Products > Test Equipment
FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
<< < (385/450) > >>
Johnny B Good:

--- Quote from: MikeLud on August 03, 2019, 04:27:44 am ---I need some help with my FY6800 power supply upgrade. |O I did most of the upgrades shown in this schematic https://github.com/DerKammi/FY6600-15-30-50-60M/blob/master/Hardware/FY6600%20PS%20schematic%20V1.pdf. The only difference is I did not change D9 and instead of changing R6 I replaced the two 10K voltage divider with a 20K Multiturn Trim Pot wire the same as a voltage divider so I can adjust the output voltage. Also instead of using a 68uF 400V for C2 I used a 33uf 400V. Now the FY6800 intermittently turns on by having to turn it on and then off several times using the switch in the back. When it does turn on it works fine, with the power supply voltage at -13.6V, +13.5V, and +5.0V. and the on/off button in the front work fine as long as I do not turn it off with the back switch. Any help will be appreciated.

Thanks,
Mike

--- End quote ---

 Hi Mike, and welcome to the FY66/68 hundred modders' house of fun and pains. >:D

 I had several criticism regarding those modifications when I looked them over for inspiration on 'improving' the PSU board in my then newly acquired FY6600-60M way back in November last year just before I made my very first post to this forum. I've inserted a link so you can see my initial modifications to the PSU board (I've lost count of the all the other mods I've tried with that PSU since then).

https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg1973777/#msg1973777

 For starters, the value of the mains smoothing cap was over-specified by almost a factor of seven. The original 10μF 450v is entirely adequate for a 10W rated smpsu designed to operate on mains voltages in the 86 to 365 vac range (1μF per watt appears to be based on a universal design rule for all such universal mains voltage smpsus - I've yet to come across any exceptions to this 1μF per rated watt rule).

 If you're only using it on 220v or 240v mains supplies (the harmonised 230v mains specification in all its guises of practical reality) without any thoughts of ever using it on 110/120v supplies, there's absolutely nothing to be gained by such an 'upgrade'. Indeed, the reduced voltage rating from 450 to 400 volt of the suggested replacement places the logic of replacing the 220μF 16v caps on the 12v rails with 25v rated 220μF caps in some doubt.

 Whilst the 400v rating is perfectly fine for this task, the voltage rating upgrade on those 16v 220μF caps would equate to increasing a 400v smoothing cap to 625v (or the original 450v cap to a 700v rated one - it makes very little sense when the PSU is operating under its designed conditions (never disconnected from the load whilst powered up for prolonged periods of time) to uprate those output caps to 25v. A far more useful upgrade would be to replace them with 470μF 16v caps - the voltage isn't the issue here (it really isn't - trust me).

 However, when it comes to improving the smoothing on the 5v supply, it can be all too easy to get carried away (replacing the 470μF with an 1800μF 6.3v cap and replacing the 220μF with a 1000μF 6.3v cap) and overload the dinky little high voltage switching IC on startup causing it to sulk in a shutdown standby state. In the end, I landed up reducing these capacitor upgrades in two stages before I could eliminate the hot restart issue that had appeared after I'd cured the cold startup issue. Effectively, I'd dialled back the 1800μF to a mere 1000μF and restored the original 220μF.

 You could say (as indeed someone did) that I'd upgraded it to 'capacity'. If I hadn't already upgraded the 12v rail caps to 470μF ones, I might have gotten away with the 5v rail capacitor upgrade. However, using up my capacity margin on the 12v rails was the best option anyway - less ripple on the analog supplies (all derived off the 12v rails) where it really matters - the 5v rails can go hang, it's only used to power the three LDO regulators anyway (3.3, 2.5 and 1.8 volt rails) on the main board.

 The diode upgrades are a definite requirement to both improve the 12v rail voltages and the efficiency of the PSU (apropos of which, install a small cooling fan if you don't want to be faced with a recapping job in 12 to 18 months time - the vent slots are counterproductive to passive cooling, a small vent fan is an absolute must imho). If you read that first posting of mine, you'll note I went a little overboard on the diode upgrade (well, I had them to hand, so why not already? :) ).

 Much later on, I'd worked out an optimal solution to increasing the voltages on the 12v rails far more effectively than my 47k 10% boosting bodge on the 5v rail to likewise boost the 12v rails (over and above the extra two turns I'd added to each of the two 12v windings I'd applied in a previous modding session). ebel0410's mofification to the voltage feedback network raised a wry smile by the fact that he'd made more work for himself by removing R6 and replacing it with a 12K rather than use the quicker and slightly more effective shunting of the other 10K in the voltage divider with a 47K to get virtually the exact same result. When it comes to this sort of modding work, there's usually more than one way to skin the cat. >:D

 You can view my description of my final PSU mod here:-

https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg2310768/#msg2310768

 And, you might find this earlier posting of some interest too.

https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg2182397/#msg2182397

 For all its faults (high ripple noise - on a par with any commodity smpsu to be fair), the one thing Feeltech's tiny smpsu board doesn't suffer from is imbalanced current output ratings on its +/-12v rails, unlike every single example of dual rail commodity smpsus I've ever seen on Ebay (whether just a naked PCB or an enclosed unit).

