BLM 16x16 debug

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The great design of BLM 16x16 by Andrew is certainly too microscopic (smd) for a butcher like me! :angelnot:

Andrew help me a lot for debugging some shorts.
I made a lot of tests but the BLM doesn't work:cry:.

the core is Ok , search for a Seq (send each second the same message in Mios Studio) but nothing happens when push on silicon pad (no light and no message in Mios Studio) .the core draw about 34mA (lab power supply)

i never plug it to a Seq.

i test with the minicore and a classic core with default :project.hex BLM_scalar 1.0a , no issue
so i would like to check the SRIO chain SC RC SO with an scope but i don't know the procedure!
how to check IC and shmitt trigger?


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Hi Nico,

on the SC line you should see a burst of 128 clock cycles each mS
The RC line will send a short pulse before and after the SCLK pulse
The SO line will output the patterns during the SC burst.
The SI line should send a pattern during the SC burst. It's all-1 if no button is pressed.

Testing with a scope is rel. simple: just ensure that the SC and RC signal is visible on all 74HC595/165 CLK/LD inputs.
And check that the serial inputs and outputs transfer the pattern.

If one of the chips doesn't output the pattern, it's either because it doesn't get a pattern at the input, or because a short/power problem at this IC (in worst case the IC is defective, but this would be unusual).

Schmitt Trigger: immediately forwards the input data. If you don't see any toggles at the outputs, it's related to a short/power issue.

Best Regards, Thorsten.

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Hi Thorsten ,
thanks for the procedure.
it was not the SRIO chain it was the PIC! 
it's my first totally SMT project and i take care but i think i do crappy job... find more than 20 shorts (between ground and 5v / SRIO/ leds...) fix severals shorts but some are unfixed and certainly unfixable!
i know were are the shorts but i couldn't fix it... it's a nightmare!
at the several time that i rework and rework and rework the board i damage soldermask... i've killed some pads ..etc
Andy pass several time on support with me. (great man!) i don't do honors to his great design:cry:.
i will restart with a new BLM board but with more drastic building process. i think at each solder need to be controlled via multimeter to check shorts to ground... next builders must do this process!
Best Regards, Nico

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Did you use flux to solder the SMD parts?

I bought this one: http://www.mouser.ch/Search/ProductDetail.aspx?R=8341-10MLvirtualkey59020000virtualkey590-8341-10ML and found it really easy to solder the SMD parts this way:

  1. put flux onto the pads.
  2. place the part roughly.
  3. put some (a tiny bit of) solder onto the iron.
  4. hold the part with tweezers and press down one of the pins in the corner with the tinned iron.
  5. the solder will flow under the pin. adjust the smd until everything is aligned.
  6. now you can put away the tweezers and take the solder wire. go to the opposite side of part and drag some solder over all the pins. thanks to the flux it will only flow onto the pads and under the pin. you can drag the iron up and down until the solder is nicely distributed. you can wipe the superfluous solder of with the iron.
  7. then do the same on the other side.

I have also some places on the board where the edge of the mask is damaged and exposes the ground. but with this method this was not a problem and I have not shorts.

good luck!



Edited by workspace

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Hi workspace
never use extra flux but i gonna give a try... next order...

Thanks for the tips

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