I have an Arcam Delat 290 that has been working fine for many years. Recently I was careless when moving speakers and the red and black speaker cables touched while the AMP was switched on causing it to cut out.
Now I can't get the amp to power up - it just blows the fuse each time (the T1A6 surge protect fuse inside the amp).
Can anyone suggest what might be the cause of this and offer some suggestions for diagnosing or fixing the problem.
I am not an electronics expert - but would be happy to attempt diy repairs if necessary. I have a volt/amp/resistance meter..
Thanks in advance for any advice...
Sean Kenwrick
Now I can't get the amp to power up - it just blows the fuse each time (the T1A6 surge protect fuse inside the amp).
Can anyone suggest what might be the cause of this and offer some suggestions for diagnosing or fixing the problem.
I am not an electronics expert - but would be happy to attempt diy repairs if necessary. I have a volt/amp/resistance meter..
Thanks in advance for any advice...
Sean Kenwrick
Sean,
Replace the blown fuse with another 1.6Amp anti-surge. Turn the volume down to minimum and switch both speaker outputs off. Then, with all inputs and outputs disconnected from the amp (i.e. input phonos and speaker output cables removed) power on.
If I remember correctly the power led starts off orange and then after a short while the output relays click and the led changes to green. At what point does the fuse blow ?
Jon
Replace the blown fuse with another 1.6Amp anti-surge. Turn the volume down to minimum and switch both speaker outputs off. Then, with all inputs and outputs disconnected from the amp (i.e. input phonos and speaker output cables removed) power on.
If I remember correctly the power led starts off orange and then after a short while the output relays click and the led changes to green. At what point does the fuse blow ?
Jon
Sean,
I believe the amp has an IC that protects the output against overload, it is possible though that the output transistors or something else in the output stage has failed short circuit following your accident.
The amp runs on +/-44V rails. With the amp off measure the resistance between +44 and 0V and -44V and 0V. There are three wires running from the toroid to the pcb, you can measure these. If you measure 0 ohms between either pair then you have found the short and the reason the fuse keeps blowing. Are you able to remove the output transistors from the pcb (there should be four bolted to a large heatsink), then try measuring the resistance again ? I'm afraid I don't know which of the transistors are left channel / right channel or positive / negative but perhaps you can work this out for yourself. It may be that one or all have failed.
Do you know which version of the amp you have? What is the serial number? Arcam used different transistors during the lifecycle.
Jon
I believe the amp has an IC that protects the output against overload, it is possible though that the output transistors or something else in the output stage has failed short circuit following your accident.
The amp runs on +/-44V rails. With the amp off measure the resistance between +44 and 0V and -44V and 0V. There are three wires running from the toroid to the pcb, you can measure these. If you measure 0 ohms between either pair then you have found the short and the reason the fuse keeps blowing. Are you able to remove the output transistors from the pcb (there should be four bolted to a large heatsink), then try measuring the resistance again ? I'm afraid I don't know which of the transistors are left channel / right channel or positive / negative but perhaps you can work this out for yourself. It may be that one or all have failed.
Do you know which version of the amp you have? What is the serial number? Arcam used different transistors during the lifecycle.
Jon
There are three cables coming from the toroid (blue,green,blue) and I measured the resistance between the blue and green cables (for both blue cables).
I set it to the lowest setting (200 Ohms) and it is showing 01.6 for both cables. I guess this means a resistance of 1.6 ohms between the blue and green cables.
Do you think that this indicates a short? It is not zero but I get 00.8 from just touching the probes together.
I have unbolted the mosfet transistors from the heat sink but they don't seem to want to come out. Are they soldered into the PCB? If so I guess I will have to get the PCB out which looks like quite a tricky job since all the output connectors and switches woould have to be removed as far as I can tell.
If you think that they should just pop out then I might try applying a bit more force...
Let me know what you think..
thanks
Sean
I set it to the lowest setting (200 Ohms) and it is showing 01.6 for both cables. I guess this means a resistance of 1.6 ohms between the blue and green cables.
