Need some acvice

[Kevin99]

I have a Rotel RB985 power amp, wich I bought secondhand about a month ago. Was working fine till last night when the center channel protection light came on.
I switched off the amp and found it to be very hot. I checked all the cables and connections, and switched it on again, just to find that after about 2 minutes, all the protection light came on, and this time the amp was very very hot. I then removed it from the livingroom to my study and connected it to a Denon reciever with pre-outs and tested all the channels two by two in stereo mode and all was working fine with nothing heating up at all. I did not play the amp very loud in the livingroom asswell and their is plenty of spacfe around the amp. This morning I borrowed another amp from a friend and tested it with my processor and it was working fine.
I also opened the cover of the 985 and had a look inside, with no visible damage at all.

My question is what could be wrong with it, and even more importent, what will it cost to fix the damned thing.
Any help would be much appreciated.

Regards

[Kevin D]

So it worked fine in the study on the Denon. Have you moved it back into living room and tried it again? Sounds like you may have had a stray piece of speaker wire touching the case that you didn't have in the study or on the borrowed amp.

The amp warmed up trying to drive a partial dead short, then went into protection mode. Once hot, it's easy for the entire amp to go into protection.

Kevin D.

[PewterTA]

One thing that kills amps or anything electronic is dust. Since it conducts electricity you have to be care with how much dust gets in to an amp/pc/etc. It could be that something like that has caused an issue inside and you won't notice it, but it effects the amp and could've been building up from the person you got it from.

I always take all my electronics apart and blow them out at least once a year. So far, I have not had anything fail me. (goes looking for wood to knock on too).

It could be a bunch of things from a small resistor to a capacitor to anything on there that could be causing a problem. Especially if the amp will trip with nothing attached to it. I'd plug it in and leave it on with nothing attached and see if it ever trips...or it might take a load to have it do the same thing.

If you lived by me I could test all the components and get whatever it is that needs fixed for you. But any Rotel dealer should be able to get it fixed for you.

[Kevin99]

Thanks guys.
I did try the amp again today and still same, after about a minute it started to get very hot, so I tried it with the processors zone 2 outputs in my study. And played for most of the day on various stereo combinations without any overheating whatsoever.

I made 100% sure that al the connections were perfect this morning before I connected all the channels to the processor.

I heard from an friend that it might be crosstalk between the channels??? Whatever that might be.

[GregLett]

So it worked fine in the study on the Denon. Have you moved it back into living room and tried it again? Sounds like you may have had a stray piece of speaker wire touching the case that you didn't have in the study or on the borrowed amp.

The amp warmed up trying to drive a partial dead short, then went into protection mode. Once hot, it's easy for the entire amp to go into protection.

Kevin D.

Kevin99,

It does sound like you may have a stray wire touching. It might not be at the amp end but at the speaker end. You could have a damaged speaker cable.

How about disconnecting all the cables and connecting back one channel at a time. Each time you connect a channel play the amp for the 2- 3 min period to see if the problem. You should be able to isolate the problem that way.

[Kevin99]

Kevin99,

It does sound like you may have a stray wire touching. It might not be at the amp end but at the speaker end. You could have a damaged speaker cable.

How about disconnecting all the cables and connecting back one channel at a time. Each time you connect a channel play the amp for the 2- 3 min period to see if the problem. You should be able to isolate the problem that way.

But why does this not happen with the power amp that I have borrowed from a friend?
It is playing fine at the moment.

My setup also consist of :RSP1068, B&W 683, B&W HTM61, B&W sub and monitor audio bi/di-poles.

I am affraid that if I move it back again, that I risk serious damage to the amp.

[GregLett]

But why does this not happen with the power amp that I have borrowed from a friend?
It is playing fine at the moment.

My setup also consist of :RSP1068, B&W 683, B&W HTM61, B&W sub and monitor audio bi/di-poles.

I am affraid that if I move it back again, that I risk serious damage to the amp.

Right, I see that now.

With the amp not displaying the same symptom in your study setup
you might send it in for repair, and they will say there is nothing wrong.

Your best bet may still be the slow re-connection of wires to see which connection causes the problem.

But if you are worried, just send it in and hope they do find something.

[Kevin99]

Right, I see that now.

With the amp not displaying the same symptom in your study setup
you might send it in for repair, and they will say there is nothing wrong.

Your best bet may still be the slow re-connection of wires to see which connection causes the problem.

But if you are worried, just send it in and hope they do find something.

I will try it tonight, thanks for all the help.

[Kevin99]

OK now I do not know anymore. After losts of Sh*t moving speakers around, I had the amp playing 100% in my study on all 5 channels at the same time through the zone 2 of the reciever using Y-splitters for about an hour. Bought new speaker cable for the rears and went at it again in the living room. Connected the center and fronts and everything was fine, but when I connected the one rear, it started to warm-up, disconected that one and connected the other one and same thing happened, and fairly quickly, within half a minute the amp was starting to get very warm at very low sound level. Disconnected and connected my friends amp again and no problem????

Should I just take the amp to the agents, but why was it playing all 5 channels with no problems through the zone 2 of the reciever?

