I am servicing my 8594E /010 analyzer. It failed at power-up. Was working fine, then suddenly failed.
Have LO UNLVL and FREQ UNCAL warning all the time. Ran diagnostics. All PASS except FM COIL DRIVE (page 243). Ramp does not show - just flat line. Value changes above 10 MHz SPAN. Here is what I understand so far:
a) this is a 1st LO failure, which is a YTO.
b) A7 card should generate a tuning ramp - does not work.
c) Page 243 of service manual suggests running unlocked by disconnecting A25 counterlock assy. Did not correct so A25 is good.
So, I guess A7 card could be bad, or YTO could be bad. Or LODA could be bad, and A7 is getting no signal to discriminate?
Would appreciate advice on how to sleuth-out problem. I do have another 8594E I can borrow to look at signals - maybe even swap-out A7 card which is pretty easy. Removing RF section seems hard.
Jeff
Have LO UNLVL and FREQ UNCAL warning all the time. Ran diagnostics. All PASS except FM COIL DRIVE (page 243). Ramp does not show - just flat line. Value changes above 10 MHz SPAN. Here is what I understand so far:
a) this is a 1st LO failure, which is a YTO.
b) A7 card should generate a tuning ramp - does not work.
c) Page 243 of service manual suggests running unlocked by disconnecting A25 counterlock assy. Did not correct so A25 is good.
So, I guess A7 card could be bad, or YTO could be bad. Or LODA could be bad, and A7 is getting no signal to discriminate?
Would appreciate advice on how to sleuth-out problem. I do have another 8594E I can borrow to look at signals - maybe even swap-out A7 card which is pretty easy. Removing RF section seems hard.
Jeff
The sweep ramp generation does come from the A7, Analog Board. The sweep ramp is routed to three different paths. Two paths depend on the analyzer span and the last path depends on the center frequency of the analyzer. One path is for analyzer spans >10 MHz, which route the sweep ramp through the Main Coil circuitry before driving the 1st L.O. or YIG oscillator’s main coil. The second path is for analyzer spans ≤ 10 MHz, which route the sweep ramp through the FM Coil circuitry before driving the 1st L.O.’s FM coil. The third path is irrelevant for your failure, but it drives the YIG Tuned Filter for the high band path, basically for input signals >~2.8 GHz.
When you unplugged the ribbon cable that goes to the Counterlock board, did you try to perform just the Freq Cal? The start of the Freq Cal internal routine will look at the frequency of the calibrator signal and if it is off in frequency by more than what firmware has built in for the “specification”, it will not run the routine. You can bypass this initial firmware check and force the frequency cal to run by pressing “Frequency -2001 Hz, Cal, Cal Freq”. Let that routine run and see if it passes. If it does, press Cal Store, then try the Cal Amptd routine. If that passes, press cal store, then turn the 9x power off and reconnect the ribbon cable on the Counterlock board and re-run these two routines.
If the Frequency Cal does not run properly with the Counterlock board ribbon cable disconnected, my advice would be to swap the Analog Bd. since you have that luxury.
Hope this helped -