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Arcam Alpha 5 - Distorted audio output

Discussion in 'd.i.y.' started by Jim3, Jul 16, 2007.

  1. Jim3

    Jim3 Member

    Hi,

    I've got a old Arcam Alpha 5 cd player that has developed a fault on its audio output.

    Just wondering if any body here has had a similar problem, or has any advice on how to go about repairing it.

    The player reads discs, skips tracks etc perfectly. I don't think that there is any problem with the drive, or pick up head. There is some audio output from the player, I can hear the music but it is almost completely saturated in heavy distortion. After an email to arcam spares department, they reccomend changing the TDA1541 DAC IC. Seems odd for an IC to go, they are usually very reliable, I would have thought it would have been something more along the lines of a dry solder joint or capcitor that has dried out.

    However, arcam obviously know a lot more about it than I do, so I will follow their advice and replace the TDA1541.

    I have searched the regular electronic component suppliers, rs, and farnell, but they don't stock the part. Any ideas where I can obtain a TDA1541?

    Any ideas or suggestions of where to start with the repair or sourcing the TDA1541 would be greatly appreciated.

    It would be a shame to see have to see the player consigned to the bin as it sounds really nice, and I would probably have to spend a fair few quid to get something that sounds as good.

    Thanks

    Jim
     
  2. mirland

    mirland pfm Member

    Mine had the same problem. Never got 'round to do anything about though so it's stacked up with all the other "needs some kind of repair" equipment :)
     
  3. Cesare

    Cesare pfm Member

    Jim,

    The first thing i'd do is to connect the digital out of the player to a DAC to check that the distortion is in the converter/analog domain.

    The Alpha 5 DAC is on a daughter card, so it should be easy to remove and work on.

    Cesare
     
  4. Jim3

    Jim3 Member

    Thanks for the reply.

    I have an old Kenwood mini disk player that has a digital coax in thats been in the loft since I ditched mini disc in favour of a pc with a cd burner.

    I will try connecting the alpha 5 to it when I get home from work and see what I get out of it.

    Hopefully I the fault will be in the audio stage as you say.

    I'm assuming the daughter board you mention is the smaller circuit board which is sort of floating (well not really floating, connected by some strange looking pins) above the main circuit board?
     
  5. chrisallan

    chrisallan Go on - bodge it!

    I'm sure Les said this was to do with 2 capacitors either near the output or near the psu. Look for leaky electrolytics as a starter.
     
  6. Fretless Eric

    Fretless Eric Musketeer Bathos

    Take the top off and look at the rear RHS from the front, you may find a burnt patch of the PCB by the culprit cap. This is a common problem and could be as you describe. The dig out is not affected.

    You can cure it by removing this part of the circuit quite easily, also removing the [unnecessary?] mute circuit at the same time.

    It would help if you had a copy of the service manual to find your way round. This is quite available on PFM and I probably have a copy myself if I look.

    Anyway, welcome Jim. Stick around and others will shower you with promises of another world starting with you Alpha 5.

    Found it, PM me with your email addy and I'll send the manual.
     
  7. Jim3

    Jim3 Member

    Thanks for all the replies.

    Thanks for the offer of the service manual Eric, I managed to get a copy of a service manual of arcam. Not really had time to study it properley yet though.

    I will have a look inside the machine when i get home and see if i can see any evidence of burnt compenents or circuit board.

    While I'm in the loft getting my Mini Disc player out to test the digital out, i think i better dust off my oscilloscope and signal generator, got a feeling it may be coming out of retirement for this job, that is if it still works!

    Thanks again everyone, I'll report back later when i've had a nosey inside the case.
     
  8. lostintheozone

    lostintheozone Cabin Boy

    I had a very similar problem due to poor connections between the mother board and the dac board a bit of cleaning and gentle wobbling got it sorted eventually - it wasn't a first time thing. However it didn't require that I replaced anything. So maybe worth a try first. Someone told me that the earth returns may not be good - not sure if that make any sense to those who know?

    Guy
     
  9. Jim3

    Jim3 Member

    Tested the digital output from the cd player using my old mini disc player; it works perfectly.

    Took the lid off and had a inspected what i could see of the circuit boards and compentents without removing the audio board.

    The audio board appears to have some sort of variable component, maybe a cap or a resistor at the rear right hand side of the audio board, just to the right of where the digital coax output exits through the back of the case. I assume its for some its for fine tuning and adjusting something.

    Anyway this component appears to have discoloured the part of the circuit board. It looks like its burnt. Does this this the culprit cap you mentioned Eric?

    I can take a picture of it and post it if you like?

    I left the schematics at work unfortunately, I shall have a look at them tmrw and try to figure out what the component is. Its labeled on the circuit board as "T201" so hopefully shouldn't be too hard to figure out what it is.

    Any idea how much a replacement is going to be?

    I'm reckoning about 2 quid tops if its just some generic variable cap or resistor. Hopefully if it is that part that has burnt out, its not taken anything else with it.

    Thanks again everybody for your suggestions.

