to-3000
Joined: 05 Aug 2007
Posts: 1
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 Posted:
Mon Aug 06, 2007 1:35 am Post subject:
8568a spectrum analyzer yto unlock and more... |
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Hello all,
I am trying to debug an odd problem with an HP 8568A spectrum analyzer. One day after maybe being on for ten minutes, YTO unlock appeared on the screen. Then, there was no more sweep, just a bold green flat line on the bottom of the screen (along with the normal screen stuff, like the grid and frequency span info).
When I start troubleshooting the thing, I hit INST PRESET as the diagnostics are to be made in this mode, and I discover that the waveforms for the YTO tune DAC output and the Sweep Attenuator output are jittery and their voltages not according what was indicated on the schematic.
So anyway, I turn the thing off and unplug it, and just out of curiosity I open the processor+memory housing where those boards are located and decide to pull the memory board out just to look at it. Neat. Can't believe they did all those tracks with the old drawing and magnifying lens method. Sheesh! You can layout a board like that using autoroute in in a few minutes today! But that's beside the point. I put the board back in, close the cover for that section, and fire up the analyzer. Well to my surprise, I couldn't get my jittery signals back. They're gone! I got no sweep signals, much less a darn YTO unlock error. I thought, maybe the 10.285V reference voltage is gone but no, it's still there. I am totally in the ditch now... ARGH!
2:15AM, time to get some sleep.
The next day, I plug the display unit in, which I had not connected to the RF section. I turn on the analyzer, and as "luck" would have it, there's the YTO unlock, there's OVEN COLD (that's good at least it knows it's been off for over 12 hours) and the commands still work, there's no more inst alarm leds on (the left LED used to be on all the time). This is getting weird. And that's not all. After ten minutes,
NO MORE YTO UNLOCK message!
How about that? Didn't fix any of the problems, I still don't have a sweep, not even the 100kHz sideband from the internal oscillator difference.
No SWEEP.
Anybody got any idea?
Now I'm aiming my SOS to those techs out there who have fixed these things when they were used everywhere, because I know you've probably seen this before.
Thank you for any help you can provide,
Owen
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The simplicity if OLD TECH is what makes good, dependable, easily serviceable and understandable! |
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