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HP8563 show sidebands on CW and high noise level

Question asked by sm7ovk on Feb 6, 2020
Latest reply on Apr 7, 2020 by noiseguy

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Haven't been very active for some time. When I now started my old HP-8563E it shows two faults;

1. when I connect any CW-signal I get sidebands about 400-450kHz on each side of the carrier. These are shown about 53dB below the carrier and are on all CW-signals. (Not when I look with another analyzer.)

2. Noise level seems very high. I get a broad band of noise with the analyzer after reset and there isn't any dark part of the screen below the "noise band".

No errors recoreded.

Any ideas?

Regards 73 Jens, SM7OVK

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sm7ovk Feb 8, 2020 5:47 AM
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I assume that the 400kHz originates from the power supply, so probably some electrolytic capacitors have to be changed. When I check with a small probe there is a lot of 400kHz in the power supply.
This is a picture with the increased noise level. Compare with the normal displayed noise below. The displayed "band" of noise is about 2 squares in the normal but all the way down in the faulty. Any ideas what this could be?

Regards Jens
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noiseguy Apr 7, 2020 5:35 PM
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Several possibilities. I see error 906 on the screen, plus you have noise across all bands indicating that whatever the issue is, it is common to both, the low band and the microwave band, possibly to the time base itself. (If other errors are present, other possibilities exist as well.) Areas of influence would be: LO level or FM, A15 IF converter/amplifier issues, Log amp or BW card issues, and possibly power supply. To isolate, try to measure the LO out on the front panel, observing on another spectrum analyzer. It should read approximately 14.5 dBm and look clean (no sideband noise). Second, check your time base out on the rear panel. It should be > 0dBm and also clean. Third, if you inject a CW signal of 10.7 MHz into the IF in on the front panel at -30 dBm, tune to any frequency in the low band, < 2.9 GHz) you should get a straight line across the top of the screen. If any of these fail, LO? bad YIG, distribution amp, or driver; Time base? A15 or time base oscillator bad or came disconnected; IF gain failure? A15 IF amp or path bad or problem prior to the third IF, A15; Power supply. There are other things you can try, but requires opening the unit and this can be disastrous if you do not close it up properly post trouble shooting. If you do venture inside, check that all cables are still intact, especially on the A15. If you have the ability to check signals, you can look at the IF signals, 10 MHz distribution ports, and try disconnecting the number 7 wire (violet) and see if your noise level drops, to determine where the problem originates, in the IF section, or prior in the RF section. Highly recommend getting a service guide if possible. If you are not comfortable doing any of the above, I recommend sending to Keysight for repair. I cannot over express caution in the closing of the instrument. Cables can be pinched or damaged very easily. If it feels like you have to force it closed, stop and look where the friction comes from. Cables can be pinched in the hinges, in the back corners, not laid correctly under the "leafs", (boards). There is no room for error.
Hope this helps.
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HP8563 show sidebands on CW and high noise level

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