Arcam Alpha 8R problem

[goodlife]

Model:
Arcam Alpha 8R amplifier

Problem:
when i turn the amplifier on the amber standby (mute) light does not go off. The volume knob turns when the remote is used but does not go off mute. No sound comes out of the speakers. Obviously the protect circuit has kicked in.

I have removed the link which connects both amplifier channels to the protection circuit (VI_PROTECT link LK1085), to see if I could find out which channel is causing the protection circiut to kick in. However now the amplifier works; sound from both speakers, tone controls, volume, remote, mute all work.

Just for reference one channel has a speaker output dc voltage of 23mV and the other 15mV.


Questions:
I thought protection would only start if the amplifier had generated a fault which would stop it working, whereas mine appears to work fine. Am I completely wrong on this?

Does anyone have any ideas why the protection has started even though the amplifier appears to work with protection disabled?

Is it safe to run the amplifier with this protection disabled?

Kind Regards
Goodlife

 

[jaycee]

The VI protect circuit kicks in if it detects too much current flowing through the MOSFETS. Does any channel get very hot at idle?

If you contact Arcam they will send you the service manual for this amp as a PDF, which is nice

I would check any resistor in the VI protect circuit marked as "FU" (fusible) first. It's possible one of them decided to open.

Your amp will be fine without the VI protect provided you don't abuse it by playing it excessively loud for long periods.

 

[goodlife]

thanks for the reply.

Both channels are cold at idle. I think I'll follow your advice regarding fusible resistors. I'm begining to think that it is probably a fault in the current detection circuit on one of the channels as nothing gets hot during full operation at a reasonable volume. Thanks to the good people at Arcam I have a copy of the service maunal to assist in my fault finding.

I'll post anything new I find

Kind Regards
Goodlife

 

[MisterEcho]

Hello, reviving an old thread here but thought it was worthwhile.


I had a similar problem with an ALPHA 9 integrated amp after water got spilled through the vent on the top killing the right hand channel MOSFETs. Replaced the 4 MOSFETs but the Protection / Standby - Orange LED (LEDERR) wouldnt go out. Amplifier was working flawlessly with the protection relays activating as per originally designed but the protection LED stayed lit. More annoying than anything else but also a bit concerning connecting it to a pair of 15" Tannoy monitor golds just on the chance something was wrong.


After many hours of fault finding/ Checking components/ Desoldering/ Test Point voltages/ Etc..... what was causing the problem was something very simple.....


When the water took out the MOSFETs somehow the system went into some form of latched mute "protection" via im assuming the PIC16 microcontroller although MUTE wasnt enabled and sound was flowing from the speakers. To solve the problem I had an epiphany after many hours and grabbed the remote.


I simply pressed the mute button whilst it was on then pressed it again. Voila problem solved!!!


Thought it might be helpful