Michael Neary wrote:
-------------------------------

Which programmer are you building?

I am working on the latest version. In fact about a year back Asim had emailed me the Orcad schematic. This I converted to a single side PCB. However I have made some changes e.g. using 317 instead of 78L05. I believe this schematic was of the original 1.1 version.

Yesterday during static testing I removed the resistor in series with the diode D3 (which switches VCZ to the VPP line). The voltage is now 4.3V at H.

Today I am going to test another idea regarding fanout. Bit D1 and D7 are facing a fanout of 4 and 2 respectively. It maybe that the port chip inside the laptop cannot sustain such a fanout. D1 seems particularly important given that it is connected to the clock inputs of all the chips. What I am planning to do is to insert U3 (and maybe U1) and see if the control functions work i.e. VCE, VPS etc. go up and down. If fanout is an issue then insertion of the other chips should freeze up the functioning.

It encountered this problem while building a serial port programming device (also given on the kmitl website). I made it work by adding a couple of transistors as buffers. The same problem may be operating here.

Regards

Aurangzeb