Converter question

We bought a 1988 Prowler 22h travel trailer a couple of weeks ago. I've been going thru and trying to make sure everything is mechanically sound before our first trip with it in a couple of weeks. The battery that was in it was dated 2008. I hooked my battery charger up to it and it was dead. While the charger was on I noticed my 12 volt lights worked and my control panel showed the appropriate lights when I would hit the battery button the lights would light up....same with the water tank lights, holding tanks, etc. I replaced the battery with a new deep cycle marine/rv battery and since then nothing works off the battery. No lights, recepticals, the control panel is dead. When I plug in everything works great....all lights,plug ins, AC, water pump, control panel indicator lights work....everything.
I have a 30 amp fuse coming off the battery....replaced the fuse and I have power behind the fuse so I know it is good. The converter in the trailer is a Magnatek TU-740-2....I'm wondering if the converter is shot. It's got a hum to it when I'm plugged in. I'm not missing a fuse somewhere that would cause this? Its weird that it worked with the old dead battery but not with the new fully charged battery.
Any help/advice on where to look next would be greatly appreciated.

Disconnect the negative cable from the battery. Then while plugged into shore power, check the voltage on the negative and positive cable. It should be reading somewhere around 13.5 volts. If it does, then your converter should be good.
Whereas some of your stuff is working when plugged into shore power leads me to think the converter is OK but it's good to check it anyway.

When I plug in everything works great....all lights,plug ins, AC, water pump, control panel indicator lights work....everything.

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[font=verdana, arial, helvetica, sans-serif] This says the converter is working as it should.  Better take another look at your battery installation.  [/font]

a 2008 Battery SHOULD Be dead.. A magnetek converter SHOULD be upgraded. Though if your battery is 10 years old.. It might be a decent one.

But a 10 year old battery .. Average life is 7-10 years.

As others have observed, the converter is working because it is providing 12v power when you plug in.  Apparently you have a problem with the battery connection. If not at the battery end, maybe where it connects to the 12v power distribution panel.

However, it would be a good idea to replace that old Magnetek anyway. The technology is old and very hard on batteries if connected to power for more than a day or two at a time. A new converter/charger will give superior charging and much longer battery life.

Molaker said:

[font=verdana, arial, helvetica, sans-serif] This says the converter is working as it should.  Better take another look at your battery installation.  [/font]

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Am I thinking wrong that the only thing my converter does while plugged into shore power is to charge my battery....it shouldn't have any effect on everything else working?
when I'm not plugged into shore power that's when my converter....converts the 12v battery power to 120v and that's what should let me turn on a few lights, and check things out on my control panel ( battery level, tank levels).
Should my gas detection monitor be working on battery power.....it works when I'm plugged into shore power but not on battery power.....Another reason I'm thinking the converter isn't doing its job.

thanks for the replies!

Sounds to me like a battery disconnect switch somewhere.
Also check to see if you have power on BOTH sides of fuse. Could be the fuse holder.
If you have 12VDC when plugged into shore power then the converter is certainly working.
Yes ....your wrong on the converter. It charges battery and provides 12VDC for the coach. It does not create 120V. It changes the 120VAC, which is what you plugged into, to 12VDC which is the coach power.
An inverter is the device which converts 12VDC into 120VAC. This allows AC devices such as tv's, coffee pots, mixers, microwaves and the like to be used when shore power (plug in at RV site or home) is not available.
This is known as boondocking. Basically off grid, like camping in the desert of forest.

Koodog said:

Sounds to me like a battery disconnect switch somewhere.
Also check to see if you have power on BOTH sides of fuse. Could be the fuse holder.
If you have 12VDC when plugged into shore power then the converter is certainly working.
Yes ....your wrong on the converter. It charges battery and provides 12VDC for the coach. It does not create 120V. It changes the 120VAC, which is what you plugged into, to 12VDC which is the coach power.
An inverter is the device which converts 12VDC into 120VAC. This allows AC devices such as tv's, coffee pots, mixers, microwaves and the like to be used when shore power (plug in at RV site or home) is not available.
This is known as boondocking. Basically off grid, like camping in the desert of forest.

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I do have power on both sides of the 30A fuse coming off my battery box. with the fuse out... I have power to one side.....with the fuse in, I have power farther down the line.
I also wondered about a battery disconnect switch since it worked with the old dead battery w/ a battery charger on.....but the minute I put the new battery in it didn't work. where are battery disconnect switches normally located.....been thru everything and haven't come across it yet.

Am I thinking wrong that the only thing my converter does while plugged into shore power is to charge my battery....it shouldn't have any effect on everything else working?

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As koodog explained, the converter/charger is active only when plugged to shore power and its job is to produce 12vdc from 120vac shore power. It both charges the battery and substitutes for it as the 12v power source.

The device that converts battery power to 120vac is called an inverter and your rig doesn't have one unless it was an aftermarket add-on.  That would be a rare upgrade for an older Prowler like yours, mostly because it lacks enough battery capacity to make an inverter useful.  When you are not plugged to shore power, you do not have any 120v power unless you also have an inverter and plenty of battery capacity.

when I'm not plugged into shore power that's when my converter....converts the 12v battery power to 120v and that's what should let me turn on a few lights, and check things out on my control panel ( battery level, tank levels).

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Ummm... Nope, that is called a CONverter. You built-in lights and control panel are all 12V. IF you have an INVerter it would be to power only the entertainment centre in most cases. A CONverter uses 120V from being plugged in to charge the batteries and help run all the 12V stuff. When equipped, an INVerter uses 12V from the batteries to produce 120V AC for things like the TV when NOT plugged in.

D B said:

Am I thinking wrong that the only thing my converter does while plugged into shore power is to charge my battery....it shouldn't have any effect on everything else working?

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The Converter converts 120 VAC or there abouts to 13.6 Or 14.6 Or 15.6 (Depending on the operating mode) volts DC. 13.6 is a 12 volt battery on float (14.6 is charging bulk/absorption and 15.6 Equlazition for MOST Lead Acid batteries. ALL voltages are "Approximate" and the precise voltage depends on the specifics of the battery.. But those figures are good enough for this post)

Absent the battery it produces 13.6 VDC to power everything that runs off batteries. 
For me that includes all the lights (interior) the Fridge (Control power) Water heater (Control power) FURNACE, Air Conditioner (Control power) water pump, Slides, and I'm not sure what else. but all the "Battery operated" stuff.  Oh and a Kenwood TS-2000 (100 watt Ham Transmitter/Receiver) that puppy is the major DC sucker in the house other than the furnace. (about 20 amps peak).