PreenFM > preenfm2 and preenfm3

Strange behaviour starting up

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Soop:
I have been checking points with a multimeter from a picture in a previous post (thanks Xavier - really helpful!). Am powering with USB via a MacBookPro to test.

Everything seems ok except the two points coming down from the OLED header connection (next to the 100nf cap, close to the 6N137), which show only 3.47v - I believe it should be 4.2v rather than 5v with the 22ohm resistor?

I also noticed that the display changed to blocks while I was testing. I even tantalisingly got the correct home screen for a brief moment before it disappeared - so close! Really looking forward to getting this excellent synth going so fingers crossed for tracking down a solution and I will share as it might help others who come across this issue.

By the way, this forum is a really great resource - many thanks!

Xavier:

The 3.47v can be because the blue oled draw more currant than the yellow.
You can try a smaller OLED resistor or simply shortcut it to check if that solve your problem.

You should also resolder ALL your junctions related to the OLED. There seems to be too much solder.
https://learn.adafruit.com/adafruit-guide-excellent-soldering/common-problems

Try to resolder the 16 on the PCB, the 16 on the display and the 20 upper points of the preenF405.
Put your hot iron on each point and wait for the small ball to melt and go down.

Xavier

Soop:
Thanks so much for your advice, Xavier! I really appreciate you replying so quickly.

Apologies that my very basis skills caused a problem. Actually I wondered whether the connections were not good so added more solder - obviously the wrong way to go and not very helpful! I will try these ideas. Thanks again.

Soop:
I resoldered my blobby joints but interestingly disconnecting the OLED resistor has got it working! Phew!
Some pages slightly dimmed on the screen. I will try a lower value resistor or a jumper when I have time later. Then audio...
Thanks again!

Xavier:

--- Quote from: Soop on September 26, 2019, 01:22:07 PM ---...I will try a lower value resistor or a jumper when I have time later. Then audio...

--- End quote ---

The "Led"  is the Display power connection.
So it must not be empty or it won't work correctly.

The 22ohm allow the "Yellow OLED hiss mod". Not sure it's still usefull with the latest BLUE OLED.

You can just solder a resistor leg instead at the "Led" points.

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