Do you think that this indicates a short? It is not zero but I get 00.8 from just touching the probes together.
I have unbolted the mosfet transistors from the heat sink but they don't seem to want to come out. Are they soldered into the PCB? If so I guess I will have to get the PCB out which looks like quite a tricky job since all the output connectors and switches woould have to be removed as far as I can tell.
If you think that they should just pop out then I might try applying a bit more force...
Let me know what you think..
thanks
Sean
Sean,
>0.8ohms. Do you think that this indicates a short?
Pretty close but I probably should have actually asked you to measure it on the pcb having disconnected the blue/green wires first sorry. What you have measured is everything across the supply in parallel with the secondary of the transformer which itself will have a low resistance. If you can disconnect the wires and measure again please do. Depending upon which way round you have the probes you'll probably see the resistance changing as you charge up the caps.
>I have unbolted the mosfet transistors from the heat sink but they don't seem to want to come out. Are they soldered into the PCB?
Yes! Don't tug on them, they will need to be desoldered.
>I will have to get the PCB out which looks like quite a tricky job since all the output connectors and switches woould have to be removed as far as I can tell.
You shouldn't have to take any knobs off. I think you can unscrew the front facia from behind or the side and pull this forward. The phonos are screwed to the rear panel by a few screws and the pcb is screwed to the chassis by a few more screws. Once you have removed all of the screws the pcb should just pull forward and up away from the chassis. The toroid is heavy!
Jon
>0.8ohms. Do you think that this indicates a short?
Pretty close but I probably should have actually asked you to measure it on the pcb having disconnected the blue/green wires first sorry. What you have measured is everything across the supply in parallel with the secondary of the transformer which itself will have a low resistance. If you can disconnect the wires and measure again please do. Depending upon which way round you have the probes you'll probably see the resistance changing as you charge up the caps.
>I have unbolted the mosfet transistors from the heat sink but they don't seem to want to come out. Are they soldered into the PCB?
Yes! Don't tug on them, they will need to be desoldered.
>I will have to get the PCB out which looks like quite a tricky job since all the output connectors and switches woould have to be removed as far as I can tell.
You shouldn't have to take any knobs off. I think you can unscrew the front facia from behind or the side and pull this forward. The phonos are screwed to the rear panel by a few screws and the pcb is screwed to the chassis by a few more screws. Once you have removed all of the screws the pcb should just pull forward and up away from the chassis. The toroid is heavy!
Jon
Sean,
Rather than measuring at the input you could approach the problem from the other end. If you can get to them you could actually measure the output mosfets. Measure the resistance between the three legs of each device (left-right,left-middle,right-middle). I they are working correctly then I don't think any measurement should be less than a few hundred ohms, say about 500-600 or so.
Jon
Rather than measuring at the input you could approach the problem from the other end. If you can get to them you could actually measure the output mosfets. Measure the resistance between the three legs of each device (left-right,left-middle,right-middle). I they are working correctly then I don't think any measurement should be less than a few hundred ohms, say about 500-600 or so.
Jon
Hi
There are 4 mosfets - the two nearest the back measure 300-600 ohms when I test all combinations. The two nearest the front measure nearly zero between the middle and right legs and only a few ohms between the others. This is with the AMP switched off.
I have now removed the PCB as you described but the soldering iron that I am sure have seen every day for the last 10 years has disappeared into the ether so I will have to purchase a new one.
I guess it is these two transistors that need replacing right? On the front is printed: IRFP240 - I will try and source these tomorrow....
Cheers
Sean
There are 4 mosfets - the two nearest the back measure 300-600 ohms when I test all combinations. The two nearest the front measure nearly zero between the middle and right legs and only a few ohms between the others. This is with the AMP switched off.
I have now removed the PCB as you described but the soldering iron that I am sure have seen every day for the last 10 years has disappeared into the ether so I will have to purchase a new one.
I guess it is these two transistors that need replacing right? On the front is printed: IRFP240 - I will try and source these tomorrow....
