Electricals Again (Radio)

[mkb]

STOP THE PRESSES...

Here the latest update....

Grant said...

>>>>>>>>>>>>>>>>>>>>
These radios have two powered inputs - one that is always on, and one that is 
switched.

Some power is always present to maintain memory, etc.

When you turn the knob, or push the button, or whatever you do to turn it on, 
one of two things happens_

1. a switch on the knob shaft connects the full power to the amp/etc.
2. a relay closes and does the same (remember, there is supervisory power to run 


a relay)
<<<<<<<<<<<<<<<<<<
Beginning to make sense and totally agree.

>>>>>>>>>>
I would guess the on/off/vol switch, or the relay, is kaput.  Buy a new one or 
have it repaired (probably cheaper to get a new/rebuilt one). Search the web, 
including ECS tuning, force 5 ( a lister i believe)
<<<<<<<<<<<
Relay?  I don't see one in the circuit diagram, and as I mentioned, the radio 
was changed and the problem re-appeared soon after.

>>>>>>>>>>>>>>>>>>
If you want to check your wiring further, measure from a solid ground to the 
input to the fuse. Measuring "across the fuse" brings into question what 
potential the unpowered side is at. Is there a capacitor there with residual 
charge? Maybe.  Who knows. Dont measure there. Measure to a known ground 
potential.

Grant
<<<<<<<<<<<<<<<<<<<<
Yes, I want to check my wiring further, so this is what I did all day today - 
dashing from the garage and the TV to catch as much football as I could....

OK, so I was able to locate a ground close to the fuse panel on the left hand 
side of the vehicle.  I pull the fuse to measure voltage between the fuse panel 
terminals and ground.

Ignition Switch Off
------------------------
So when I measure from the input (red wire +30) to the ground I get about 
12.5V.  If I measure from the other terminal in the fuse i.e. the red/blue wire 
(going out I assume) to the ground point, I get about 1.6V.

Ignition Switch Half Way On (Sorry, don't know how else to describe it)
-------------------------------------------------------------------------------------------

Measure from red wire (+30) to ground, 12.5V.  Measure from red/blue wire to 
ground 1.5, 1.4, 1.3V... and dropping...(remember, the fuse is pulled), but why 
is the voltage dropping???

Ignition Switch On
------------------------
Measure from red wire (+30) to ground, 14V.  Measure from red/blue wire to 
ground 1.2, 1.1V... and dropping (fuse still pulled).  Voltage still dropping, 
why??

Turn Everything Off
-------------------------
Measure from red wire (+30) to ground, 12.5V.  Measure from red/blue wire to 
ground 1.0, 0.9V... and dropping...and fuse still pulled.

20 Minutes or so Later
-----------------------------
Measure from red wire (+30) to ground, 12.5V.  Measure from red/blue  wire to 
ground 22mV and fuse still pulled.  Voltage almost zero.  Strange!

If I pop the fuse back in and pull it again, I get 12.5V from red (+30) and 1.6V 
from red/blue.  If I pop the fuse back in, come back in 20 or minutes, I get 
12.5V from red (+30) but only around 22mV from red/blue.  This leads me to 
believe that this is not sufficient voltage to maintain radio state.  I think 
this indicates that I have a short to ground, right?  Or do I have a bad relay 
or capacitor?  Or all three?  


Well, I think I'm going to have to pull the radio at this point and check the 
connections in the wiring harnesses.  According to the circuit diagram, I also 
have a  ground connection for the red/blue wire in the luggage compartment.  Do 
I need to check this?  ('cause it looks like a pain to pull all the rear 
interior trim).

Thanks for listening.

--
mohammed
99 a6 2.8q avant
97 1.8qta