FY6900 chopped signal other issues

[cdpar2000]

FY6900 displays chopped sine wave.  See examples.  The display reads 5v amplitude, but scope shows 2v and chopped sine wave.  Other waves have same issue.  Also, when increasing the amplitude beyond 5v, a relay clicks and as I continue to increase amplitude, the signal on scope becomes more and more distorted, while measured voltage on scope reads significantly less than FY6900 displayed voltage.  This issue appears on both channels.

Additional info; board reads V2.1.   Could these issues be related to the following IC's? THS3002i (2), 4556A, AD8009(2), MCP4822E(2)?

I am a newbie, so my apologies as this may not be a new topic for the FY6900.

thanks for your guidance!
Chuck
Sacramento, CO

[theHWcave]

First thing to do is check the power rails. Are all DC voltages present and clean? Especially the +-12V (or is it 15V? can't remember) that  drive the power amp stages

[cdpar2000]

I'll check the DC power as noted with my scope.  However, notice the attached image, the power supply provides 5V's only.  By the way, this is an FY6900 60M.

thank you.

[theHWcave]

There seem to be a number of variants of this generator, some where the higher voltages (+-13.6V) come from the power supply. In your case it appears the are generated on the main board using boost converters. In any case checking that all these voltage rails are present and stable is the first thing to do. Unfortunately there seems to be no schematic available. One possible way to locate voltage rails is to look for electrolytic caps and/or voltage regulators.

[cdpar2000]

thank you.  Voltages, 5,15 are present.  I do notice a nice sine wave on input pin3 of the AD8009 (current feedback amp), while output wave on pin6 is that truncated sine wave.  There are two AD8009's, I assume one for channel 1 & 2, with corresponding pots.  It seems odd that both of these IC's would fail the same way.  I did try to remove the AD8009 from the board using a soldering iron, without luck.  I don't want to invest is a hot air de-soldering station.  At this point the FY6900 might find its way into the trash.  Although I'd like to understand its failure, I'm not sure the time, effort or expense to repair it is worth it.  I'll try adjusting the pots as a last effort.  Again, thanks for your inputs.

[theHWcave]

Well, too bad. I suspected the +-15V supply because as you say, it is very unlikely that both op-amps develop the same fault. BTW, did that suddenly happen or did you buy this unit from someone with that fault?
I have an FY6600 that has worked flawlessly for nearly 5 years now but I did replace the badly designed power supply with my own and added a thermostat-driven fan so my unit is not representative.

[cdpar2000]

thanks for the reply.  Happened suddenly.  I had replaced the power supply with a MeanWell 5V supply.  Worked fine for months.   With latest issue, I removed that supply and connected my bench PS, same issue with truncated sine waves.   Again, thank you for your replies.

[Andreas]

Hello,

did you already check the "repair sine" function in the PC-Software?
https://www.eevblog.com/forum/testgear/re-feelelec-fy6600-series-signal-generator-after-sales-services/msg2941972/#msg2941972

with best regards

Andreas

[cdpar2000]

Thanks Andreas.  Yes, I ran the software and did the "repair sinewave", with no change.

[Swake]

I do notice a nice sine wave on input pin3 of the AD8009 (current feedback amp), while output wave on pin6 is that truncated sine wave.

Is the power supply of the AD8009 ok (pin 4- and 7+)?
If yes, is the sine wave on pin3 well within the voltage of the power supply of the AD8009?

De-soldering tips:
- you need flux.
- You might want to lift the pins one by one.
- I've never used it myself but seen low temperature solder that really helps as it stays melted for a very long time.
- Or you can add a fine piece of wire and a blob of solder across all 4 pins to de-solder them all at one as this one shows from the 6:39 mark on in this video:

[cdpar2000]

Thanks for the reply.  Regarding AD8009, I've attached scope images of pins 2 (-IN), 3 (+IN), and 6 (OUT).  Pin 2 appears to be a truncated sine wave, while pin 3 looks like a complete sine wave.  Pin 6 is truncated.   Regarding the voltages on pins 4 & 7.  4= +0.33, 7=+5.  These are the exact same readings on both AD8009's.  Also, I scoped R41, which seems to feed pin 2 (-IN).  It has a complete sine wave as in input, but truncated output into AD8009 pin 2.  I measured the resistance and it read 100 ohms.  Again, exact same readings on both AD8009's and associated resistors. 

Regarding pin 4, should it read -5V?  Without a schematic, it is difficult to determine where that -5V would come from.   

again, thank you for your insights.
Chuck

[Microcheap]

It looks like your board is missing the -5V rail. You should be getting -5V at pin 4 of the AD8009 and +5V at pin 7.

