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Hi all,

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I recently acquired another 8753D unit for parts. It turned out that the YTO is completely dead.

I've followed the source check flow chart including verifying the YO Coil Drive waveforms with Analog Bus and oscilloscope.

I've also hooked up the 5086-7934 module directly to 5V, 15V and coil current, no output at all. The 3.8GHz LO works as expected.

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After finding lots of useful info, mainly in this groups archive I see the following repair options:

So let's evaluate the options:

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Comments about the options? Or any other suggestions?

I'm leaning to start trying option 3 or maybe option 4.

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Best regards

Marcus, SA5PMG

Hi again,

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found some very interesting info for option 3:

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Br

Marcus

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Yeah, mine is also dead for about a year now. My plan is also to build a substitute one by another YIG. Haven't made any progress yet...too much other work. If you have some progress done, please report it here ;)

Indeed, my 8753D has it's second YIG installed which has gone North, and it was an expensive endeavor to fix it the first time since I went with your option 2, and now that one has failed a mere 4 years later.? It started giving fits in just certain sections of the 6GHz band, and now there's no reference detected anywhere.
Due to the same constraints as LeonP, I also have not worked on this yet.??
Please do let us all know what you come up with, as I'm now working under the assumption that there's two types of 8753x YIG oscillators:? Those which have failed and those which will soon fail.? It seems to be the bane of an otherwise excellent and still mostly relevant VNA.

Hi all,

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I'm happy to report that I've successfully running the Wiltron YTO in my HP8753D :-)

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All thanks to well documented YTO replacements for the HP8753C and the luck that HP8753D have almost identical A11 Loop filter and EYO driver.

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To get the YIG working I had to utilize the -15V line in pin1 on the EYO connector in the A3 source to make -5V for the Wiltron YTO.

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I did not change the A11 Q7 transistor, but I put a 2mm thick copper plate under it.

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And do not forget to run all the adjustments that is necessary after A3 source module change.

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Before and after pics below.

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Any questions, just post in this thread and I'll try to answer.

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Best regards

Marcus, SA5PMG

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That is good news Marcus! You have inspired me to tackle the job myself.?

73,

Matt, KD4PBS

Marcus-

Fascinating and wonderful solution.? I still have a few questions for you or anyone else who cares to answer.? Please forgive my ignorance:

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1)? The YIG listed on your original link is an Avantek ASF-8347M.? The picture shows something that is 4-8 GHz.? First of all, what do all of those part numbers mean?? I was looking on ebay and I'm seeing a fair number of Avantek YIGs that are 4-8 GHz, but they have numbers like S09-1358 or SF6-0997M.? So my questions:

? a)? Do you need to start with an ASF-8347M, or do the other 4-8 GHz models work in the same way?

? b)? The VNA goes from basically 0-6 GHz.? Why does the YIG go from 4-8 GHz?

? c)? Could one use a YIG with a larger range, such as 2-8 GHz instead?? Would the cal proceedure adjust the instrument so that it just didn't use part of the range?? For instance, S080-0686 or Y084-1215 seem to be available.? Are there drawbacks to this approach, such as reduced frequency stability?

? d)? The origional HP part appears to be 5086-7834 and appears to go from 3.8-7 GHz.? From this perspective the 4-8 GHz replacement kind of makes sense, but does the lack of ability to function at 3.8 give you any issues?

? e)? Are the first two digits of the part the production year?? I'm seeing a lot of 080, 83, 84, etc., in these numbers which looks to me like parts coming from the early 1980s.

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Very cool that there are people here smarter than me who have figured out how to make this work.? I looks like the original replacement parts (5086-7834) run around $800 USD, whereas these replacements are sometimes sub $100.

Hi Scott,

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I'll try answer your questions.

Let me first explain the differences between HP8753B & C and newer versions such as D/E/ES/ET.

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B&C achieves its RF output by mixing a fixed YIG oscillator at 3.8GHz and a YIG Tune Oscillator sweeping between 3.8-6.8GHz. This gives a range of 0-3GHz. The 6GHz option on the B & C versions are done by a frequency doubler.

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D and newer versions also uses a 3.8GHz YIG oscillator and without the 6 GHz option the YTO sweeps between 3.8-6.8GHz just as the B&C versions. But the D/E/ES/ET 6 GHz does not utilize a frequency double, instead it uses the YTO directly without mixing, i.e. the 6GHz option requires the YTO to be able to sweep between 3-6.8GHz.

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For more details regarding this I recommend reading the "theory of operation chapters" in the service manuals for respective model.

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Simon's excellent documentation refers to HP8753C, I have repaired a HP8753D so the YTO requirements differs.

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1) I have not tried to decode YIG part numbers, some manufacturers have frequency range in the model number, some don't, some does but only on certain model series.

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a) To repair a B or C version you might get away with a 4-8GHz YTO, if it manages to have enough output power at 3.8GHz. I would certainly take my chances on this. But probably not for a 8753D/E/ES/ET 6GHz replacement which requires enough output power at 3GHz. I guess some 4-8GHz YTO won't even oscillate at 3GHz.

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My experience is that many YTO works in a similar way with their current consumption and how they need to be controlled. For me the HP economy YTOs are the exception with not requiring negative voltage and only consume less than half the main coil current.

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b) See above.

c) probably, the Wiltron YTO I used tunes over 2.5GHz-8GHz. The thing is to make the A11 controller give the correct amount of current for the desired frequency.

d) See above

e) No idea

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I would not buy a original replacement unless it was guaranteed that is has been refurbished. Otherwise it will break sooner than later.

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Smart people: I relied heavily the work of Simon and had some help from a friend that knows electronics well, I just know enough to know when to ask for help.

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Best regards

Marcus

Greetings,

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Given the YTO weak link, I purchased an Aventek ASF-8347 off eBay as an insurance policy for my 8753D opt-11.

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a) To repair a B or C version you might get away with a 4-8GHz YTO, if it manages to have enough output power at 3.8GHz. I would certainly take my chances on this. But probably not for a 8753D/E/ES/ET 6GHz replacement which requires enough output power at 3GHz. I guess some 4-8GHz YTO won't even oscillate at 3GHz.

I wanted to confirm that it covers the required 3.8 to 6.8 GHz, it clearly does and then some.

The linearity is quite remarkable:

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And plenty of power out as well:?

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Just an FYI on this particular model.?

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Best regards,

Dick Benson

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