Arcam Alpha 5 prob - diyAudio
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Old 1st April 2007, 03:32 AM   #1
gman70 is offline gman70  Scotland
diyAudio Member
Join Date: Mar 2007
Default Arcam Alpha 5 prob

hello all. First post here. So al get an appology in just incase am in the wrong place.
I ahve a problem with my Arcam Alpha 5 Amp. out of the blue, it has ceased working.
I had a look inside and noticed that the 1 amp Timed/slow blow fuse had blown. I got replacement fuses and have since blown another 5. I have removed the circut board and there is no OBVIOUS sign of damage.
I cant afford to send it to arcam to be fixed. Has anyone got any ideas what the problem maybe and how to fix it? Any help welcomed as I miss my music.

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Old 1st April 2007, 06:53 AM   #2
big jim is offline big jim  England
diyAudio Member
Join Date: Feb 2006
Location: london
Hi its probaly the o/p transistors [fets]
i have the manual if you need it PM me

all the best jim
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Old 1st April 2007, 12:01 PM   #3
gman70 is offline gman70  Scotland
diyAudio Member
Join Date: Mar 2007
Hi Jim. Thanx for replying. Is the prob you suggested easily solved? Is it likely to be a pricey thing do you know?
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Old 1st April 2007, 01:16 PM   #4
diyAudio Member
Join Date: Apr 2004
I have an Arcam Alpha 7R here for repair at the moment

It is likely that the output MOSFETS on one or both channels (IRF540) have blown short circuit, causing a short across the power supply. IMO the heatsinks in the Alpha amps are far too small, so it's not really a surprise. There is also no TVS/MOV across the mains supply, so this amp seems to be suspect to power surges.

I would suggest that you just obtain new MOSFETS (IRF540N works, as should IRF540NPBF) and they are only about 2.50 each, BUT because you have tried so many fuses, it is likely that you have caused further damage to the circuit.

I also suggest obtaining the service manual from Arcam - they should send you this as a PDF file.
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Old 1st April 2007, 02:39 PM   #5
gman70 is offline gman70  Scotland
diyAudio Member
Join Date: Mar 2007
Thanks jaycee. I have contacted Arcam like you sed and will look to get these components you mentioned.
Are they readily available from the likes of Maplin or do I need a more speacialised supplier?
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Old 1st April 2007, 03:01 PM   #6
diyAudio Member
Join Date: Apr 2004
Rapid stock them, as do bigger suppliers like Farnell or RS. I would go with Rapid as they will cater for small orders - order code 47-0317. These days, I wouldn't touch Maplin with a barge pole.

If you want to confirm that the outputs are blown, unsolder them and use a continuity check or resistance check to measure between source and drain (pins 2 and 3). They are blown if they read short - you will probably find continuity between the gate and source/drain also.
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