Cheers
Sean
Hi Sean,
>I guess it is these two transistors that need replacing right?
For starters yes but it is of course possible that more of the output stage on that channel has been taken out as well, like the pre-driver transistors for example.
I don't know how well the output mosfets need to be matched to get good performance from the amp. I also don't know what Arcam did on the assembly line, they may have sorted them into matched pairs or simply fitted the next pair out of the tube. I'd expect four from the same batch to be a closer match to each other than four from two seperate production batches though so if you can stretch to the extra £10 I'd replace all four. I'm probably worrying about nothing here but you'll be able to hear if there's a problem with increased distortion when the amp is working again anyway.
You should be able to power the amp up with the blown mosfets removed without doing any more damage to the amp - to see if the fuse blows again. At least this should give an indication of whether anything else has gone. The two at the back sound ok so you could just desolder the two at the front if you want to try this - unless you've decided to replace them all that is.
Jon
>I guess it is these two transistors that need replacing right?
For starters yes but it is of course possible that more of the output stage on that channel has been taken out as well, like the pre-driver transistors for example.
I don't know how well the output mosfets need to be matched to get good performance from the amp. I also don't know what Arcam did on the assembly line, they may have sorted them into matched pairs or simply fitted the next pair out of the tube. I'd expect four from the same batch to be a closer match to each other than four from two seperate production batches though so if you can stretch to the extra £10 I'd replace all four. I'm probably worrying about nothing here but you'll be able to hear if there's a problem with increased distortion when the amp is working again anyway.
You should be able to power the amp up with the blown mosfets removed without doing any more damage to the amp - to see if the fuse blows again. At least this should give an indication of whether anything else has gone. The two at the back sound ok so you could just desolder the two at the front if you want to try this - unless you've decided to replace them all that is.
Jon
The problem is solved!!
I replaced the mosfets and my AMP is back working again. It sounds fine to me so there doesn't seem to be any problem not having exactly the same mosfets as the other two. Perhaps these drive the second set of speaker outputs?
Anyway - many thanks for your help with this matter...
Best Regards
Sean
I replaced the mosfets and my AMP is back working again. It sounds fine to me so there doesn't seem to be any problem not having exactly the same mosfets as the other two. Perhaps these drive the second set of speaker outputs?
Anyway - many thanks for your help with this matter...
Best Regards
Sean
Hi Sean,
Glad to hear you've fixed it!
The two mosfets you've replaced provide the output for one channel. The two sets of speaker outputs are simply wired in parallel. The amp has a quasi-complimentary class AB output stage so that's why there are four N channel mosfets on the heatsink.
The earlier Delta290s had a pot to adjust the quiescent current but the later version (like yours I think) has an automatic bias circuit so no adjustments are required to set the idle current. Still though, having changed only one pair of mosfets the left and right channels may be less well matched now than they were before.
Regards,
Jon
Glad to hear you've fixed it!
The two mosfets you've replaced provide the output for one channel. The two sets of speaker outputs are simply wired in parallel. The amp has a quasi-complimentary class AB output stage so that's why there are four N channel mosfets on the heatsink.
The earlier Delta290s had a pot to adjust the quiescent current but the later version (like yours I think) has an automatic bias circuit so no adjustments are required to set the idle current. Still though, having changed only one pair of mosfets the left and right channels may be less well matched now than they were before.
Regards,
Jon
Another one.....
I recently purchased an Arcam Delta 290 on eBay. Got it for next to nothing because it was advertised as not powering up. Today I opened it up and went straight to the fuse. It was blown - BUT - when I removed it, it was a 5A (T5) instead of the recommended 1.6A (T1A6). Someone has tried to test or solve the problem by upping the fuse.
As I don't know what caused this problem - where should I begin?
Is following the advice in this thread a good way to start - in light of me not knowing if the speaker wires were shorted or not?
Any suggestions would be most appreciated.
Thanks.
