A digital control problem will cause the following three steps to fail.
1.On the HP 8560A, press
2.A click should be heard after pressing dB in step 1, unless ATTEN was previously set to 70 dB.
3.Press 0, @, and @. Another click should be heard. If no clicks were heard, but the ATTEN value displayed on the CRT changed, the digital control signals are not operating properly.
Analog Bus Drivers
See function block N of A3 Interface Assembly Schematic Diagram (sheet 4 of 6).
1.Press cm) on the HP 8560A, and set the controls as follows:
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz TRIGGER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single
2.Monitor A3U401 pin 3 (LRF_STB) with an oscilloscope or logic probe. This is the strobe for the Al5 RF assembly.
3.Press (mCTRL) INTERNAL MIXER and check that pulses occur when toggling between SIG ID ON and SIG ID OFF.
4.Monitor U401 pin 5 (LFC_STB) with an oscilloscope or logic probe. This is the strobe for the Al4 Frequency Control assembly.
5.Press (AMPLITUDE) and check that pulses occur when toggling between ATTEN settings of 10 and 20 dB.
6.Monitor U401 pin 7 (LIF_STB) with an oscilloscope or logic probe. This is the strobe for the A5 IF assembly.
7.Press (AMPLITUDE) and check that pulses occur when toggling between REF LVL settings of
8.Monitor U401 pin 9 (LLOG_STB) with an oscilloscope or logic probe. This is the strobe for the A4 Log Amplifier/Cal Oscillator assembly.
9.Press
LOG dB/DIV .
10.To check the Address and Data Lines, place a jumper from A3TPl and A3TP2 to A3U406 pin 20 (+5 V).
11.Check that address lines A0 through A7 and data lines DO through D7 are all TTL high.
12.If any address or data line is low, set the LINE switch off and disconnect the W2 control cable from A3J2. Set the LINE switch on. Ignore any error messages.
13.Check that address lines A0 through A7 and data lines DO through D7 are all high. If all address and data lines are high, suspect a fault either in W2 or one of the other four assemblies which connect to W2.