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Old 28th March 2007, 07:55 PM   #1
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Default Rotel rb970bx mk11 dead

I use two of the above power amps in bridged mono mode on my hi fi system, one recently refused to power up, on first inspection the two fuses rated at 8A had blown, I substitued the ones from my other amp and they blew straight away(under no load), the fuses are located next to a large torriodal transformer,has anyone any helpful pointers to fix my amp?.Thanks
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Old 28th March 2007, 08:20 PM   #2
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Are you familar with a DMM and electronic component identification and testing?


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Old 29th March 2007, 06:46 AM   #3
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I can use a DMM and an AMM, I can recognise most ic components and would appreciate some help (if DDM & AMM are not digital /analogue multimeters I may be on the wrong forum)
Thanks Dave and his very nice wife Julia.
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Old 29th March 2007, 01:15 PM   #4
jaycee is offline jaycee  United Kingdom
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It's most likely that the amp didn't like whatever load you were using while bridged, and the output transistors have blown.

They will be the devices attached to a large heatsink. Test these for shorts between collector-emitter. There may well be further damage other than these, and without knowlege of amplifier circuits and how they work it'll be tricky to repair - you may well just make things worse.
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Old 29th March 2007, 01:17 PM   #5
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scooter
Who In the hell is julia??
Ok so your instantlly blowing fuses.We need to locate the dead short.Unplug the unit from the mains power and remove the case. Look things over for obvious problems (burnt components etc.).If you have a schematic or a service manual that would be a big help. But the next best thing in a working second amp you can use it for referance.Look and see if you have more than one fuse inside the case. Does the rotel have BJT,FET's or chipamp output devices?




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Old 29th March 2007, 02:13 PM   #6
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scooter
According to Jaycee I guess it has BJT devices.I concur with his statements.

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Old 29th March 2007, 06:16 PM   #7
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Using my good one as a reference and your helpful advice, I have got a definate problem on my right channel,thank you. I am going to attempt to fix it. Thanks
Julia is my wife,
Scooter
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Old 29th March 2007, 06:38 PM   #8
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OK.I take it,your name is Dave also.LOL Glad we got that cleared up.







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Old 30th March 2007, 01:06 AM   #9
jaycee is offline jaycee  United Kingdom
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I have schematics for a few Rotel amps (not that one, unfortunately) and they always seem to use a fully discrete topology.

scooter, what power BJT's are used in the unit? If they are shorted, you may have to replace the driver transistors also. If you're lucky (and both transistors died) everything else should be OK. You will need to adjust the bias on the channel that's had parts replaced though.
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