Hum in the Cassette/Radio

Hi everyone!  Just installed an "in-dash" style Cassette/Radio in our TM and it hums when the TM 110 volt plug is connected to main power.  When I disconnect the plug and run off of the TM 12volt battery the hum goes away.  I've tried the white ground wire in the stereo wire bundle inside the mounting hole (above the fridge), the ground of the 110volt plug beside the fridge and have also tried connecting the stereo ground wire to a spot under the TM on the steel frame to no avail.

On a  separate (but related) note...how have you removed the speaker grilles?  I attempted to remove them but stopped when I felt I needed to get my allignment tools (hammer and a flat bladed screwdriver) out of the toolkit.
Any suggestions would be appreciated.
Thanks!
Mark

Try a line filter in between the power source, and the radio, this is a frequent problem in cars, and that's how it's usually solved. Another thing to check is how close your non sheilded 12v lines are to the non sheilded 120V lines. I mearly mention that because I know the problems that can be had if you use a plain old phone line for a modem and bundle it in with also unshielded 120V power lines. There is a lot of line noise, and slow connects and downloads. Hope this helps!


[glow=red,2,300]Happytrails.......[/glow]

Might try Radio Shack for the inline filter.

ColoradoCop

Thanks for the replies!  Will give the filters a shot when I get home.
Mark

Mary and Mark,

Does the Hum occur when a cassette is played ?
Or the AM Radio ?
Or the FM Radio ?
Or everything ?

Sounds like you are picking up 60 HZ from the AC Power

Need a little more info to help with diagnosis

DR. John

The hum is present when the unit is powered on irregardless of mode or volume setting...ie even when the volume is on zero.

Mary & Mark,

My guess is the hum is being generated by the TM converter.

I would try wiring the radio directly to the TM battery & see if this removes the hum.

Dan

The radio should be power by one of the accessory circuits not a "12v" circuit used by the appliances.  On my converter there are about 6 or so separately fused 12v circuits and the last three are the accessory circuits.

The 12v circuits are disconnected from the battery when plugged in to AC and are powered by a full wave rectified AC current.  This is not filtered.  The accessory circuits always have the battery in the circuit to filter out the AC hum.  You can find the accessory power at your cigarette lighter plug since this is close to your stereo.  It should be fused with a 15 amp circuit.

I have the accessory circuit "#1 Radio" connected and verified by disconnecting the fuse and power goes off on the radio.  Installed  a 10 amp "Heavy-Duty Automotive Electrical Noise Filter #270-0518 Radio Shack".  The hum persists.  Next I will try a direct connection to the +12 v terminal on the battery.  If that fails...back to a walkman.

Interesting...

Putting on the EE cap, three things I would check next:

1) Is the converter OK?  Since I'm certain you can't put a scope on it, at least check it for DC voltage.  You should find about 13.5v [the battery charge voltage when plugged in] on the accessory circuits and about 12.6 volts on the other 12v circuits.  You might see two big button diodes on an aluminum plate inside the converter.  It could be that one of these fails but checking this requires some expertise.  If all your appliances work well and the battery charges up fine then I would tend to discount this.

2) Ground loop carrying current or an appliance causing interference?
I think you've checked this already.  Shut off the AC breakers one by one, even the main one, and see what happens.  Also, pull each DC fuse one by one.  

2) Is the RFI emitted or conducted?  If the hum persists using a separated power supply to the radio, the interference mightbe through the antenna.  Usually though a 60Hz hum is a [conducted] power supply issue.

3) Check the routing of the speaker wires.  Although unlikely although it is possible that the speaker wires could be closely coupled enough to pick up.  Such a hum source would be also present with the stereo off.