 Looking on Ebay for dual rail smpsus designed to satisfy the requirements of dual rail opamps is on a par with tracking down Unicorn droppings (never mind the Unicorns themselves! >:( )  Typically, such small dual rail smpsus will specify a +12v rated at 600mA whilst the -12v rail is only rated for 150 to 250mA at most, often with the requirement that the +12v be loaded to a minimum level to bring the -12v to within 10% of its nominal voltage spec.

 Mind you, if you happen to be planning on adding a 12v 10MHz OCXO (with a 3N502 clock multiplier chip replacing the shite smd XO chip on the main board), such an imbalanced spec might be just the ticket!  >:D

 Obviously, there are suitable smpsu modules available which have balanced ratings and very low switching noise but you won't find any on Ebay. You have to deal with the manufacturers or their agents directly and put in a request for a quote on pricing and you know what they say about that... "If you have to ask, then you probably can't afford it." :(

JBG
MikeLud:
I decided to go with replacing the SMPS with a linear power supply. I found a LM317/LM337 and LM317 linear regulator in country at a reasonable price, below are the links to the ones I will be using. To feed the linear regulators I am going to use a 30W R-Core Transformer 15V+15V 9V+9V.

https://www.parts-express.com/adjustable-voltage-regulator-power-supply-board-----125v-to-37v-dc-output-lm317-lm337-desig--320-616
https://www.parts-express.com/positive-voltage-adjustable-power-supply-board-ac-dc-in-dc-out-based-on-lm317t-regulato--320-614

Thanks,
Mike
Johnny B Good:

--- Quote from: CDaniel on August 03, 2019, 06:11:02 am ---I don't think that power supply is worth upgrating , just replaced with a linear one .
Anyway you should measure your pot resistance and see if  it works ok with the old value 10k , in a such SMPS you can't change the voltage by much or could become unstable . Even if it's 12K as the autor say it works , because of various tolerances is not certain that in every case  will work

--- End quote ---

 The analogue psu can be an effective solution but the downside is that you'll introduce greater thermal stress than the original (typically 70 to 80% efficient) smpsu board on the unit if you neglect to add a cooling fan to prevent an already hot running generator from overheating. Preferably a fan that offers a further reduction in temperature to extend the life of the components, most notably that of the 105deg C rated caps.

 Indeed, a few of the homebrewed analogue PSU projects have suffered regulator failures for lack of heatsinking, in some cases to the detriment of component failure on the main board (a brand new THS3091 burning out forcing the owner to revert back to the original THS3002i chip for lack of a spare 3091 being one notable event).

 If you're going to build a custom analogue psu, you need to be very mindful of this thermal issue. A fan is a must have item, even before you add the additional heat from an analogue psu, imho. IOW, make adding a cooling fan you first priority before doing anything else (after allowing a period of grace to allow any faults to show up before voiding the Chinese warranty, of course :-DD).

JBG
MikeLud:
JBG,

Thanks for your advice, I will be adding a cooling fan. Once I finish the PS upgrade I will be upgrading to a D75J and THS3091.

Thanks,

Mike

CDaniel:

--- Quote from: Johnny B Good on August 03, 2019, 11:05:23 pm ---
--- Quote from: CDaniel on August 03, 2019, 06:11:02 am ---I don't think that power supply is worth upgrating , just replaced with a linear one .
Anyway you should measure your pot resistance and see if  it works ok with the old value 10k , in a such SMPS you can't change the voltage by much or could become unstable . Even if it's 12K as the autor say it works , because of various tolerances is not certain that in every case  will work

--- End quote ---

 The analogue psu can be an effective solution but the downside is that you'll introduce greater thermal stress than the original (typically 70 to 80% efficient) smpsu board on the unit if you neglect to add a cooling fan to prevent an already hot running generator from overheating. Preferably a fan that offers a further reduction in temperature to extend the life of the components, most notably that of the 105deg C rated caps.

 Indeed, a few of the homebrewed analogue PSU projects have suffered regulator failures for lack of heatsinking, in some cases to the detriment of component failure on the main board (a brand new THS3091 burning out forcing the owner to revert back to the original THS3002i chip for lack of a spare 3091 being one notable event).

 If you're going to build a custom analogue psu, you need to be very mindful of this thermal issue. A fan is a must have item, even before you add the additional heat from an analogue psu, imho. IOW, make adding a cooling fan you first priority before doing anything else (after allowing a period of grace to allow any faults to show up before voiding the Chinese warranty, of course :-DD).

JBG

--- End quote ---

Yes , I know , or you could build the supply in an external box . Could be easier this way , you don't have to find the right size transformer .
Mine is inside and gets hot , for stand-by I found a signal from the microcontroller in the front display board that's switching a relay so +15V and -15V are disconnected. If not , in stand-by the analog part will still consume a lot of current ... no shut down feature was implemented in the original design .
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod