| Electronics > Repair |
| E4433B RF sig gen repair |
| << < (9/9) |
| microbug:
Well that weekend came and went. I now have a TinySA Ultra, which I'm very pleased with. I decided to try using a freezer spray on the vector output board while in operation. I tried freezing the mixer chip and no change (still a small 2.7GHz peak). I tried freezing U80 (the RF amp after it) and the peak disappeared. Interesting. So I tried measuring at the mixer output and found the 4GHz signal I expected. The 2.7GHz signal was also there, but I think it was just coupled from somewhere else. I removed the baluns between the mixer and U80 and tested them. They are fine, at least at DC. No damage visible under magnification. I then tried measuring the input to U80 (disconnected from U80 -- straight into the spectrum analyser). What do you know, the signal I wanted! Also, U80's output is 6 Ohms to ground. That seems pretty suspicious, there aren't any external DC bias components on that pin. So I suspect U80 (which is the same part that caused the problem in the Signal Path video, although not sure if it is the same device inside the Agilent package). I think I can try bypassing it with some coax, it will be a bit of a nasty job but should prove the principle. Fingers crossed for this. There have been a lot of red herrings on this repair, some definitely because of dodgy coax connections. Others because of that 2.7GHz signal coupling everywhere. It's all a learning experience... Edit: it seems unlikely that U80 is the same MSA-0686 as on the board revision shown in the TSP video. The IC on my board has +9V and -5.3V power inputs, the MSA-0686 has a single-ended power input. |
| vaualbus:
Cool finally an update! Wow good find yeah this repair was "cursed" we always believed about the IQ modulator but at end it seems this due to the next component in the chain :-DD |O So yeah 6ohm is way too low, I guess. Those are custom Agilent parts, I think they use the same parts, as I said to you before, in different instruments of the same period. This must be a bad design from Agilent as a lot of people have trouble with this 1GG43-4205 https://groups.io/g/HP-Agilent-Keysight-equipment/topic/esg3000a_e4421a_signal/86763436?p= I am glad it is not (yet) failed in my unit I would say I think later revision boards use more off the shelf components instead of this hybrid IC. By the way U140/U180 are the same IC, so you could try remove it tested it and see if it has the same 6ohm. Maybe swap them and see if the error is now more downstream. Also are you enjoying the TinySA? I also looking into buy a proper SA eventually. |
| microbug:
Fingers crossed it is that. I'm now moving house and then going on holiday so that will probably be another long delay :( Yes I like the TinySA. It's a bit slow to sweep (around 5 seconds for 50MHz-4.1GHz) but it's quite usable. The touchscreen is surprisingly fast and easy to use compared to a 'real' SA. Built-in storage (microSD slot) is nice, and it comes with a 32GB card. |
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