A7 Loda (Lo Distribution Amplifier) - HP 8560A Service Manual

A7 LODA (LO Distribution Amplifier)

Note
YTO unlock errors may occur if the power delivered to the A15A2 Sampler is
less than -9.5 dBm. Frequency response will be degraded in both internal and
external mixing modes if the output power is low or unlevelled.
Caution Connecting or disconnecting the A7 LODA's bias with the HP 8560A IuNE]
switch on will destroy the A7 LODA. Always set the HP 8560A (LINE switch
off before removing or reinstalling W12 to either the A7 LODA or A14JlO.
Note Error 334 may be displayed if the LO OUTPUT connector on the front panel
is not properly terminated into a 50R termination.
1. Set the HP 8560A's (LINE) switch to off. Disconnect W12 from A14JlO.
2. Connect a jumper between A14JlO pin 5 and A14J19 pin 6. Connect a jumper between
3. Connect a DVM's positive lead to A14J18 pin 14 and the negative lead to A14J18 pin 6.
4. Set the HP HP 8560A's m switch to on.
5. The voltage measured on the DVM should be more negative than -9.4 Vdc.
6. Move the jumper from A14J18 pin 1 to A14J18 pin 2. The voltage measured on the DVM
should be more positive than t12.3 Vdc.
7. If the voltages do not meet the limits listed in steps 4 and 5, troubleshoot the Al4
Frequency Control assembly.
8. Connect the positive DVM lead to A14JlO pin 1.
9. The measured voltage should be approximately +5 Vdc. If the voltage is not +5 Vdc,
troubleshoot the Al4 Frequency Control Assembly.
10. Connect the DVM's positive lead to A14J18 pin 1. The voltage should measure within 5%
of the GATE BIAS voltage listed on A7 LODA's label.
11. If this voltage is not within this range, rotate A14R628 GATE BIAS through its range
while monitoring the DVM.
12. If the voltage varies between 0 Vdc and -2 Vdc, adjust A14R628 GATE BIAS for a DVM
reading within 5% of the GATE BIAS voltage listed on A7 LODA's label. If the voltage
does not vary between 0 Vdc and -2 Vdc, troubleshoot the Al4 Frequency Control
assembly.
13. Disconnect the jumper from A14J19 to A14JlO. Set the luNE] switch off. Reconnect W12
to A14JlO. Set the (LINE) switch on.
14. If the DVM reading changes significantly, the A7 LODA is probably defective.
11-6 RF Section