Monday, May 28, 2018

Snail like progress finishing up the Documation card reader USB interface conversion


My right angle cables arrived tonight and I carefully installed one to test out the board fully installed in the card reader. The right angle cord is just perfect, leaving plenty of room for the main connector to the card reader.

Right angle cable provides the clearance I needed
Still, with this board in which I had twisted the socket to restore USB connectivity, I had erratic connections. The reader did pick and read two cards, but kept dropping the PC connection. I have to wait for my new FTDI USB daughterboard and install it before I can be sure that I have any problems other than the flaky board connectors.

Meanwhile, I found a new mini-USB socket in my parts bins, spurring me to solder it onto the second interface card with the previously dead FTDI USB daughterboard to permit me to use this with the other (600 cpm) reader I own.

My solder paste is all stale and dried out, otherwise that would have been the ideal mounting approach. Put paste on the five leads and four grounding pads, then gently heat with the hot air gun until the connector snaps into place on the molten solder. Surface tension is a wonderful thing.

Instead, I had to hand solder this into place. It was very hard because the five leads from the socket do not extend out past the overhang of the connector body, making them very hard to see and reach with a fine soldering gun tip.

I was able to get the connector aligned properly and the ground pads soldered, to hold the connector to the board (as well as these ever hold, which is . . . not very). The challenge then was to get the four active leads of the five soldered to the board traces. The leads are +5, D+, D- and ground, plus a n/c trace.

Unfortunately, one of my four required traces lifted - the D- signal - requiring me to try to do an emergency fix. If I can locate the D- signal elsewhere on the board, I can do a very fine jumper wire from pin 4 of the socket and restore operation. Otherwise, this is truly dead.

Fortunately, I found a 270 ohm resistor that sits between the D- pin of the socket and the D- pin on the FTDI 245BL chip. It is close to the connector, which gave me the chance to tack on a very fine jumper wire and repair the board.

Upper right oval is missing trace, lower left is resistor pad for D- signal
In the picture above, you can just barely see the pin of the connector peeking out, at the very top of the red oval. I had to tack a wire to that pin, then tack the other end to the circled resistor end. If I could achieve the connection to the socket pin, the rest would be easy. 

A blob of solder formed underneath, spanning three of the socket pins. I had great difficulty trying to extract it and wasted 45 minutes fooling with it. I finally decided that the time involved was excessive, given that I had replacement daughter cards on the way which would give me a more solid and reliable board than likely with this fix. 

No comments:

Post a Comment