My board is rev. 1.9 and it has some differences compared to yours, mine has a 79L05 supplying the -5V to the AD8009 but I can't see it on the picture you provided.

The power supply in my unit is the same as yours but it has more wires going to the main board: +5V, +5V, G, +13V and -13V. It think yours board revision uses some IC converter like LT1931 to generate the negative voltage.

Can you post a higher resolution picture of the board or at least identify those IC I pointed?

[Swake]

Microcheap is right, there is something wonky with the negative power supply and you have to find what.

A power supply component might have failed.

Or another component failed and is now a short, or almost, and is pulling so much current that the power supply collapses. This last case you can find easily with a thermal camera or a rapidly evaporating fluid such as IPA of lighter fluid. With a finger you can detect it too, but that can leave a little burn mark 

Trace back the pcb track from the AD8009 pin 4 to it's power supply. If you can, make a little schematic of what you find. On a piece of paper is good enough.

I scoped R41, which seems to feed pin 2 (-IN).  It has a complete sine wave as in input, but truncated output into AD8009 pin 2.

This might indicate that both AD8009 are dead and pull down the signal. But that seems unlikely. Let's first focus on restoring the negative power supply.

You might want trying to contact feeltech.net and ask for a schematic. They seem very professional.

[cdpar2000]

thanks.   I'll try contacting Feeltech/Feelec.  Had no luck finding links to their sites.   

[cdpar2000]

Replying to Swake's comment "But that seems unlikely. Let's first focus on restoring the negative power supply."  I noticed +5V on both AD8009 chips, but no -5V.  I found a chip, U13 which acts as a voltage inverter.  U13 = SL6KG or SGM3204.  Pin 1 shows +5v.  Pin 2 should be an output of -5V.  It shows almost zero volts.  I assume this chip supplies the -5v to the various Op Amps.  I'll order this chip and attempt to replace it.   thanks all for your feedback/guidance. 

[Swake]

Good find. Let's hope it broke 'for no reason' and nothing else made it fail.

[alonsojar]

Hi cdpar2000,
I have the same 'beauty' with the same V2.1 board level: Mine is unmodified except the front BNC connectors that I replaced by equivalent amphenol ones because center contact was failing.
By now it works as expected, so if replacing the U13 chip doesn't solve your problem and you want to investigate more, I can test in my board following your instructions (I have no idea of how this thing really works  ), so feel free to ask here or PM me.
Alonso

[cdpar2000]

Good news!    U13 SL6KG or SGM3204 was bad.  It didn't convert +5 volts to -5 volts.  Using QuickChip I was able to remove U13.  Using very fine solder and a fine soldering iron tip I was able to replace this small component. 

I'll calibrate following some good YouTube procedures.

However, I still have one problem.  The FY6900 will not produce a signal above 5 volts.  My FY6900 60M model has a 5 volt power supply.  I assume there must be some kind of buck converter chip that increases the voltage.  I don't know what chip that is, but I hope those smarter than me can help identify that chip. 

again, thanks all for the great feedback!
Chuck P.

[Swake]

Progress !!

About the output signal a manual of 2019 says this:

Code: [Select]

Amplitude Vpp
Frequency≤5MHz: 1mVpp~24Vpp;
5MHz<Frequency≤10MHz: 1mVpp~20Vpp;
10MHz<Frequency≤20MHz: 1mVpp~10Vpp;
Frequency>20MHz: 1mVpp~5Vpp;

I don't know for sure if this applies to your version or not, but let's assume it does.

Have you tried with a low frequency sine signal of let's say 100 Hz?
Did that signal show up on your scope as expected, no more distortion?
What is the output Vpp setting on the generator? What is the measured value on the scope? If it is not the same please experiment a bit a try to find the limits or a correlation between the 2.

[alonsojar]

Hi,
Maybe chip U11 RY1303A is the one you're looking for, but is so tiny that even test it with a multimeter probe is difficult at risk to touch two pins and create a short.

https://www.rychip.com/en/pd.jsp?fromColId=130&id=510#fai_14_top&pfc=&_pp=130_509

I see they are selling in aliexpress but unsoldering and soldering can be a challenge and will require a hot air gun and some experience IMO.

Good luck!

Edit:I've found the RY1303 datasheet and it's a step down buck converter, so probably not part of your problem.
https://www.lcsc.com/datasheet/lcsc_datasheet_2410121523_RYCHIP-Semiconductor-Inc--RY1303_C370881.pdf