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FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator

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TheDefpom:
In case it is helpful here is my review of this unit, I didn't see it posted in here already.

Johnny B Good:

--- Quote from: Johnny B Good on February 06, 2019, 07:52:14 pm ---
--- Quote from: Gege34 on February 06, 2019, 02:06:19 pm ---Thank you Johnny B good for the picture.

Where did you put the minus of the TCXO power supply TCXO (it's seems to go the the earth) and why there resistor (and value)?

Have you made any changes on the power supply (except the ferrite)?

--- End quote ---

 Hi Gege34,

 I used the co-ax braid for the ground return (-ve) to avoid ground loops. The white wire is the 5v feed picked up from the +5v pin on one of that group of regulator chips. The resistors you can see are a bunch of three 33K resistors in parallel using the -ve screw terminal on the module as a convenient connection point with the other end of the resistors wired to the safety earth pin on the mains socket (it knocks the 90v leakage right down to just under half a volt and neatly avoids mains earth loop issues.

 As far as the smpsu board goes, I've lost count of the number of times I've had it out on the bench for the various modifications I've tried on it. However, the first mod was to wire a 47K across the lower half of the voltage feedback potentiometer formed by the two 10K resistors between the +5v and the 0v rail to boost the 5v to 5.5v in order to raise the 11.5 volts on the "12 volt" rails to somewhere around the 12.7v mark. This wasn't quite enough, even after replacing the weedy rectifier diodes with 20A dual shotky rectifier diodes so I ended up modifying the transformer to add an two extra turns on each end of the 24v centre tapped winding feeding the 12v rails. This raised the voltage to somewhere in the region of 13.7v or so.

 In hindsight, I should have just upgraded all three rectifiers and then added a single turn overwinding to the transformer to buck the 5v winding, forcing the switching IC to compensate and so neatly increase the 12v rails without altering the 5v rail voltage and avoid modifying the transformer since there is ample room to thread (three or four lots in parallel of) the single turn of wire around the existing windings without having to remove the transformer from the PCB as I'd had to in order to to access the ends of the 12v windings in order to unsolder them from their solder tags so as to extend each winding another two turns each.

 Connecting this one turn buck winding is just a matter of lifting the anode end of the 5v diode from the board and connecting the ends in series with the diode's anode and the vacated hole on the PCB. If you connect it series aiding on your first attempt (a matter of dumb luck), all that will happen is that the 12v lines will drop in voltage, leaving the 5v untouched which simply means you need to flip the one turn winding connections round to buck the 5v, forcing the 12v rails to increase in voltage.

[EDIT 2019-03-31]

 I finally got round to undoing the original transformer mod yesterday afternoon to try out the single turn winding to buck the 5v secondary's output voltage as per the above. Not surprisingly, I had to reverse the connections to make it buck the 5v secondary.

 It worked just as I'd hoped it would. However, when it was connected 'aiding' the 5v didn't get above 3.96v (I suspect maybe due to too large a smoothing cap on the 5v rail) leaving the 12v rails  registering just over 8 volts each. Undismayed, I reversed the connections and tried again. getting +4.94v (I'd removed the 47K voltage boosting resistor), -12.98v and +12.83v. I wired in a 200K voltage boost resistor which then gave me +5.07, -13.29 and +13.13 volts which seemed to be close enough to the optimum. I didn't want to go much above the 5v mark in order to reduce the dissipation in those three very hot running LDOs on the main board and the 3.3v LDO on the 50MHz 100ppb TCXO oscillator board itself.

[END_EDIT]

====snip====


--- End quote ---

 This is just a follow up on the latest version of my PSU modification exercises showing some pictures for the benefit of anyone else who may be contemplating a similar modification. I wish I'd had this "Brilliant Idea"(tm) before I blundered in with my not quite so clever idea of adding two extra turns onto the 12v windings - it would have simplified the whole process and saved a lot of solder into the bargain. Never mind, better late than never. I guess the electronic version of the saying, "Measure twice, cut once!" must be "Think Twice, solder once!". :-[

 The first picture is a view of the overly heavy gauge wire used to overwind four single turn windings in parallel, I could have (and should have) used much thinner wire. It would have eased the job significantly but the temptation to fill that vast clearance around the bobbin overcame common good sense. :(   If I'd used thinner wire, the job of reversing the connections would have been a lot easier (I'd had to unsolder the transformer yet again just to reverse and preform the tails to go back into the hole on the board and line up against the lifted out diode lead).