    I shall let you know how i get on!
     
  10. RustyB

    RustyB Registered Ginga

    That sounds like the transformer for the digital o/p.

    If the player initially plays OK, then becomes rapidly noisy as it warms, it's bound to be the DAC chip. It is common for them to die. Try a search, I got one from eBay at a reasonable price. Make sure it's a TDA1541A.

    While you're at it, you should at least replace Z2 and Z102 with OP27's, and replace C13, C113 with a 4.7 uF film cap.
     
  11. Fretless Eric

    Fretless Eric Musketeer Bathos

    Jim3,
    The location you describe is on the daughter board not on the main board. I can't remember and have no photographs of this so can't help from the information you have given on this point. This could be a red herring.

    On the other hand, if it were the main board then it would suggest that it is the common problem and you could simply cut out the mute transistors Q2 and Q102 [left rear?] then you should get clean sound.

    From memory it think it was a cap in the power supply to the kill circuit [drg C02-0064, sht 1 of 3] possibly C416 so check the board here.

    You might want to lift the components if you really think you might want to reverse the mod but I can't remember how fiddly this is. Deletion of the transistors is considered to give a slight improvement in any case.

    Incidentally my copy of the service manual doesn't have a page 4 and that came from Arcam.

    As I suspected the mod suggestions have started. Well done RustyB :)
     
  12. mickhick1

    mickhick1 pfm Member

    I had an identical problem on an Alpha 5 which turned out to be the muting transistors. When they were disconnected, not only did the problem disappear but the sound improved dramatically.
    Arcam told me also that it could be the DAC and I had that replaced by Les W.

    Mike
     
  13. RustyB

    RustyB Registered Ginga

    Q2 and Q102 are the muting trans on the DAC board.
     
  14. Fretless Eric

    Fretless Eric Musketeer Bathos

    Quite right, but the cap that dies is on the main board.
     
  15. zanash

    zanash pfm Member

    Whats its part number ?
     
  16. Jim3

    Jim3 Member

    Had a look at the service manual this morning.

    RustyB was right, T201 is the digital o/p isolating transformer. Its mentioned in the Circuit description of the Audio Board in the service manual and is show on the circuit diagram.

    Thats some small ass transformer, the smallest I have ever seen! It looked like a pot to me.

    As the digital o/p is functioning correctly, this component can't be faulty. Transformers run warm so this would explain the discolouration of the circuit board around where T201 is seated.

    Looking at the block diagram in the service manual, and knowing that the digital output is working, the problem must be in either the TDA1541A (Z205), the I-V Conversion & Analogue Filters (Z1, Z101 OP27, Z2, Z102, NE5534) or the kill, coming in from the mute circuit.

    I think I will investigate the mute circuit this evening after work. Probably remove the transitors, desolder them, rather than cut them as I can put them back in again, if that doesn't cure it !

    Had a look on ebay for a DAC, there is a chap selling them for £15, bit pricey for an DAC if you ask me, but I suppose if it gets the job done then its worth it. I think, i'll investigate this mute circuit before I order a DAC though.

    In response to RustyB, the player doesn't start out playing okay and deteriorate rapidly, its always the same. Constant noise on the output regardless of the operating temperature.

    Eric, the sevice manual I received from Arcam is a 17 page pdf doc, I will email you a copy if you have found yours to be incomplete?

    Thanks again for the advice gents.

    I will try and get the soldering iron out and have a look at it tonight, unless the Mrs has other plans for me!

    I will report back once i've had a play with this mute circuit.

    Jim
     
  17. Fretless Eric

    Fretless Eric Musketeer Bathos

    But worth a check, as I say.

    Edit - I am at home now and I have a picture of a burnt PCB in front of me with black in the area around what looks like the C416 and R109. I think it is C416 that fails and if I remember correctly the chap at Arcam [very nice man] diagnosed it straight away off the top of his head over the 'phone so it must be such a common failure.

    Jim, check your manual as mine is 17 pages with page 4 missing...
     
  18. Jim3

    Jim3 Member

    Upon closer inspection of my copy of the service manual, page 4 is indeed missing.

    I found the cap C416 on the circuit diagram of the power supply, 470uF electrolytic. I shall try and find it on the actual circuit board when i get home.

    If it is this thats the problem, i take it that its just a like for like swap for a new one to cure it?
     
  19. Fretless Eric

    Fretless Eric Musketeer Bathos

    If it is then, yep.
     
  20. JonHarrison

    JonHarrison pfm Member

    Hi,

    Change C416 for a 35V (or greater) part. The 25V cap Arcam fitted is under rated in that position which is why it fails. It doesn't have to be anything special. Assuming it is the cause - if you look at the mute transistors you'll see that they are switching with the mains frequency which is the source of the distortion. When the cap fails the mains ripple feeds straight through to the mute circuit. If you're unlucky it will have leaked over the pcb.

    Lifting one leg of the base resistor would be easier than removing the mute transistor if you just want to check.

    Cheers,

    Jon
     

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