Wiring Diagram ...
Page 522: ...TM 11 6625 3145 14 318 338 4434 928 Figure 9 1 318 A01 Input A Board Component Locations ...
Page 526: ...TM 11 6625 3145 14 ...
Page 528: ...TM 11 6625 3145 14 Figure 9 3 318 338 A03 ACQ Control Board Component Locations ...
Page 532: ...TM 11 6625 3145 14 ...
Page 536: ...TM 11 6625 3145 14 ...
Page 538: ...TM 11 6625 3145 14 ...
Page 539: ...TM 11 6625 3145 14 ...
Page 540: ...TM 11 6625 3145 14 ...
Page 541: ...TM 11 6625 3145 14 ...
Page 542: ...TM 11 6625 3145 14 Figure 9 8 318 338 A10 CRT Board Component Locations ...
Page 544: ...TM 11 6625 3145 14 Figure 9 9 318 338 A11 Inverter Board component Locations ...
Page 546: ...TM 11 6625 3145 14 Figure 9 10 318 338 A12 Regulator Board Component Locations ...
Page 551: ...TM 11 6625 3145 14 Figure 9 12 338 A01 Input A Board Component Locations ...
Page 553: ...TM 11 6625 3145 14 318 338 SERVICE ...
Page 554: ......
Page 555: ...PIN 058584 ...