Help with Peavey TNT 115 low output

[johnk_10]

OK...thanks. I didn't try the preamp out to another amp. When I plug into the preamp in, I do get output to the speaker, but it is low. I get nothing through the main input, so I suspect the poweramp. I will try what you suggest tonight, that should help for sure.
QUOTE]

actually, if you get nothing thru the main input, it sounds like it may be in the preamp. especially if you run the preamp out to another amp.

if you plug a bass into the power amp in, it should be very low since a bass doesn't have enough output to drive the power amp properly.

 

[Downlowd]

In defense of GreenBoy's post, it IS, unfortunately, very accurate. People will insist on opening a malfunctioning amplifier to "take a look" at what might be wrong without the slightest clue of the technical side. Resistors and other passive devices do not simply burn up for the sake of it or just to give you, the owner, a hard time. There has to be something wrong, most likely unseen, to cause the problem. I have had to repair more than a few units that the owner has attempted to fix (as have all techs), invariably the repair has cost much more than the original problem would have done.

Paul

Yes and the "original" problem was stated. The grommet on the power chord was gone. The previous owner continued to use it and the black and white 110v wires wore through and I'm sure shorted to the chassis. When I bought the amp the insulation was gone in places on the power chord. I bought a replacement chord and grommet and soldered them in. So the cause is fixed. So my original question was...given this problem what did it likely damage?

 

[hbarcat]

Yes and the "original" problem was stated. The grommet on the power chord was gone. The previous owner continued to use it and the black and white 110v wires wore through and I'm sure shorted to the chassis. When I bought the amp the insulation was gone in places on the power chord. I bought a replacement chord and grommet and soldered them in. So the cause is fixed. So my original question was...given this problem what did it likely damage?

That's a risky assumption that the faulty cord was the source (or the only source) of the problem and now that the cord is fixed you can repair what you assumed it shorted out and be good to go. It may or may not be true but you can't assume that it is. Still, it's no help in determining why the output is so low. The list of things that could have burned out is a lot longer than the list of things that couldn't.

Even though I've got some experience in electronics and in mechanical/electrical troubleshooting in general, I've had amps (including a Peavey TNT) that had some mysterious problem that needed to have the work done by an experienced amp technician because I knew that there is only so much I can do on my own.

The fact is, if it isn't something simple like a blown fuse, an obviously broken connection or an easily isolated part like a volume pot, then tracking down the problem will require an amp technician. You're hoping that someone will know exactly which component on your amp burned out based on the description you gave of the problem and will post some simple fix. I'd say the chances of that happening are slim to none.

The advice that was given about not mucking about with the amp if you aren't qualified is good advice and it isn't condescending. I follow it, myself.

 

[Rattman]

Hey again there Downlowd... I can see that you are getting kinda frustrated with any lack of clear direction with your 'low output' issue. I remembered just a couple of days ago that my very FIRST Peavey amp after about 25 years of flawless service did something similar to your TNT. I had no idea what it was, and normal troubleshooting brought me no closer to a solution.

I promply donoted it to a used music gear store for their disposal or repair. They gave it to a certified amp tech here in Orange County, Ca. The original voltage transformer had gone bad. It was replaced... the store immediately sold the amp to some local kid.

 

[Downlowd]

Hbarcat... thanks, I agree with you about the chord maybe not contributing to the problem but its a good place to start as everything else appears to be in good shape. With bare wires in direct contact with the chassis for who knows how long, I think it is reasonable to think that some damage occured, although I understand the problem may be totally unrelated. I bought it cheap because it was broken, I am in no hurry to fix it. I have a MB combo for gigs. I am just one of those guys that likes to fix stuff. I have had pretty good luck repairing amps so far.
Thanks Rattman, I suspect the transformer and will have some time tonight to check the voltages.

 

[Downlowd]

UPDATE

I got it fixed and man does it sound good. There was two problems with the amp. The first was the first voltage regulator on the amp circuit. There are two and one had voltage output and the other didn't. It was only $1.25 for a replacement. I soldered it in and the amp worked, but only when I plugged into the power amp in jack. Long story short, the power amp jack was bad. When you remove the 1/4 inch jack, the circuit stayed open and the signal path was interrupted. It was simple to bend the tab a bit to fix the jack.

So, I spent 20 bucks on a schematic and $1.25 for the regulator and the amp sounds alot better than I expected....that is usually the case with Peavey stuff though.

Thanks for tips, it certainly simplified things to determine that the preamp was working fine, but the amplifier circuit was the problem.