[PewterTA]

Did you try connecting your mains to the surround posts to see if the amp heats up that way?! You need to try to figure out if it's only those posts that cause the problem or not. Heck even hook up the center to one of those and see if it heats up... If it does then you know it's those connections that you are having problems with. Which could be something wrong with one of those circuit boards.

[GregLett]

OK now I do not know anymore. After losts of Sh*t moving speakers around, I had the amp playing 100% in my study on all 5 channels at the same time through the zone 2 of the reciever using Y-splitters for about an hour. Bought new speaker cable for the rears and went at it again in the living room. Connected the center and fronts and everything was fine, but when I connected the one rear, it started to warm-up, disconected that one and connected the other one and same thing happened, and fairly quickly, within half a minute the amp was starting to get very warm at very low sound level. Disconnected and connected my friends amp again and no problem????

Should I just take the amp to the agents, but why was it playing all 5 channels with no problems through the zone 2 of the reciever?

Kevin is everything the same cable wise with the surrounds? were you using the same cables and speakers in the study?
If the combination of channels were the problem the problem should have showed in the study. The only thing I can think of is that you have some sort of low impedance short on the cables in the main system.

[Kevin99]

Kevin is everything the same cable wise with the surrounds? were you using the same cables and speakers in the study?
If the combination of channels were the problem the problem should have showed in the study. The only thing I can think of is that you have some sort of low impedance short on the cables in the main system.

Different speakers were used in the study, but the cales are brand new Monster cables that I bought yesterday. I will try again tonight with different speakers for the rears and se what happens, but the Monitor Audio BR-FX are brand new.

[GregLett]

Different speakers were used in the study, but the cales are brand new Monster cables that I bought yesterday. I will try again tonight with different speakers for the rears and se what happens, but the Monitor Audio BR-FX are brand new.

Kevin,

Any Luck?

[Kevin99]

Last night I spend about 5 hours with the setup and came to only one conclusion and this is what is causing the problem. I hooked up everything in the living room, but too the rear speakers from the wall and connected them with shorter speaker cable, as I wanted to try my pair of speakers in the study as well if the problem persisted. And no heat, nothing wrong, 100% working. I then took the origanal cable (10 meter monster home series) and connected it up again and it started to heat up again. So if I run the system with 3 meter cable to my rear speaker, no problem, but with the 10 meter cable, it heats up. The monster cable is brand new, not even a week old and the problem also arise with my previous 10 meter cables.
What would cause this to happen, as I have no clue?

[GregLett]

Last night I spend about 5 hours with the setup and came to only one conclusion and this is what is causing the problem. I hooked up everything in the living room, but too the rear speakers from the wall and connected them with shorter speaker cable, as I wanted to try my pair of speakers in the study as well if the problem persisted. And no heat, nothing wrong, 100% working. I then took the origanal cable (10 meter monster home series) and connected it up again and it started to heat up again. So if I run the system with 3 meter cable to my rear speaker, no problem, but with the 10 meter cable, it heats up. The monster cable is brand new, not even a week old and the problem also arise with my previous 10 meter cables.
What would cause this to happen, as I have no clue?

What gauge is the wire? It sounds like there is too much resistance in the cable. If the cable is small in diameter (20, 22 gauge) + is very long that would present too much of a load for the amp. It seems you may need thicker wire (10 or 12) gauge wire for the long run.

At lease you found the problem now though :T

[Kevin99]

What gauge is the wire? It sounds like there is too much resistance in the cable. If the cable is small in diameter (20, 22 gauge) + is very long that would present too much of a load for the amp. It seems you may need thicker wire (10 or 12) gauge wire for the long run.

At lease you found the problem now though :T

The cable is 16 gauge.

[GregLett]

I never use smaller than 14. I would pick up some cheap 10 or 12 gauge to try.
I would recommend 10 though less work for the amp.

[Kevin99]

I never use smaller than 14. I would pick up some cheap 10 or 12 gauge to try.
I would recommend 10 though less work for the amp.

I took it to the Rotel agents here in South Africa. They said about a week.
I do not hope it is something big, with the exchange rate as it is at the moment, have seen our currency been cut in half the past 2 weeks.

[hifiguymi]

You shouldn't have a problem with 16ga wire at that length. Greg is correct that a larger one would be better but there must be something else wrong with that wire or its installation. Did I understand correctly that the wire running in the wall? If so, there may be a problem there like a staple or nail through the wire.

Eric

[Kevin99]

You shouldn't have a problem with 16ga wire at that length. Greg is correct that a larger one would be better but there must be something else wrong with that wire or its installation. Did I understand correctly that the wire running in the wall? If so, there may be a problem there like a staple or nail through the wire.

Eric

No, the wires are not in the walls and I did replace the wires and rechecked all connections. But the setup is working fine at the moment with a amp that I borrowed from a friend until I get mine back.

[GregLett]

The cable is 16 gauge.

It is strange that the amp is so sensative to the cable length something must be a little off with it.

[Kevin99]

Just called the agents and they are busy testing the amp to see that everything is working fine now. Repair cost - $50.
:T

But he could not tell me what was wrong, will get back to me later today.