AstraDome Amp Gauge Problem and Repair

By Dave Mason


Symptoms:

Smoke from somewhere around instrument cluster.

Gauges reading all the way high.


Troubleshooting:

Because the gauges were reading all the way high, I was prompted to inspect the grounding. The original ground wire looked burnt. I checked continuity of Astradome gauge housings to ground and found they were not grounded. I disconnected the battery, made a new ground wire, installed it, checked continuity of housings to ground, and reconnected the battery. More smoke. I disconnected the battery again, inspected the new ground wire and found it to be burnt. Because the heavy gauge wire feed to the amp gauge is always hot, I suspected a problem here, and checked continuity of amp gauge voltage feed posts to ground and found continuity. This meant that the hot feed to the amp gauge was being grounded out which made sense to explain the burnt ground wires.

Repair:

Upon removing the amp gauge and inspecting it more closely I looked for any place that carries voltage that should be insulated from the housing.

The threaded posts are essentially a pass-through of current flow (in one and out the other), and the gauge indicates direction of current and relative amount. Therefore the gauge housing (designed to be the ground) must be insulated from any part of the gauge which touches the hot voltage. Here are the points which need to be insulated:



There was no visible problem to be seen here except
that the gauge posts were not aligned parallel to the housing:


I therefore needed to get a better look into this area.
I found that one of the posts was touching the gauge housing.

So this post needed to be pushed away from the housing.
I did this with a vise using a nut to push.
Why did I need this method to straighten the posts up?
Difficult to do by hand because of this soldered structure support:

After straightening the posts and looking closely, although they were now pretty well
centered in the holes, the tolerances are close in the gauge design so rather than take a chance,
I unsoldered the circled joint and disassembled the gauge, then used a
round chainsaw chain file to enlarge the holes slightly:

Note: I did not need to unsolder the
electroluminescent lighting wire circled here:

After enlarging the post holes a little I reassembled and resoldered the joint.
Now the posts have a little more clearance in the housing holes.

Because there are metal split ring washers pressing directly on fiberboard, I added some flat stainless washers to prevent a metal split ring edge from digging into the insulating fiberboard:

Snugged up the nuts carefully and re-checked continuity between the
posts and housing and had none, which is what you want, meaning the
housing is properly insulated from any hot voltage points.
Repair complete.
John Grady suggests that the repair can be made even better by
using weatherstripping adhesive around the
posts at this stage before re-assembly:
I did not use the weather stripping adhesive on this repair
but I probably would use it if doing another one of these
repairs as an extra safety measure.


Thanks to John Grady for input and assistance!