I just bought an Arcam Alpha (original model - 1984) as a working amplifier, and after 1 hours use the fuse blew.
(I know that there is a similar thread on the BB, but I think that this is a different problem).
I found that it had a 7.5A 250V fuse in the PSU fuse FS201.
If I fit a 500mA fuse in, which I think is the correct one, the amplifier starts, but fails in seconds.
While I've had the amplifier working, I've checked the output of the secondaries with an AVO meter, and it appears that the output is approx 25V each coil.
With the device turned off, I went around with an ohm meter, on the transformer, and there is low impedance (not 0) on the primary coil, low impedance on the secondaries (not 0), and nothing showing between the primary and secondary coils.
From what I've described above, I think that it's likely that the transformer may be okay?
I've emailed Arcam for a schematic yesterday, which I hope arrives soon, but in the meantime has anyone any suggestions on how to progress with diagnosing the faults, short of replacing things until I run out of patience, money, or it's fixed!
Best wishes,
Twosheds.
(I know that there is a similar thread on the BB, but I think that this is a different problem).
I found that it had a 7.5A 250V fuse in the PSU fuse FS201.
If I fit a 500mA fuse in, which I think is the correct one, the amplifier starts, but fails in seconds.
While I've had the amplifier working, I've checked the output of the secondaries with an AVO meter, and it appears that the output is approx 25V each coil.
With the device turned off, I went around with an ohm meter, on the transformer, and there is low impedance (not 0) on the primary coil, low impedance on the secondaries (not 0), and nothing showing between the primary and secondary coils.
From what I've described above, I think that it's likely that the transformer may be okay?
I've emailed Arcam for a schematic yesterday, which I hope arrives soon, but in the meantime has anyone any suggestions on how to progress with diagnosing the faults, short of replacing things until I run out of patience, money, or it's fixed!
Best wishes,
Twosheds.
The 7.5A fuse is *definitely* wrong ! and you are correct it should be a T500mA fuse.
If Arcam don't get back to you, I have the service manual for the early Alpha's here.
Might be worth checking C212 in case it's gone short (it's an X-rated capacitor across the Live and Neutral terminals). Try powering up with the secondaries disconnected from the PCB. If the fuse still blows then that capacitor is probably bad (it'll have seen a lot of abuse!)
If Arcam don't get back to you, I have the service manual for the early Alpha's here.
Might be worth checking C212 in case it's gone short (it's an X-rated capacitor across the Live and Neutral terminals). Try powering up with the secondaries disconnected from the PCB. If the fuse still blows then that capacitor is probably bad (it'll have seen a lot of abuse!)
Thanks for the replies, and the tip. I think that I'll replace that capacitor before removing the secondaries from the circuit, as this looks the easiest thing to do, and cost from Farnell is only 20p to boot.
This is a suppression capacitor isn't it? Excuse my lack of knowledge, but does this suppress the amplifier from creating interferance with other devices? Would it be safe to run the amplifier for test purposes without this capacitor do you think?
(I have not heard from Arcam yet.)
Thanks again,
Paul.
This is a suppression capacitor isn't it? Excuse my lack of knowledge, but does this suppress the amplifier from creating interferance with other devices? Would it be safe to run the amplifier for test purposes without this capacitor do you think?
(I have not heard from Arcam yet.)
Thanks again,
Paul.
You mean this one http://www.diyaudio.com/forums/showthread.php?s=&threadid=121748We got there in the end.
disconnect the transformer from the downstream side as suggested.
Then plug in a mains bulb tester. power up the transformer through the mains bulb tester.
Tell us what you measure/find.
The X rated capacitor on the primary side is to suppress interference coming in from the mains. It is very unlikely that this has gone bad.
Then plug in a mains bulb tester. power up the transformer through the mains bulb tester.
Tell us what you measure/find.
The X rated capacitor on the primary side is to suppress interference coming in from the mains. It is very unlikely that this has gone bad.
Hello.
I managed to remove the secondary connections from the PCB, powered it up, and within seconds the fuse blew. I tested this twice, and twice it blew.
Therefore the problem has to be the transformer doesn't it, as it is blowing the fuse with no load?
I have seen on the forum that someone used an 18VA output torroidal as a substitute transformer.
I now have the service manual, but I can't see the spec of the transformer in the Arcam Alpha, although it does seem to indicate an output of 33V.
Would something like this or this do the trick?
Thanks everyone for your help so far.
As you'll have guessed, I'm a bit of a novice at this, but will be over the moon to get this working.
I managed to remove the secondary connections from the PCB, powered it up, and within seconds the fuse blew. I tested this twice, and twice it blew.
Therefore the problem has to be the transformer doesn't it, as it is blowing the fuse with no load?
I have seen on the forum that someone used an 18VA output torroidal as a substitute transformer.
I now have the service manual, but I can't see the spec of the transformer in the Arcam Alpha, although it does seem to indicate an output of 33V.
Would something like this or this do the trick?
Thanks everyone for your help so far.
As you'll have guessed, I'm a bit of a novice at this, but will be over the moon to get this working.
Hi.
I really appreciate your help.
(I replaced the capacitor as suggested. This didn't help.)
I just thought I was doing the right thing. I disconnected the transformer from the downstream side and tested - or at least I thought I was.
I'm not sure what a mains bulb tester is, but I've been working on this problem with an electrician at work, and I guess he'll have one, so I'll see if I can get hold of one tomorrow morning to try out the transformer.
I'll let you know how I get on.
I really appreciate your help.
(I replaced the capacitor as suggested. This didn't help.)
I just thought I was doing the right thing. I disconnected the transformer from the downstream side and tested - or at least I thought I was.
I'm not sure what a mains bulb tester is, but I've been working on this problem with an electrician at work, and I guess he'll have one, so I'll see if I can get hold of one tomorrow morning to try out the transformer.
I'll let you know how I get on.
Sounds like you had a bit of an epic with the Arcam Alpha 3 in that thread! I have that manual now, which has a schematic of the Alpha, which documents +33v and -33v DC, but I can't establish what the AC output of the transformer should be to provide this.
As I say, I'm a novice at this, so I might be missing something.
Based on the serial numbers, I have an Alpha Plus.
In this thread, a 120va 2x18v transformer is used, but will 18v be high enough? I know 120va is right.
Many thanks.
As I say, I'm a novice at this, so I might be missing something.
Based on the serial numbers, I have an Alpha Plus.
In this thread, a 120va 2x18v transformer is used, but will 18v be high enough? I know 120va is right.
Many thanks.
You can remove the suppression capacitor and it will run fine. AndrewT - I have seen these go bad, usually when hit with a big enough spike.
One thing I have thought about - check for crap on the PCB around where the primary wires connect. I'm going on what the service manual shows but the clearances around there look rather tight.
I'm also wondering if it's possible someone has attempted to convert this to 120V and forgotten to mention it. Apparently, the service manual also says the fuse should be *800mA* antisurge! The service manual shows how the primaries should be wired for 240V operation. If you don't trust the PCB, you can always rewire it using some terminal block.
I have uploaded the service manual here. It's probably all you will get from Arcam anyway.
edit: DIYaudio, isnt censoring c-r-a-p a bit overkill?
One thing I have thought about - check for crap on the PCB around where the primary wires connect. I'm going on what the service manual shows but the clearances around there look rather tight.
I'm also wondering if it's possible someone has attempted to convert this to 120V and forgotten to mention it. Apparently, the service manual also says the fuse should be *800mA* antisurge! The service manual shows how the primaries should be wired for 240V operation. If you don't trust the PCB, you can always rewire it using some terminal block.
I have uploaded the service manual here. It's probably all you will get from Arcam anyway.
edit: DIYaudio, isnt censoring c-r-a-p a bit overkill?
A 2x18VAC transformer will give 25V power supplies when rectified. In practice this reduction in voltage will be OK, you will simply lose a little output power that you are unlikely to notice in practice. You could use 2x25VAC but that would require replacing C210/C211 with 50V/63V rated parts.
It depends how much you want to spend - I would say it is worth replacing the main capacitors as they will be pretty old by now and due for replacement. I am not sure how the original Alpha One has it's capacitors wired - a picture of the insides would be useful if you can manage it.
120VA sounds about right - the most important thing here is size. Measure the old one and pick a new transformer that will fit.
Suitable RS part codes are 223-8033 for the 2x18V transformer, and 223-8049 for the 2x25V transformer. They are 230V secondaries and not 115/230V secondaries so there will only be 2 primary wires to worry about.
It depends how much you want to spend - I would say it is worth replacing the main capacitors as they will be pretty old by now and due for replacement. I am not sure how the original Alpha One has it's capacitors wired - a picture of the insides would be useful if you can manage it.
120VA sounds about right - the most important thing here is size. Measure the old one and pick a new transformer that will fit.
Suitable RS part codes are 223-8033 for the 2x18V transformer, and 223-8049 for the 2x25V transformer. They are 230V secondaries and not 115/230V secondaries so there will only be 2 primary wires to worry about.
You have used a properly rated cap as a replacement haven't you. These are self healing and may not read faulty on a DVM.
Nothing else will do but you can safely remove it.
I find it hard to believe the trannys duff (it just doesn't happen really-on it's own anyway) but on the evidence so far I would suggest this.
If the trannys powered up (with secondaries disconnected) as Andrew says using the bulb and it lights then yes it's duff. Why ? If someone has fitted a 7.5 amp fuse the thing could have been cooking for ages. Does it smell ?
There is probably some underlying cause, maybe a bridge rectifier or smoothing cap, or perhap an output fault. It's strange that it did work OK at the start. And someones put the big fuse in for a reason. If it were an output fault then that would have packed up ages ago, and you would have heard it hum through the speakers, it wouldn't just have worked.
Nothing else will do but you can safely remove it.
I find it hard to believe the trannys duff (it just doesn't happen really-on it's own anyway) but on the evidence so far I would suggest this.
If the trannys powered up (with secondaries disconnected) as Andrew says using the bulb and it lights then yes it's duff. Why ? If someone has fitted a 7.5 amp fuse the thing could have been cooking for ages. Does it smell ?
There is probably some underlying cause, maybe a bridge rectifier or smoothing cap, or perhap an output fault. It's strange that it did work OK at the start. And someones put the big fuse in for a reason. If it were an output fault then that would have packed up ages ago, and you would have heard it hum through the speakers, it wouldn't just have worked.
Yep, i should have mentioned that - it must be an X2 rated capacitor for direct connection across the mains supply!
If push comes to shove, leave it out - it will just make some interference when you switch it on/off. A better place for the capacitor wouldve been across the switch contacts IMO.
If push comes to shove, leave it out - it will just make some interference when you switch it on/off. A better place for the capacitor wouldve been across the switch contacts IMO.
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