Electronics > Repair
FY6900 chopped signal other issues
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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  >:D

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.


--- Quote from: cdpar2000 on January 04, 2025, 09:52:47 pm ---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.
--- End quote ---

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. 
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