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