electrical issue with radio installation

[doublechevy]

I decided to replace my original Magnadyne radio in my 2008 Knight 9900 series radio.

I decided to stay with Magnadyne as I read somewhere if you bought the radio directly fron Magnadyne they would make up the radio plug harness to meet installation requirements

I went with their M2 Multimedia model

They contacted me within a couple of days of placing order to find out what model coach and year the new radio was to be installed, they then provided the correct harness and plugs for my installation.

After installation ( fortunatley I left the radio out of the dash installation sleeve)
I started setting up the radio got a local radio station and proceeded to raise the volume of the radio, that is when the radio started shutting off and would start up again then do this continously until I lowered the volume it would stay on

I called Magnadyne customer support and was given to tech for troubleshooting the issue. first thing he wanted was to confirm the input voltage with a multimeter at the ground on the plug to the yellow wire which I did and, advised him that the voltage I measured was the same as the voltage on a digital voltage meter I had mounted into dash 13.2 V. ( radio was not on at that time) he then asked me to put a jumper wire between the Y & R on the radio plug I was doing that when I suddely lost power to my digital monitor on the dash and other 12V equipment

Told him I would call back when I cleared up the missing voltage

For some unknown reason the the solenoid for the 12v power in the coach had tripped, turned it back on with salesman switch

With everything back on including radio power I started checking voltages at the radio plug got about 12.0V radio would play until I raised the volume voltage would drop below 12V 11.8 - 11.7 found out that increasing volume increases power usage and with that increase the voltage drop was enough to affect radio ( on then off cycling) I suspected a bad ground, I located the chassis ground point, removed ground screw and wires cleaned them all replaced a couple of suspect terminals and reattached thinking I had surely cured the voltage drop issue. radio continued to cycle off on with volume up, ran a temporary ground from location in front run box Marked panel ground.
Radio functioned properly with volume turned up, will now install new ground wire directly to radio, Hope this will make all OK

[YC1]

This is a perfect example of how a digital voltmeter can trick you into thinking things are ok.

You are lucky in that the radio did not click off when first powered on. If it had been enough of a load to trip itself your digital voltmeter would not have been fast enough to catch it.

You did a great job chasing the ground issue. Since it is now working you probably have it back in the mount but to chase a bad ground, you must first find a good ground for your meters negative probe.

Then put the positive probe on the ground of the device in question. Any voltage showing up on the ground side is an indication of a bad ground.

The bad ground may have been there a long time and only showed up when the radio was hanging outside of the mount where you may not have had a grounded chassis due to not being in grounded mounting tray.

It is possible the antenna was not plugged in and it could be a source of a ground.

I have been caught by the digital voltmeter fooling me many times. Keeping an analog meter handy at all times I will watch the needle very closely. Any dip in the needle followed by the voltage going back up before turning on the device is an indication of a bad power source or ground as you have found.

Thanks for sharing this. I hope my response is clear and helpful to someone.

[doublechevy]

I have learned from your response not trust my readings with a digital meter
will dig out my analog meter and keep it handy

Thank you

Phil

[jacwjames]

Learn something new every day.



I have an analog meter, guess I'll have to keep it dusted off.

[153stars]

A incandescent 12v test lamp will do similar. A lowZ meter changes to low impedance there's usually a time limit for how long it can be tested at that setting Not sure if every lowZ meter works on DC. A solenoid/Wiggy meter will put a load a 120vAC line. I've seen the at garage sales for next to nothing.
I have had to deal with phantom induction voltage and voltages and circuits that can't carry a load. Even a 480v cartridge fuse that tested out on voltage scale and continuity but new 3phase compressor wouldn't start or blow the fuse out the rest of the way.
The old underground line to my garage did same thing on one line nearly 30yrs ago drove me crazy solid wire was probably cracked and burnt back, multimeter read 120v. I didn't know then what I do now.

[doublechevy]

I ended up running three new # 12 ground wires from from existing chassis grounding point.

Removed existing self tapping screw installed at factory for grounding and making a grounding stud , 1/4 stainless bolt, serated nuts, washers
cleaned frame at location of attachment covered all connections with DI-electric grease

1 ground dedicated to radio
1 ground dedicated to dash monitor, 12v socket, and 3 USB plugs mounted in dash
1 spare ground wire to under dash location

working fine so far