At 05:45 PM 1/28/2008, Martin Klingensmith wrote: >What made wire-wrapping necessary on something required to be so highly >reliable? Yes, I know wirewrapping can be reliable but it seems as >though through-hole PCBs are about the most reliable construction method. The PCBs were as you described. It was the backplane itself that was wire-wrapped. Sort of, that is. All of the edge connectors had long wire-wrap pins for the connections. The power rails were busses with formed pockets that were pushed onto the pins. The push-fit was obviously deemed not adequately reliable because they had been soldered in place during manufacture. Most (all?) of the leads leaving the backplane used a funky spring clip that held the wire tightly against the pin. I *think* it was the AMP Termiclip family. I'm not sure if *any* connections were actually wire-wrapped - I don't remember. Its just that the edge connectors used wire-wrap pins. It was those pins that were sprouting whiskers. Yeah - those edge-connector pins were tin-plated instead of gold-plated. Note: the contacts that mated with the PCBs were gold-plated. It was just the wire-wrap pins on the backsides of the edge connectors that weren't. Quite frankly, that was the only thing that detracted from this obviously high-quality piece of equipment. Seriously high quality: mil-spec everything: from the pots to the op-amps to the solid slug (wet) tantalum caps. Not a single conventional electrolytic cap to be found. Film caps everywhere. They had sent me a complete set of spare PCBs to examine and repair if necessary. I built simple test jigs that let me test the functionality - everything tested good. Trim pots were all OK (a real surprise!) - not noisy at all. All of the active components tested OK. Thus the trip out to the plant. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist