Hello All,
I am not an expert but trying to keep this amp from the skip.
The 1.25amp internal fuse keeps blowing (230v) and the only thing I am going to attempt to replace is the Toroidal Transformer. However, I cannot establish the type of transformer I need? Arcam themselves weren't interested but I did locate the manufacturer of the Transformer and they wanted a crazy £100 to send a replacement. They were also not inclined to divulge the specs.
I don't know if the toroidal transformer is the problem anyway and I can get a wide variety of differing spec transformers starting at £10.
I am not an expert but found an engineer service manual for the amp on the web and as far as I can tell, the output from the transformer to the circuit board is 2X9V? I don't know what "VA" is but it looks like anything from 15VA up to 100VA is available. The dimensions of the original transformer is about 100mm diameter and 35mm deep.
Is it worth pursuing this or is the problem likely to be elsewhere anyway? I was given the amp and don't know what the problem is other than it blows internal fuses.
Thanks!
I am not an expert but trying to keep this amp from the skip.
The 1.25amp internal fuse keeps blowing (230v) and the only thing I am going to attempt to replace is the Toroidal Transformer. However, I cannot establish the type of transformer I need? Arcam themselves weren't interested but I did locate the manufacturer of the Transformer and they wanted a crazy £100 to send a replacement. They were also not inclined to divulge the specs.
I don't know if the toroidal transformer is the problem anyway and I can get a wide variety of differing spec transformers starting at £10.
I am not an expert but found an engineer service manual for the amp on the web and as far as I can tell, the output from the transformer to the circuit board is 2X9V? I don't know what "VA" is but it looks like anything from 15VA up to 100VA is available. The dimensions of the original transformer is about 100mm diameter and 35mm deep.
Is it worth pursuing this or is the problem likely to be elsewhere anyway? I was given the amp and don't know what the problem is other than it blows internal fuses.
Thanks!
The transformer is not likely to be bad. Much more likely to be the problem are the large electrolytic capacitors.
Possibly, a bad rectifier diode.
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If the mains fuse blows, it is usually one of:
* bad power amplifier (probably with output transistors shorted)
* bad rectifier
* bad electrolytic capacitor that can't withstand full rail voltage any more or is dead short (would have to be one of the big 10000µ ones)
If you are lucky (and that's a big if), it's one of the latter two. Rectifiers are easy enough to test in-circuit with a multimeter's diode test function (in fact it's a bunch of discrete diodes here), and finding a dead short on one of the rails should not be much of a problem either - though you may have to test the output MOSFETs separately to find out whether they are at fault.
If it turns out to be a power amp problem, you're probably in over your head. The circuit doesn't look like it would be super hard to fix - no exotic parts or anything, literally just a bunch of bog standard BC547B/557B/546B/556B plus some IRF540s in the power stage - but it does take some experience which you are clearly lacking at this point.
* bad power amplifier (probably with output transistors shorted)
* bad rectifier
* bad electrolytic capacitor that can't withstand full rail voltage any more or is dead short (would have to be one of the big 10000µ ones)
If you are lucky (and that's a big if), it's one of the latter two. Rectifiers are easy enough to test in-circuit with a multimeter's diode test function (in fact it's a bunch of discrete diodes here), and finding a dead short on one of the rails should not be much of a problem either - though you may have to test the output MOSFETs separately to find out whether they are at fault.
If it turns out to be a power amp problem, you're probably in over your head. The circuit doesn't look like it would be super hard to fix - no exotic parts or anything, literally just a bunch of bog standard BC547B/557B/546B/556B plus some IRF540s in the power stage - but it does take some experience which you are clearly lacking at this point.
AGREE that you should be looking at rectifiers and caps, etc, before transformer. Disconnect transformer from its loads, tape the leads, and see if fuse holds. ( Lamp Limiter is a better idea.)
> I don't know what "VA" is
Essentially "power". VA are not Watts but for many purposes they are similar.
Note that Watts Audio Output is always less, sometimes much less, than Watts/VA pulled from the transformer.
> it looks like anything from 15VA up to 100VA is available.
You can get tiny 2VA jobs. 2,000VA is a stock item in toroidal. The amplifier does not actually care toroidal or E-I core. A 25,000VA transformer powers my house. They must have 500,000VA transformers at the dam generator.
VA generally goes by "size/weight". If you truly have a 20 pound dud, and you are looking at 2 pound toys, it aint going to work. Lawnmower engine in a heavy truck. Even if the RPM is right, the torque aint there.
> I don't know what "VA" is
Essentially "power". VA are not Watts but for many purposes they are similar.
Note that Watts Audio Output is always less, sometimes much less, than Watts/VA pulled from the transformer.
> it looks like anything from 15VA up to 100VA is available.
You can get tiny 2VA jobs. 2,000VA is a stock item in toroidal. The amplifier does not actually care toroidal or E-I core. A 25,000VA transformer powers my house. They must have 500,000VA transformers at the dam generator.
VA generally goes by "size/weight". If you truly have a 20 pound dud, and you are looking at 2 pound toys, it aint going to work. Lawnmower engine in a heavy truck. Even if the RPM is right, the torque aint there.
