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tonewheelkev 20th September 2010 09:52 PM

Arcam Alpha 8R Amp blowin fuses.......
Hi All:D

As it says....the 8R amp (Conf. with an 8P in Bi Amp mode!) is blowing fuses
....2 so far!!

Had a similar problem with a Mission Cyrus 1 recently, and cured it by replacing 4 X rectifier diodes in the hoping this might be a similar fix....?:mischiev:

I have a decent meter at hand....but have no idea how to test the O/P transistors....
What would members check first??:confused:


nigelwright7557 20th September 2010 10:46 PM

You need to check for a short from CE or DS on the output transistors.

Sometimes the driver is wiped out as well.

tonewheelkev 20th September 2010 11:03 PM

....Now then.....what is ....'the driver'...?

tonewheelkev 20th September 2010 11:31 PM

....testing MOSFETS......
With meter set for continuity...
....on LH both semi's show no shorting between pins

....on semi shorts between all 3 pins, and the other shorts between outer pins.....

Farnell lists several replacements for the IRF540....some with different specs:(


Browse for Products | Farnell United Kingdom

which one would suffice??? (I may as well replace all 4...??!)

richie00boy 20th September 2010 11:47 PM

Do you know what caused the amp to blow?

Avoid the IRF540N devices as they can't take the heat (literally). Use IRF540PBF or IRF540A. I do have some IRF540 made by ST for sale if you don't have enough to meet Farnell's minimum order.

tonewheelkev 21st September 2010 12:01 AM

Do I know what caused the amp to blow.....?
....MAY have inadvertently shorted o/p's while re-positioning speakers:(:(

(I know I should've turned off the amps before disconnecting and reconnecting)

.......I'll learn in the end.....

Of course....that could all be just couincidental......:confused:


richie00boy 21st September 2010 01:14 PM

Was music playing at the time?

tonewheelkev 21st September 2010 08:43 PM

...4 X IRF540PBF's (at 1.00 each from local Farnell)....and a 10p fuse later,
and all is well!!

Many thanks for your help....


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