What is so critical of calibration part of PICKIT2 that we can't realise it?

[mvs sarma]

i have made a local through hole version of PICKIT2 in full
compared to Microchip original, the status of yellow lamp glowing little longer before the test blinks are found, and finally it puts a message that

"VDD voltage level ERR. you may check the target and ...."
when we go to calibration, the calibration passes. while doing trouble shoot, the Vdd set to 5V reads only 4.6V balance dropped across D4 ( the input of D4 being close to 5V). the pickkit2 measures 4.9 for 5V instead.
the microchip forum indicates that some programmers made before Sept 2006 or so, D4 was to be changed.
they suggest ZXCS1000, an SMD part schottky diode of 1000mA, and .35V drop at 1 amp load. we try to pick a least forward drop diode from a batch of 1N5819.

Polarities of FETs and Transistors etc taken care by actual test by DMM instead of datasheet or imagination as we get BS250 with no maker's logo.
a tentative drawing is attached for discussion. Request for comments and suggestions.

 

[mvs sarma]

Solved the case by a buffered supply to the board. However, with the same power supply from PC the microchip Pickit2 is working comfortably.

I have applied external supply to the pickit2 board and the supply coming from USB cable is disconnected and used to glow a RED LED in order that the PC recognizes the pickit2.

Thanks to all who tried to study my problem. Still the issue is open as i have only circumvent the issue.