Vasile Surducan wrote:
>>> I bought the EasyProg kit from embedinc
>>> (http://www.embedinc.com/EasyProg/)
>>> and had it working for a short time. Right now the Vpp pin is stuck
>>> at 10 volts. (I checked all the lines with pic_ctrl) Does anyone
>>> know specific traces on the programmer that could cause this?
>
> http://www.embedinc.com/EasyProg/prog7.pdf
>
> Unfortunately this is a very good example about how simple things
> could be done amazing complicated. For example generating the Vpp from
> a 17V line with dozens of transistors, OA and so on,

I see 3 transistors and 2 opamps.  That's a rather small value of "dozens".
Note that there are two independent sections to drive Vpp to different pins
of the socket.  It was simpler to do that than muxing the Vpp voltage.  Each
driver is essentially an opamp with an emitter follower to give it more
current drive capability.  The resistors in the feedback loop scale the 5V
from the controller PIC output to cause 13V on the Vpp driver output.  Q1
and R1 are a simple over current sense that works thru diodes D1 and D2 to
shut down the Vpp drivers if too much current is drawn.  That could possibly
have been left out, but it makes the design more robust and I was following
a Microchip recommendation to limit the Vpp current.

> when 13.5V is
> already on the board near another chip. Guess which one ?

Oh?  I don't see any 13.5V available anywhere.  The only thing close is the
roughly 13V Vpp voltage when one of the Vpp drivers is enabled.


So whoever asked the original question, did you get your EasyProg working?
What pin on what part exactly is stuck at 10V?


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