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Pioneer VSX 908 rds

 
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pravish



Joined: 13 Apr 2008
Posts: 2
Location: mauritius

PostPosted: Sun Apr 13, 2008 8:08 pm    Post subject: Pioneer VSX 908 rds Reply with quote

Hi everybody,I have this receiver :pioneer vsx 908 rds for a while but it has never been able to switch on properly.It remains on the stand by mode.Checked and found 2 FETs on the FL channel shorted.Replaced them accordingly but it doesn't obey so I 'triggered' the power through bypassing the "wake up" signal. Lo! the 2 Fets shorted again + 0.1 ohm going to the output channel.Wise to mention that the component was without any speakers conncted to it. Thanking you for all.
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pravish



Joined: 13 Apr 2008
Posts: 2
Location: mauritius

PostPosted: Mon Apr 14, 2008 3:26 pm    Post subject: Reply with quote

can anyone suggest me what ought to be the problem.Is it that the receiver was without load connected to it? Please help me. Thanks.
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vtech



Joined: 08 May 2006
Posts: 1214
Location: USA

PostPosted: Mon Apr 14, 2008 3:56 pm    Post subject: Reply with quote

From your description sounds like there is some sort of a driver/predriver problem prior to the final stage? In general if/when faced with a final stage failure, you must check any driver/predriver circuits that are used as controller or else it will destruct the outputs as soon as the power is applied.
Often it is best to use an isolation transformer(variac) to bring up the voltage slowly. This will provide a cushion to back down & save the outputs while allowing you to monitor gate voltages etc.

Not familiar with the specific unit but do you have any schematic or can you get one?

Sometimes, if you have a "good" channel, you can use it as reference point to do "spot checks" with an ohmeter (without any power applied). ----without further diagnosos, it is rather difficult to spot the cause.
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