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| FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator |
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| aimc:
--- Quote from: rhb on September 29, 2019, 04:40:08 am ---I don't understand what you're showing. Is the sweep synchronized with the scope trigger? Also please take a look at the PCB. Is there any flux residue visible? Flux absorbs moisture out of the air. This results in an environmentally dependent parasitic capacitance. It would not take much capacitance to cause the drop in output you're seeing. If you see any flux, clean it off with isopropyl alcohol and an old toothbrush and retest. I've done quite a few repairs, including an HP 34401A which had been repaired previously that consisted of nothing but cleaning flux residue off the board. The 34401A was completely non-functional until I cleaned it. But after cleaning meets the factory spec. It's the more accurate of my two 34401As. The other one was a closet queen and saw very little use. Have Fun! Reg --- End quote --- Sorry, I did not describe the attachment. Well, essentially both images show a periodic ~0.5s sweep from 0.1-60MHz (left to right), one in the time and the other in the frequency domain. An yeah I triggered on the edge where 60Mhz jumps back to the higher amplitude 100KHz to keep the presentation stable (although I stopped it anyways later). The interesting part is in the envelope, which gets kind of jaggy, likely due to the sampling lag between the much finer FY6800 sweep increments compared to the scope acquisition speed. I can show that along the time axis the amplitude decline becomes visibly discretized into stair steps when you crank up the scope's front end amplification (not sure, but this also may saturate the amp, that's why I didn't show it). The other screen shot shows the FFT of the FY6800 waveform during the same frequency sweep at much faster time base. Time base has to accommodate sufficient sampling to provide a decent time resolved FFT window, small enough to approximate it as a single tone at each time base sweep. Then, as the tone frequency slowly sweeps from acquisition to acquisition, with the FFT set up to keep only the maximum of the peaks you see a decent magnitude over frequency representation. This will take some time and acquisition sweeps until all maxima form a solid line. With the cursors set to the math output, you can quantify the roll of. When you compare both screen shots you see the expected similarity only different by the different log scale from the FFT (which I chose to show dBv units). The two representations also compare quantitatively pretty good within a reasonable margin of error. Hope this explains my measurement steps. I will have a look inside the AWG and look at the solder connections. Thanks for this advise :) Regards Lutz |
| CDaniel:
I supose you have another generator that is linear as you want , otherwise you don't know where the problem is . |
| rhb:
I'll post a quick comparison of a Keysight 33622A and an F***Tech FY6600 with V 3.1 FW once I clean up a bit. The 34401A is the most spectacular example of the evils of flux residue. When it arrived, it just displayed random digits on all functions and ranges. I opened it up and saw a 1 cm brown spot around where an LF357 had been replaced. I sprayed it with 91% isopropyl alcohol and scrubbed it with an old tooth brush, checking with a magnifying glass to make sure I got everything off. I then dried the board with a hairdryer. When I powered it up it worked flawlessly and still meets factory spec on the 10 Vdc range checked against two very high quality LTZ1000 voltage references. I've "repaired" several TV remotes, a CD player, DVD/VCR player and other things this way. In the case of the CD player, I didn't get all of the residue off the first time. About 6 months later it started acting up again ("NO DISC"). I cleaned it again using lots of alcohol. Haven't had a problem with it again in several years. I think the flux I missed was underneath the MCU chip. The only residue on the board had been a small spot near one corner of the MCU. The 91% IPA from the supermarket is not very pure, so blotting excess off with a towel is important. Otherwise you will have s white film of something left behind. You can see minute amounts of flux with a 5-7x magnifier by looking at the smoothness of a reflection from the board. It's not uncommon for me to find that after an initial cleaning and drying. If I see it, I do it over. Have Fun! Reg |
| aimc:
--- Quote from: CDaniel on September 29, 2019, 04:59:06 pm ---I supose you have another generator that is linear as you want , otherwise you don't know where the problem is . --- End quote --- No, not really - only a cheapo AD VCO development board that goes from 35M-4.4GHz. I do know the response of the scope (with and without probe) though and hope to find the problem with the scope only. Frequency range is rather low, so will try to tap in before the amp of the FY6800 if I find a good location to do so. |
| rhb:
Here are a couple of screen shots. The FY6600 V 3.1 sync output when sweeping it being swept :-( Makes it useless. As a result, the only way to trigger on the sweep is the drop in output. Sweep is 10 kHz to 60 MHz for the FY6600 and 1 kHz to 60 MHz for the 33622A. Scope is an Instek MSO2204EA with 50 ohm thru terminators. Signal amplitude is 200 mVpp. First the 33622A. Note that it has some signal drop as the frequency goes up. Not sure what the culprit is. I'll investigate. Then the FY6600 which has much more drop. I think the biggest FAIL is the sync signal not being the start of a sweep. I spent some time trying to get proper synchronization on the F***Tech, but could not find a way to do it. So I set a rising edge trigger on the signal at the 10 kHz end above the level at the 60 MHz level. I bought the 33622A used from Keysight on ebay for 30x what the F***Tech cost. Older HPAK AWGs were so expensive on ebay that they didn't seem to make sense. The 33622A goes to 120 MHz and is quite amazing. I bought it because my F***Tech was dead. F***Tech made promises but did not deliver. My choices were more Chinese which did not fill me with great confidence or a 15 MHz HP for $500. So I went with the 33622A. I'm glad I did. And glad I could afford it. I've got an HP 8560A and a 438A, so I have other test options. I'll see if I can use some of the other F***Tech rear panel inputs to synchronize the two AWGs and overlay the sweeps. Have Fun! Reg After I posted this, I noticed that the sample rates imply aliasing, so I'll need to examine that. I suspect that sweeping over such a wide range into a DSO is not a good test. So I'll try repeating with my Tek 485. |
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