 The ideal way to form this additional one turn winding is to take suitabley gauged insulated wire (in hindsight some 6 to 8 pieces of much thinner wire) long enough to let you strip only the starting ends with ample to spare to allow them to be trimmed to length and stripped once all the ends of each turn have been twisted tightly together to hold the turns in place to create a low leakage inductance link to the diode and the vacated hole in the PCB. The already stripped ends, identifying the start of each turn can then be picked out and further twisted together and tinned ready for the final connection, allowing the untrimmed ends to be likewise gathered together, trimmed , stripped, twisted together and tinned ready to make the other remaining final connection.

 Provided you've chosen a suitably flexible wire gauge, in the event that the connections need to be reversed, this final corrective task should be fairly trivial with no need to remove the transformer at this or any other stage of this modification. As you can see, I didn't choose my wire gauge wisely, making a rod for my own back when Murphy pounced.  :-[

 The second picture is an attempt at showing the connections to the PCB and the lifted up diode lead, showing just how little clearance there was between the solder blobbed PCB wire and the diode lead. I'f I'd spotted this blob of solder at the time, I would have inverted the board and sweated out that surplus solder to increase the gap (just as well it's only a matter of 10 or 15 volt peaks rather than the 350 v peaks of 240v mains).

 The last picture is essentially just a wider view to provide context (it also shows where I added the 200K resistor to lift the +4.94v to 5.07v to give a little extra boost to the 12v rails (now -13.29 and +13.13 volts with a very light loading). Subsequent testing, driving both channels into 50 ohm loads at the 20v p-p setting at 20MHz reveals a +1.8 and -1.9 volt dc offset range before any hint of clipping starts to appear on the peaks of the sine wave, a vast improvement over the original setup which had zero dc offset tolerance under the same limiting conditions.

 Also worth noting is the 1.2W reduction in energy consumption when each channel is driving a 50 ohm load at the 20v p-p setting with sine waves at 20MHz. Previously, I'd witness a power reading of 9.9 to 10 watts under these conditions whereas now it only tops out at 8.7 watts.The only way to top these consumption figures is to select the square waveform option which increases demand by another half watt.

 This final modification is in addition to the diode upgrade to get rid of the totally unsuited originals. The pair of back to back T220 devices visible in the second and in the background of the last picture are the 20A 45v PRV rated dual shotky low forward volt drop high speed rectifier diodes I used to replace the 12v rail diodes. The 5v rail diode in the foreground of the last image is a 3A Shotky rectifier diode upgrade on the original 1A rated "fast" diode it had been cursed with.

 The diode upgrades not only provide a voltage boost on the 12v rails (nearly an extra half volt) they also reduce the losses in the PSU board contributing to the overall reduction of 1.2W (about 12%) which might seem trivial but anything that reduces both thermal and electrical stress in such a compact piece of test gear is both a very useful and much welcomed side effect in this case.

HTH & HAND  :)

JBG

JBeale:
I notice that www.feeltech.net has for the past few days at least provided the less than useful response:

--- Code: ---HTTP Error 502
Bad gateway
76.115.100.230/6bedf6a
2019-04-10 00:26:25
--- End code ---

bugi:

--- Quote from: JBeale on April 09, 2019, 04:28:10 pm ---I notice that www.feeltech.net has for the past few days at least provided the less than useful response:

--- Code: ---HTTP Error 502
Bad gateway
76.115.100.230/6bedf6a
2019-04-10 00:26:25
--- End code ---

--- End quote ---
Seems to work for me right now. At least it shows something I'd expect, instead of 502.

DC1MC:
http://en.feeltech.net/ works (still 85% in Chinese  :palm:).

 Chers,
 DC1MC

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