[Usbpicprog-technical] Troubleshooting a low Vpp

[David <dev...@fo...>]

Hello everyone!

I'm trying to troubleshoot a low Vpp on my usbpicprog v0.3 hardware.  I'm
only getting about ~10.78V with no load attached.  USB supply voltage is
4.98V.

I'm getting a solid 13.25V on the pump side of R1, with only a 0.17V drop
across it, confirming little load.  However, by the time I get to the Vpp
header, I'm showing only 10.79V.  The anode of D4 is also low at 11.27V.

Unfortunately, the board I have (SMT version, pre-assembled) doesn't exactly
match any of the schematics.  I have what appears to be a Q5, and R13 is not
assembled (which is what the v0.3.1 hardware calls for), yet I still have
the 47k and 100k R16/R15 voltage divider on the Vpp sense (v0.3 design).  I
also have no D10.  So, thus far, until I trace Q5, I'm a bit of a loss to
troubleshoot further.

FWIW, my Vpp may have always been low -- I recall having some issues reading
a device a while back, but I moved the interface to a powered hub and all
was well.  I didn't investigate further.  Now I'm on a powered hub and I'm
unable to get a PIC10F206 to respond, which I'm assuming is because Vpp is
well below spec for program mode entry.

Any thoughts?

Thanks!

David