Howto, Repairs

KA630 Console Bulkhead Dead LED Output Fuse Fix

If your KA630 seems to work OK but the console bulkhead LED display is dark, the issue is probably only a burnt-out fuse. A result of a short circuit, probably somewhere on the bulkhead, that may have happened a long, long time ago.

Instead of de-soldering and pulling out the old fuse, thus risking mechanical upset to the delicate PCB traces, here is a less intrusive procedure which uses a small SMD fuse. Do not simply short the burnt-out fuse using a wire, fuses are always there for a reason.

What you will need:

  1. Soldering equipment,
  2. Some wire-wrap wire, and a wire cutter
  3. A small 1A fuse (I used a Bourns p/n SF-126SP100-2 , a 1206 1A, slow-blow fuse)
  4. A MicroVAX II KA630 (M7606) Qbus CPU with a non -working console LED output

Step 1: Locate the fuse and test it for a short, making sure it is indeed blown

(the procedure  below shows the Rev 02 board fuse location, Rev 01 board fuse fix is shown at the end)

Step 2: Solder a wire-wrap (single-conductor) bare wire across the fuse

Step 3: Cut the wire in the middle

Step 4: Center and bend the wire ends, then place the fuse so that it touches both

Step 5: Solder the fuse in place

Rev 01 board before- and after- photos: