Hi,

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Looking at this trace on the graph, what catches my attention is the fact that the control voltage applied to the YTO makes jumps at the start and end of the YTO range, and is linear in places, but mostly the fact that part is curved.

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Maybe the YTO driver is more complex than I imagine. Perhaps there is switching in the transconductance amp powering the YIG coils, and one or more of these circuit sections are distorting...hard to say.

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I saw a friend of mine yesterday, and he had three 8133As available to do some quick testing. On 2 of these generators tested, there was a relay problem, one was on the CH2, normal output, and the other was on the reversed output. Their problems were exactly the same as on my 8133A which I ended up repairing. No doubt this problem is recurring on these generators.

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I measured the FM modulation at Spectrum at 500 MHz on these two generators, and I had the same result as on mine...this would seem normal behavior.

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I had the opportunity to use a CS803C and SD-22, and it was possible to watch the signal in PRBS mode. However, in the trigger menu it was necessary to use the EXTERNAL DIRECT trig, to switch from VARIABLE PERSISTENCE mode.

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For the CH2 relay, if the repair fails, this part is available on eBay.

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Thanks Yves,

Collecting data for frequency accuracy analysis is lengthy task. I wrote a powershell script to set frequency, read 8133A internal frequency counter reading (and the external frequency counter connected to the ch1 output.
I stepped frequency 1Mhz from 34Mhz to 3.5Ghz. The plot below shows the frequency error (set-reading from 8133A internal counter). Indeed there is some frequency issue in some bands, which does not have explanation.


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Regarding ch2 relay issue, I plan to open my unit tomorrow and try to fixt it. Let's see how it goes. Thanks for your step by step instruciton.

Thanks!

Hi,

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For the relay problem:

- I decided to try the disassembly again and it worked correctly this time.

- step#1: remove the cover, there are two screws, one of which is hidden under the label.

- step #2: you have to dismantle the relay coil to go further and it is difficult.

- step#3: I had no choice but to cut the screw head, drill and remove the debris from the screw. The replacement screw was a 2-56.

- step #4 and #5, shows the RF base including the mechanics of the relay without the activation coil.

- step #6: dismantling the external mechanics of the relay.

- step #7: separation of the RF and mechanical part of the relay. At this point the goal was to clean the gold-plated blades and contacts and reassemble that part. Reassembly was quite difficult because it requires precision. After this step was done, I tested with the VNA and when I manually pushed on the blade above the spring that we see in steps #8 and #9, everything was going well with the VNA.

- After step #7, I redid the assembly without the cover and tested everything to realize that it was not yet working correctly.

- I ended up understanding that the problem was the distance between the blade pushing on the spring base which didn't have enough pressure. So I did the disassembly in step #6, I adjusted the thin blade attached to a metal part, so that the blade barely touches the base of the spring as shown in step #9... and this solved the problem.

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So, here is my advice: do steps 1,2 and 3 and look at the blade shown in 8 and 9. If it does not touch the base of the spring, do step 6, adjust the blade to get a result like step 9 and reassemble everything without the cover and do a test on your workbench. The relay operates at +15V (97mA), pay attention to polarity. The test can be done with an oscilloscope, if you do not have a VNA or Spectrum. Choose a low frequency for the test first, for example 50 MHz, you will quickly see if the signal passes when the relay is activated. If unfortunately, the relay still has the same erratic behavior, then you will have to go further and do step 7...and that is not easy at all.

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I did the same test as you to compare, and it's difficult to explain this behavior.

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I also did this automated performance test, which is the error of the output frequency vs the programming of that frequency.

The acceptance limit is ±0.5%, but typically the error should be close to ±0.1%. This test checked all programmable frequencies from 31.3MHz to 3.5GHz in steps of 100kHz, therefore 34688 frequencies, so this test lasted several hours. The error result also includes that of thermal drift during the test.

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Tomorrow I'm going to go see a friend to do a comparative test regarding frequency stability on another 8133A.

I will probably have the opportunity to do a test on a Tektronix 11801B with SD-26 and I will check the trigger mode with a signal from the 8133A. I will give you my comments if this test can ever be done.

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Yeah,

I did ran the command and I get following, so It seems calibration is OK (it is linear)

:DIAG:CAL:YIG?
+2.02000E+09,+9.55000E+02,+2.56030E+09,+1.54500E+03,+3.02723E+09,+2.05600E+03,+3.49605E+09,+2.56700E+03,+3.95992E+09,+3.07200E+03

I re measured and plotted the set frequency and the output frequency on ch1 (using frequency counter). I see below plot. Yellow trace is the YIG frequency from 2 to 4Ghz (expected) and the blue trace is the actual frequency output, x axis is the set frequency. I measured manually from 33 Mhz to 500Mhz. Its clear that the output frequency has some issues and not linear with set frequency.


I still do not understand how 12 bit DAC translates to the YIG output, May be some bit of DAC is an issue?.

By the way, My timing board was coming from Israel, and due to what's going on over there, it is not certain if I will get it or not.?

If you end up fixing RF relay, then I will follow your pursuit and fix mine also. :)

Thanks alot.