"Terry Coombs" wrote in message
...
On 9/24/2019 9:04 AM, Jim Wilkins wrote:
"Terry Coombs" wrote in message
...
When I got my truck back from our son , lots of things that he
just
couldn't be bothered to fix . One thing is the radio power supply
.
He did tell me that the radio had "died" , turns out the fuse (in
the fuse block) keeps blowing . I've got the dashboard apart
enough
to check the wiring harness and supply wires , can't find any cuts
or anything that looks like damaged insulation ... it works just
fine sittin' in the driveway , but within a few miles driving it
blows the fuse . I figured it was the radio/CD player unit so I
got
a new one , does the same thing . I'm really puzzled by this ,
from
the way the fuse was spattered it's got to be a dead short to
ground
. I think it very unlikely that the new radio/CD unit is bad - the
old one did work when I replaced the fuse , for a few miles same
as
the new unit . This is an '86 GMC pickup , I'm hoping someone here
might be aware of a known problem area that I might check ... I
gotta have tunes !
--
Snag
Yes , I'm old
and crochety - and armed .
Get outta my woods !
Check/clean the battery connections.
If connector vibration momentarily disconnects the battery from the
charging circuit, the alternator output voltage will rise until a
protective clamping device somewhere, like in the radio, conducts
enough current to limit it. The voltage regulator tries to cut off
the
alternator field current but can't remove the current already
flowing
in the field winding.
https://en.wikipedia.org/wiki/Load_dump
Wouldn't that blow the smaller fuse in the radio itself before the
15 amp supply fuse ?
--
Snag
Yes , I'm old
and crochety - and armed .
Get outta my woods !
Hard to say without looking. Some fuses blow immediately, others have
a time delay to allow high-current startup surges like charging the
power supply capacitors. For example I can pull 70A for about 10
seconds through the 30A output circuit breaker on my home brew 24V
battery charger.
Cleaning the battery connections is a good idea whether or not it
helps here.