Fin
I recently purchased an Arcam Delta 290 on eBay. Got it for next to nothing because it was advertised as not powering up. Today I opened it up and went straight to the fuse. It was blown - BUT - when I removed it, it was a 5A (T5) instead of the recommended 1.6A (T1A6). Someone has tried to test or solve the problem by upping the fuse.
As I don't know what caused this problem - where should I begin?
Is following the advice in this thread a good way to start - in light of me not knowing if the speaker wires were shorted or not?
Any suggestions would be most appreciated.
Thanks.
Fin
Hi,
As you can see from the above thread I had a similar problem. In my case it was due to the speaker cables touching and blowing the output circuits (perhaps the Delta290 is susceptable to this?)
Anyway the solution in my case was as follows:
Locate the 4 MOFSET transisters that are clamped to the heat sink box in the centre of the unit. They are flat, square, dark grey components with 3 pins clamped with a small metel strip to the heat sink.
Aquire an Ohm meter and measure the resistance between the middle and outer legs. In my case the two MOFSETs nearer to the front of the amp were fine (450-600ohms between middle and outer legs). But the two near the back had nearly zero resistance (a couple of ohms at most).
I therefore unscrewed the front panel and rear screws and removed the PCB (not as hard as it first looks - just make a note of which size screws go where (otherwise it takes a bit longer to put back together as I found to my cost!)).
Then unsolder the faulty MOFSETs and replaced with new ones of the same type. Unfortunately I can't find any record of my order for these - I must have ordered them over the phone, but I had no trouble locating the same ones for about £4.00 each.
It was recommended to me that I replace all 4 but I had already only ordered 2 and I can't hear any difference in the sound. You might want to replace them all though....
You can get the fuses from www.cricklewoodelectronics.com
If this doesn't help then post a message on the main forum and you will get alot of help from the guys here....
Good luck - this is a great amp so its worth tyhe effort.....
As you can see from the above thread I had a similar problem. In my case it was due to the speaker cables touching and blowing the output circuits (perhaps the Delta290 is susceptable to this?)
Anyway the solution in my case was as follows:
Locate the 4 MOFSET transisters that are clamped to the heat sink box in the centre of the unit. They are flat, square, dark grey components with 3 pins clamped with a small metel strip to the heat sink.
Aquire an Ohm meter and measure the resistance between the middle and outer legs. In my case the two MOFSETs nearer to the front of the amp were fine (450-600ohms between middle and outer legs). But the two near the back had nearly zero resistance (a couple of ohms at most).
I therefore unscrewed the front panel and rear screws and removed the PCB (not as hard as it first looks - just make a note of which size screws go where (otherwise it takes a bit longer to put back together as I found to my cost!)).
Then unsolder the faulty MOFSETs and replaced with new ones of the same type. Unfortunately I can't find any record of my order for these - I must have ordered them over the phone, but I had no trouble locating the same ones for about £4.00 each.
It was recommended to me that I replace all 4 but I had already only ordered 2 and I can't hear any difference in the sound. You might want to replace them all though....
You can get the fuses from www.cricklewoodelectronics.com
If this doesn't help then post a message on the main forum and you will get alot of help from the guys here....
Good luck - this is a great amp so its worth tyhe effort.....
Hi Sean
Thanks for the fast reply and all of the detailed info.
I'll try doing some measurements with the multimeter tomorrow. Still got one of these
in my head from New Year celebrations last night.
Hopefully this fault will be as easy to solve as yours was - and the use of a 5amp fuse hasn't done more damage. If it is the same fault and I replace all four mosfets, I wonder if there is some upgrade that is worthwhile - maybe a better quality or higher rated replacement part.
Fin
Thanks for the fast reply and all of the detailed info.
I'll try doing some measurements with the multimeter tomorrow. Still got one of these
in my head from New Year celebrations last night.Hopefully this fault will be as easy to solve as yours was - and the use of a 5amp fuse hasn't done more damage. If it is the same fault and I replace all four mosfets, I wonder if there is some upgrade that is worthwhile - maybe a better quality or higher rated replacement part.
