Film-Tech Forum ARCHIVE: Faulty Crown MT

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Posted by Antonio Marcheselli (Member # 373) on 01-20-2002, 05:42 AM:

Hi,

I have a Crown MT 2401 that has some problem. It seems that, in stereo mode, the on/off protection of channel 2 is not working.
I've connected a 2$ speaker to channel 1 and I hear a "tic" after few seconds I turned off the amplifier and nothing when I turn it off (just another tic). Normal.
On Channel 2 The speaker move itself in the exact moment I turn on the amplifiers and I hear a LOUD "TOC" when i turn off the amplifier.
I had the speaker backside on a table: it jumped in the air.

In Bridge mono mode, the protection system works properly. I will use the ampli in mono bridge, but is there anything that I can check/do for stereo mode?

Bye
Antonio

Posted by Josh Jones (Member # 447) on 01-20-2002, 12:52 PM:

It sounds as if your channel 2 died. does it still amplify, if you feed audio into channel 2 can you hear it on the speaker. Is it distorted, noisey, fuzzy? it sounds as if one half of the amplifer has died. if it is causing the cone to pull inward. the bias could be off as well, but it sounds as if the positive rail (the part of the amplifier responceable for pushing the cone out) has failed. there are a lot of guys on this site that know a lot more about these amplifers than I do. I'm no expert, but I would suggest having it take to the shop for repairs.

Josh

Posted by Antonio Marcheselli (Member # 373) on 01-20-2002, 02:55 PM:

Josh,

Thanks for your help.

No, i didn't tried to amplify something with channel 2. I will do it and I'll let you know.
That amplifier worked in parallel/bridged mode for 6 years as Subwoofer amplifier.
Cannot just the on/off protection of channel 2 gone?

Bye
Antonio

Posted by Paul G. Thompson (Member # 655) on 01-20-2002, 05:35 PM:

I think you lost an output transistor or two. I would recommend following Josh's advice, and send it in for repair.

When I was a tech for MTS, our experience was to send the unit back to the manufacturer or an authorized service center for repair.

If memory serves me correctly, I think those have Darlington output transistors, and if so, it can be a real nightmare to deal with unless you have fully equipped repair facility with expert technicians.

Paul

Posted by Antonio Marcheselli (Member # 373) on 01-21-2002, 04:21 AM:

Paul,

The problem is that I had that ampli for free and I would like to use it to amplify a subwoofer in my future home theater room. If the amply has to be repaired, I believe that it would better to buy another one, a better one (also, it has too much power for me!).
I'll write to Crown, asking for opinions...

Bye
A

Posted by Antonio Marcheselli (Member # 373) on 01-25-2002, 12:28 PM:

So, I've tested the ampli.

I've connected the speakers after I turned on the ampli, so I didn't broke my two speakers!!

Both channel of the amplifier are working properly.

I suppose that it is just a "bump protection" fault.

Anyone has an idea of how to proceed?

Bye
Antonio