The schematic shows that the 9V winding is only for small 5V dc supply to the the microcontroller and remote volume control motor. The main amplifier power is a centre tapped winding identified by 3 wires (orange, orange, blue) as shown. Any direct replacement would need to have both the single 9V and the centre-tapped 50VAC winding (or dual windings of approx. 25VAC each. The VA rating for 2 x 40W/8 ohms amplifiers would need to be at least 120VA (a standard 160VA would be ideal but skimping on transformers is legend with many manufacturers.
If you want to find out whether there is a problem with the transformer, the obvious way is to disconnect it from the rectifier and the rest of the amp. Note there are connectors to make that simple, SK7 & 8. 'not sure what "cage clamp" means in that application but I assume it means connector rather than soldered or crimped joint. In any case, label the leads so there is no chance of forgetting which connects to what, then disconnect them and recheck the status. I'd be surprised if the transformer blew any fuses now.
If you are tired of blowing fuses (note only 1 is used), be sensible and fit a lightbulb limiter as advised time and time again on this forum - Google it 🙂
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Don't change anything yet.
Build up a Mains Bulb Tester.
Use it to power ON the Arcam.
If there is a serious overcurrent event the Bulb will light up and limit the input voltage drastically. This prevents the fuse blowing and prevents further damage to internal components.
You can then measure the output voltages of the transformer's secondary windings.
Report back when you have done this.
Build up a Mains Bulb Tester.
Use it to power ON the Arcam.
If there is a serious overcurrent event the Bulb will light up and limit the input voltage drastically. This prevents the fuse blowing and prevents further damage to internal components.
You can then measure the output voltages of the transformer's secondary windings.
Report back when you have done this.
Hi rabbitz. No clear indication of the fuse type on schematic or parts list. It seems 1S2A5 is on the schematic is a code unique to Arcam but the parts list calls for "FUSE 20mm 1.25A AS" There is no suggestion on the net that this means anything more than a standard (fast blow) type.
For interest, here's why you don't want to replace the transformer on this series of Arcam amplifiers, if you can possibly avoid it - yep, a truly inspired piece of high-tech assembly 🙄
For interest, here's why you don't want to replace the transformer on this series of Arcam amplifiers, if you can possibly avoid it - yep, a truly inspired piece of high-tech assembly 🙄
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Thanks everyone for the prompt replies and sage advice. Yes, I am definitely in way over my head and think it best this amp is broken up into PCBs metals plastics and recycled.
To answer the questions posed:
Yes, the Transformer was a challenge to remove and I carefully sliced through the sticky securing material with a blade.
The Internal fuse would blow immediately upon power up, at zero volume with nothing connected.
I shall look to going down the lightbulb path in lieu of a fuse if I am given another dud to play with in the future 😱)
I had a look at the capacitors previously, I have successfully replaced "bloomed" and bulging small electronics caps in the past, bring LCD TVs, Graphics cards, motherboards and Computer PSUs back to life - these two large items "look" fine but who knows.
Thanks again for the responses.
Joe
To answer the questions posed:
Yes, the Transformer was a challenge to remove and I carefully sliced through the sticky securing material with a blade.
The Internal fuse would blow immediately upon power up, at zero volume with nothing connected.
I shall look to going down the lightbulb path in lieu of a fuse if I am given another dud to play with in the future 😱)
I had a look at the capacitors previously, I have successfully replaced "bloomed" and bulging small electronics caps in the past, bring LCD TVs, Graphics cards, motherboards and Computer PSUs back to life - these two large items "look" fine but who knows.
Thanks again for the responses.
Joe
Now that you have the transformer disconnected from the load, try the Mains Bulb Tester to see what the transformer does.
Does the bulb light up, or does it glow dimmly, or flash briefly to become dim, or no glow at all?
Those 4 different results indicate different conditions. Test it.
Does the bulb light up, or does it glow dimmly, or flash briefly to become dim, or no glow at all?
Those 4 different results indicate different conditions. Test it.
Epilog
Arcam very kindly got back in touch with me over the transformer and the PDF schematic dating from 1997 shows the Voltages to be 27.2v coming out. So, no standard Toroidal I found would have worked anyway.
The Arcam Alpha 7 is therefore regrettably going to be recycled.
I can upload the PDF if anyone is interested - about 57kb.
Arcam very kindly got back in touch with me over the transformer and the PDF schematic dating from 1997 shows the Voltages to be 27.2v coming out. So, no standard Toroidal I found would have worked anyway.
The Arcam Alpha 7 is therefore regrettably going to be recycled.
I can upload the PDF if anyone is interested - about 57kb.
Seems a shame to bin it.
As others have mentioned, the transformer is not the most likely suspect in all this and is dead easy to prove one way or the other. Just power up with secondary's disconnected. If the tranny is duff it will still blow the mains fuse.
As others have mentioned, the transformer is not the most likely suspect in all this and is dead easy to prove one way or the other. Just power up with secondary's disconnected. If the tranny is duff it will still blow the mains fuse.
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