Friday, May 22, 2015

One small step away from fixing the FPGA board and resuming testing of the SAC Interface


I contacted the fpga board vendor to see if I can modify the order before shipment to switch to express delivery, 2-4 business days. Fingers crossed on this one, as it would get me back in testing mode much sooner.

I next set up my lighted magnifying lens and looked more closely at the board, in conjunction with the schematics and the fpga pin assignments, in order to see what possibilities might exist for repairing the damage.

I found that the signals going to the flash chip are accessible on leads around the outside of the USB module nearby on the board. I first did some verification of the connectivity and correctness of my information. With that verified, I could solder the flash chip to the 7 remaining pads. The final step was to solder on a bridge or jumper wire between pin 2 of my flash chip and the appropriate pin on the USB module.

Tacking the 30 ga wire wrap lead to the pad of the flash chip was easy. The tough part is getting the wire soldered onto the lead of the USB chip. The leads are .012" wide with just .014" gap between them. The copper wire is .01" diameter which is an appropriate width but alignment has to be pretty accurate. If I am off more than one hundredth of an inch, I will be touching an adjacent lead.

This evening I received, not a response to the emails I sent about changing the shipping, but an automated confirmation that the board has shipped the old, slow way so that I won't have it until near the end of June. Disappointing and it makes the need to fix the existing board all the more urgent if I am not to incur a long enforced holiday from the testing.

I tried quite a few ways, but the real limitation is my eyesight. None of the magnifying lenses and lights I have allow me to see a 1/100' inch copper wire on top of a green coated PCB, at least not well enough to be sure of the contact, angle and to allow me to touch solder a .01 x .01 spot. I can use various clamps and jigs to hold the board and the wire, but if I am not sure that it is in contact with the lead properly and not able to see where my soldering tip is placed, I am not going to be able to get the wire tacked down.

This may require an investment in a stereo microscope to allow me to proceed. Tomorrow I will give it another try with the best magnification gear I can set up, before I have to go buy a microscope.

1 comment:

  1. Instead of a "real" microscope, how about a USB one? "USB microscope" at amazon turns up a bunch of hits, (like ) which has a stand so you could use it hands-free. Much cheaper at any rate.