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Arcam Alpha 5 CD Player Distorted Analogue Output

Discussion in 'd.i.y.' started by Blanco, Aug 29, 2019.

  1. Blanco

    Blanco Member

    Hi

    I got out my Arcam Alpha 5 cd players after 15 years of inactivity to find that it still worked apart from a broken cog wheel to open the drawer. I was rather pleased with myself when I found a thread on how to replace it and did so.

    However, having done so, soon after the analogue output failed suddenly having previously worked perfectly. Both channels are relatively quiet and highly distorted. The digital output works perfectly. I guess this is the risk when you use old hifi after a 15 year pause.

    I wondered if anyone would have an idea as to what it might be ? I have seen reference to Capacitor C416 near the PSU failing but the capacitor looks clean and does not appear to have leaked. However could it still have failed ?

    I have also read about upgrading components which would be worth it while I am trying to repair it.

    Grateful for any ideas.
     
  2. Mike P

    Mike P pfm Member

    Could be a failing TDA1541A DAC chip.

    Does the distortion get slightly worse/better as the player warms up from cold?
     
  3. hp1

    hp1 pfm Member

    As Mike says, its usually the first thing to fail on an alpha 5,sorry the second after the drawer gear.
     
  4. Mike P

    Mike P pfm Member

    It can be repaired of course.

    The problem is that the Alpha 5 doesn't have a proper power switch. Even when 'turned off' some sections stay powered up massively shortening the life of some components. I recommend always turning off at the plug socket.
     
  5. MJS

    MJS Trade: Consultant at WH Audio

    I've got a Naim CDI with a TDA1541A chip. That's been powered almost continuously for 28 years and it's still on the original chip. Since doing Martin's mods to the power supplies around it I've added a small heatsink on top of it to keep it a little cooler. I believe it's the thermal cycling of these chips that contribute to their failing. Any distorted output with these chipsets is always the DAC failing. By playing a sinewave from a CD you can clearly see the missing bits as it warms up.

    Beware that a lot of these DACs still available are the R1 version which is relaxed specification, up to 2 LSB error IIRC. A donor Philips or Marantz player will yield decent replacements although their life cannot be guaranteed.
     
  6. Mike P

    Mike P pfm Member

    On the Naim players the generous copper groundplain helps them run cooler.
     
  7. Blanco

    Blanco Member

    Hi Mike and MJS - thanks for your thoughts. I have not run it for very long to know whether it gets better or worse. I was too worried whatever it was could damage my amp or speakers. I will run it with the cables out and then plug them in and let you know if there is a difference. I have not used the CD for 15 years so I think it was well used for 5 or 6 years and then unused for 15. I did not unplug it from the mains when I did dig it out again so yes the DAC got power for 3 weeks.
     
  8. Blanco

    Blanco Member

    I should also say that sourcing the TDA1541A DAC chip is not easy - there are a lot of fakes. Do you have any ideas ? Also can I do any sort of test to prove it is the DAC - I did take the whole thing apart to mend the cog so may be I damaged something else or put back together incorrectly - eg the pins connection the DAC board to the the main motherboard. The digital out works perfectly. Thanks for all your thoughts.
     
  9. Mike P

    Mike P pfm Member

    The symptoms of failure of the TDA1541A DAC chip is static like distortion which is usually temperature related and gets worse as the chip warms up. A squirt of freezer spray on the DAC chip can often make the distortion lessen for a few moments until it warms up again.

    It should be safe to leave it plugged into to your system, the output coupling caps will block any DC on the output.

    Yes it could be something as simple as a dry joint. In particular check around the PCB mounted RCA sockets of the analogue output.
     
  10. Blanco

    Blanco Member

    Hi Mike - this is a very muffled distorted sound. The output is low so I need to crank up the volume to hear a muffled distorted output. I will have a look at the RCA outputs as these would have had some pressure on them when I reattached the DAC board onto the main board - the RCAs are wedged against the back of the case until the board is fully pushed down. Thanks again for all your tips which are extremely helpful.
     
  11. Mike P

    Mike P pfm Member

    My best guess would still be a knackered TDA1541 chip.

    The other common issue is dead caps on the mainboard brought about because of the lack of proper on/off switch. Check C406 and C407 as well as C416 which you already know about.

    Before you attempt to replace the DAC chip please make sure you're entirely confident in your soldering skills. It's very easy to lift the delicate pads/traces around the DAC chip if you don't know what you're doing.
     
  12. Blanco

    Blanco Member

    Ok - so I will have a look at the caps and the RCAs - if they look good then I will try to run the DAC for a bit to see if it gets worse. I am certainly no expert with a soldering iron - an amateur who occasionally solders. I will think long and hard before attempting this repair. I saw the suggestion to put a chip holder on to the PCB which is a good idea but does not help with the point that you make. Given the digital output works and I have a decent DAC and it sounds superb - may be the risk of breaking it completely or fitting a faulty / fake chip will put me off.
     
  13. Mike P

    Mike P pfm Member

    I can replace the TDA1541 with a genuine chip for you if you decide you want it done. Send me a PM.
     
    hifi-dog likes this.
  14. Dowser

    Dowser Learning to bodge again..

    I can sell you a genuine chip, maybe Mike can too. Key is to make sure it is the dac first - if you do not have freezer spray (a quick squirt resolved the 2 failed chips I’ve had through my hands), then switch it off for 24 hours (mains lead removed). If it works fine for 1st 1-5 mins then distortion starts, almost certainly DAC. You can also stick a heat sink on top of the chip which will sometimes keep the distortion away for a bit longer (beware buying 1541 players with heat sinks attached unless they are Cambridge audio...or you know/trust the person who modded it :))
     
    Mike P likes this.
  15. martin clark

    martin clark pinko bodger

    Notwithstanding the diverse great advice already given - first - just check any chip of any kind fitted in a socket - is already fully seated.
     
  16. yairf

    yairf pfm Member

    I would start by testing (and replacing if necessary) the lytic caps that are situated near the regulators. These caps get toasted by the heat emanating from the tiny heat sinks of those regs.
    If you’ve covered that part, and the distortion is still there, start looking for a replacement dac.
    Yair
     
  17. Blanco

    Blanco Member

    Hi - many thanks for all of the tips. I had the power cord out 48 hours and then powered it up and played a cd through the analogue out. Exactly the same result - muffled and quiet sound but distorted - no different from the sound when the power cord was in continuously. However, perfect through the digital out. All of the capacitors look brand new when viewed from above / the side. There is no obvious damage or leakage onto the pcb from above. I am not sure how to test the capacitors without actually taking them out ? I could also take out the entire PCB to look underneath but would prefer not to if I can avoid it.
     
  18. Dowser

    Dowser Learning to bodge again..

    Hmmm - then maybe not the DAC itself. Muffled doesn't sound right, but to be sure you could provide a link to a WAV file and we could check? If you have a meter, start checking voltages around analogue output stage. If you have a scope you can also use that to trace signals out of DAC into first opamps (can't remember if you'll get a signal on audio out of DAC, it's current output so a very low signal. I assume you have a service manual?
     
  19. martin clark

    martin clark pinko bodger

    The digital out put comes from the digital filter (SAA7220) not the dac chip so is unaffected by anything at the dac or after it. So that's where the issue lies.
     
  20. hp1

    hp1 pfm Member

    The dac chip failing usually sounds a bit like rain and gets worse over a period of a few minutes after switch on and not always on both channels.
     
    Mike P likes this.

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