Fin
Update
OK - I did the recommended measurements on the mosfets. The pair at the rear were identical and measured about 580 ohms between middle and right legs - and about 800 ohms between middle and left legs. The two mosfets near the front of the amp measured much less. The highest reading I got was 14 ohms.
After removing the clamp to the heatsink, I cut the legs of both front mosfets, then inserted a new 1.6A fuse. VOILA - it powered up, the orange led came on - then it turned green. I could hear the relays switching and all seems well.
I assume that this amp was subjected to the same mishap as Sean's. Now I just need to get some new mosfets. The ones I removed were manufactured by STMicroelectronics and don't seem to be available any more. I can get some made by IR - so I assume it would be better to replace all four.
(BTW - I'm in Australia - so some parts are harder to get here. It's often easier to order from the US)
I think that my amp is one of the older ones - so I wonder if it needs some adjustment of the idle current as mentioned by Jon Harrison.
Thanks again for this great info and help.
Fin
OK - I did the recommended measurements on the mosfets. The pair at the rear were identical and measured about 580 ohms between middle and right legs - and about 800 ohms between middle and left legs. The two mosfets near the front of the amp measured much less. The highest reading I got was 14 ohms.
After removing the clamp to the heatsink, I cut the legs of both front mosfets, then inserted a new 1.6A fuse. VOILA - it powered up, the orange led came on - then it turned green. I could hear the relays switching and all seems well.
I assume that this amp was subjected to the same mishap as Sean's. Now I just need to get some new mosfets. The ones I removed were manufactured by STMicroelectronics and don't seem to be available any more. I can get some made by IR - so I assume it would be better to replace all four.
(BTW - I'm in Australia - so some parts are harder to get here. It's often easier to order from the US)
I think that my amp is one of the older ones - so I wonder if it needs some adjustment of the idle current as mentioned by Jon Harrison.
Thanks again for this great info and help.
Fin
Hi Sean and Jon
I didn't get around to replacing the damaged MOSFETS yet - but I decided to test the Arcam amp to see if one of the channels was working and producing sound - before I go pulling it apart and reassembling, just to find that something else is broken.
Anyway, connected up a cdp and speakers - then switched on. The left channel works perfectly - so the damaged MOSFETS must be for the right channel. However, I also heard some distortion and crackles. Using the balance control, I determined that it was only coming from the right channel - along with some music. I was only expecting sound from one channel. Does this seem right for a channel without MOSFETS?
I will eventually pull out the pcb and replace the MOSFETS. I was just too curious to find out if the rest of the amp works........and it also gives us the following answer is:-
Front Mosfets are right, rear Mosfets are left.
I didn't get around to replacing the damaged MOSFETS yet - but I decided to test the Arcam amp to see if one of the channels was working and producing sound - before I go pulling it apart and reassembling, just to find that something else is broken.
Anyway, connected up a cdp and speakers - then switched on. The left channel works perfectly - so the damaged MOSFETS must be for the right channel. However, I also heard some distortion and crackles. Using the balance control, I determined that it was only coming from the right channel - along with some music. I was only expecting sound from one channel. Does this seem right for a channel without MOSFETS?
I will eventually pull out the pcb and replace the MOSFETS. I was just too curious to find out if the rest of the amp works........and it also gives us the following answer is:-
Front Mosfets are right, rear Mosfets are left.
I read somewhere on this forum that this is due to the signal leaking into ground....
I have received another pair of IRFP240s myself and I am going to change the MOSFETs on the left channel since I believe that Jon was correct in asserting that I should have changed all 4 of mine when I lost the right channel on mine Arcam Delta 290.. In fact the new right channel sounds better than the old left channel which has a different brand of MOSFET
Sean
I have received another pair of IRFP240s myself and I am going to change the MOSFETs on the left channel since I believe that Jon was correct in asserting that I should have changed all 4 of mine when I lost the right channel on mine Arcam Delta 290.. In fact the new right channel sounds better than the old left channel which has a different brand of MOSFET
Sean
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