Rotel RMB-1075 and left surround not working....

[red71rum]

I have wanted a Rotel amp for some time and because my wife does not understand my home theater obsession, I bought one used from Craigslist. I had asked the only owner all kinds of questions and finally bought it. It came with a like new manual, untouched warranty card amd two T6.3 250V(I think that's what they were off the top of my head) still in plastic. The amp was in flawless condition aside from some dust. Anyway, I eagerly took it home used the bluejeans interconnects that he gave me, connected it to my Pioneer 1222-k preouts and tested it. I did a manual speaker level test, went through the different channels and nothing was heard from the left surround channel, I changed rca cables and still nothing. I knew the left surround worked on my receiver because that is what I had been using so there was nothing wrong with my cables. I did some research and opened up the Rotel after it had been powered down for an hour. Looking into the amp I found a fuse on the left hand side the fourth one closest toward the torrodial power supply was black. With much effort(I don't have tiny hands or at that time a fuse remover) removed the fuse and replaced it with one of the ones that came with the amp. I closed everything back up, connected everything turned it on and a "vvvvppppah" sound emanated from the amp, I smelled something electrical and I quickly shut it off. I removed the interconnects from the left and right surround and connected them back to my Pioneer. Now the Rotel just powers my L\C\R but my question is could I get the left surround working? I called Rotel and they sent me the fuse schematic and it turns out that I maybe should have also replaced the 3rd fuse, the one right next to the one I replaced. My question is it worth it to try again and replace both fuses. The other fuse looked fine to me, but maybe it was bad also?

[madmac]

I'm not an electrical expert but fuses blowing are usually a sign of something bigger wrong going on electrically. You have nothing to lose by replacing all the fuses.......but if fuses immediately blow again, there is a bigger problem going on.

[red71rum]

I'm not an electrical expert but fuses blowing are usually a sign of something bigger wrong going on electrically. You have nothing to lose by replacing all the fuses.......but if fuses immediately blow again, there is a bigger problem going on.

The former owner claimed it was working when he disconnected it two weeks ago. The only thing I did that might have caused a problem was that I had it connected to a power strip when it should have been connected directly to an outlet. I now have it connected directly.

Edit: What is the original power cord supposed to be like? This cord does not have a 3 prong end(a ground connection), but is only a two prong.

[srb]

The only thing I did that might have caused a problem was that I had it connected to a power strip when it should have been connected directly to an outlet. I now have it connected directly.

Connecting the amp to a power strip (or power conditioner) might restrict dynamics, etc. depending on the type of filtering and/or surge supression, but would not cause the amp to have a fault.

I don't know that having another bad (and unreplaced) fuse would cause the other fuse to blow, but if you replace the fuse(s) again, I would power it up without any interconnects or speaker cables and see if it blows under that condition; if not, one of the surround interconnects or speaker cables (more likely) may have since developed a short.

A low-cost multimeter is handy to have to check fuses as sometimes a fuse can be bad without it being blackened or seeing the filament separated (I once had a bad fuse whose filament had separated from the end cap with no visible sign of failure.)

But as previously mentioned, the blowing fuse is likely symptomatic of an internal component such as a transistor or resistor that has failed.

Edit: What is the original power cord supposed to be like? This cord does not have a 3 prong end (a ground connection), but is only a two prong.

If you look at the IEC AC power inlet on the amplifier, you will see that is only a two blade (ungrounded) receptacle, which explains the power cord having no ground pin, and even if you inserted a grounded three blade power cord, the ground wire would connect to nothing.

Steve

[madmac]

The former owner claimed it was working when he disconnected it two weeks ago. The only thing I did that might have caused a problem was that I had it connected to a power strip when it should have been connected directly to an outlet. I now have it connected directly.

Edit: What is the original power cord supposed to be like? This cord does not have a 3 prong end(a ground connection), but is only a two prong.

I have serious doubts that this unit uses only a two prong power cord ! It might not be the original OEM power cord. Check with Rotel on that one !

[srb]

I have serious doubts that this unit uses only a two prong power cord ! It might not be the original OEM power cord. Check with Rotel on that one !

[red71rum]

Connecting the amp to a power strip (or power conditioner) might restrict dynamics, etc. depending on the type of filtering and/or surge supression, but would not cause the amp to have a fault.

I don't know that having another bad (and unreplaced) fuse would cause the other fuse to blow, but if you replace the fuse(s) again, I would power it up without any interconnects or speaker cables and see if it blows under that condition; if not, one of the surround interconnects or speaker cables (more likely) may have since developed a short.

A low-cost multimeter is handy to have to check fuses as sometimes a fuse can be bad without it being blackened or seeing the filament separated (I once had a bad fuse whose filament had separated from the end cap with no visible sign of failure.)

But as previously mentioned, the blowing fuse is likely symptomatic of an internal component such as a transistor or resistor that has failed.



If you look at the IEC AC power inlet on the amplifier, you will see that is only a two blade (ungrounded) receptacle, which explains the power cord having no ground pin, and even if you inserted a grounded three blade power cord, the ground wire would connect to nothing.

Steve

Thanks Steve, I have it connected directly to the wall now. Last week I disconnected everything, took the amp apart replaced both Left surround fuses, blew out any dust bunnies etc. I then closed the amp reconnected it. I initially powered in the amp and nothing blew. I then connected the speakers and I heard nothing...from anything, turns out I had flipped the twelve volt switch. I flipped the switch, heard a vvvvspthtth sound, smelled electrical and quickly shut down the amp. Now when I connect the the surrounds to my receiver I have no problem. I am using the 1075 as an L/C/R amp I guess. The only thing it might be would be that the blue jeans interconnect is bad, but it looks fine to me from outside appearances? I am a sys admin/computer technician so I take stuff apart all the time but these fuses were tiny and hard to get to I can only work on this stuff on Saturdays when the kids are gone. I would rather pay someone as long as it was not prohibitively expensive. This amp even in its present state sounds so much better than my Pioneer, it really is amazing.