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I have a control board with a microcontroller in BGA package. I need now to measure a signal on some microcprocessor's output pin. The problem is that there is no test point around the microcontroller on the PCB. Does it exist any possibility how to get to the output pin without a test point? Thanks for any advice.

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  • \$\begingroup\$ Is there no trace at all coming from that pin? \$\endgroup\$ – Roger Rowland Oct 5 '16 at 12:23
  • \$\begingroup\$ The only way is to find some trace that that particular pin is attached to, and somehow get a probe or wire on it. If there is no trace, you're SOL, as the pad is under the chip \$\endgroup\$ – Scott Seidman Oct 5 '16 at 12:24
  • \$\begingroup\$ Can you use pin-mapping to assign the logical output to a different physical pin that is accessible? \$\endgroup\$ – Steve G Oct 5 '16 at 12:38
  • \$\begingroup\$ Depending on how much effort you want to invest and what tools you have available: You could do a dead bug solder \$\endgroup\$ – Botnic Oct 5 '16 at 12:45
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    \$\begingroup\$ If the pin's on an internal ring, that's some skilled dead bug work! \$\endgroup\$ – Brian Drummond Oct 5 '16 at 12:46
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Does the control board have JTAG? JTAG offers "boundary scan", a way of determining each and every input and output pin on the chip - plus the values of internal registers and all sorts of other things. Of course, it means you need it connected to the JTAG chain, and a JTAG connector, and a JTAG probe, and software to drive it.

Otherwise, @ScottSeidman is right: you're out of luck.

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  • \$\begingroup\$ Problem is that I am not able to establish a connection between the microcontroller and the emulator. I need this measurement for troubleshooting regarding JTAG. \$\endgroup\$ – Steve Oct 5 '16 at 12:44
  • \$\begingroup\$ That's the worst! Debugging the debugging mechanism! I feel for you - but I have no more suggestions. \$\endgroup\$ – John Burger Oct 5 '16 at 12:46

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