CH341A Pro Serial PROM Programmer mods

The CH341A Pro Serial PROM Programmer is low cost programmer based on the CH341 USB Serial chip with special protocol modes for I2C and SPI.  A good source for the hardware info for the programmer is here. 

Some of the modifications are well documented on the eevblog. I cleaned up the mods and added a few.

Programmer modified for 3.3V

The programmer is modified for 3.3V I/O voltages as the ZIF socket is wired for 3.3V (see J3).

• Vcc at pin 28 - connected to 3.3V (Required).  The CH431 chip I/O rail is set to the 3.3V supply from U1.
  
  

  

  Modification to PCB
  
  

  

  Side view of the modification
  
  

• V3 at pin 9 - connected to 3.3V (Recommended by datasheet).  The internal 3.3V regulator for USB should be connected to the external source if Vcc is running from 3.3V.  I have measured the voltage at V3 and it is pretty closed to 3.3V, but modified it anyways as it is easy.
  

  

  V3 connected to metal tab of U1 - 3.3V regulator output

  
  
  
• RN1C - connected to 3.3V (Optional).  The power LED (D1) is too bright because it is connected to 5V instead of 3.3V like D2.  The power LED now has similar brightness as D2.

Top trace: Resistor pack pull up that was connected to 5V
Bottom trace: 3.3V from U1 regulator

I have made a small plug for the programming cable using a protoboard.

I have replaced the spring for the clip-on programming cable as it is too strong and bent the pins on some of my chips.

Original spring (Bottom) is replaced with a weaker spring (top) from my junk box.