Electronics > Repair

FY6900 chopped signal other issues

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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.

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