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Arcam Alpha 5 CD Player Distorted Analogue Output

Dowser said:
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?
Click to expand...
Yes, current output so no voltage swing on the opamp input, but uses I/V via OP27 opamp so pin 6 of each opamp should have voltage swing on them.
OP: Worth checking voltages on TDA chip. As a rough and ready measure you can see if there is any ac on these using your voltmeter: use DC setting to measure the DC volts, then on AC setting to check for gross ripple if you don't have a 'scope. Pins 27 & 28 are +5V, pin 26 is-5V and pin 15 is -15V
Hope this helps.
AP
 
And if you're poking around with a meter the opamps should have +15v/-15v on pins 7 and 4 (black probe to chassis/ground) and red probe to the pins).
 
Hi - thanks again for the thoughts. It would be great if you could listen to a sample. What is the easiest way to upload a file to share such a file ? I will load 2 samples - one with the analogue out and one with the digital out so you can also get an idea of the volume difference. I do have the service manual but I am a real beginner in terms of understanding it. I also have a meter but no scope. Agree that the fault must lie downstream from the DAC but that only helps to some extent as I understand the C416 capacitor only affects the analogue out - but why is this ? The power is right at the start of the journey ? Is C416/c406/c407 involved with the power supply for the DAC ?
 
C406 and C407 are part of the analogue section power supply, they are the smoothing capacitors that come after the rectifier. I've seen these fail on Arcam Alpha 5's many times.

C416 is part of the muting circuit IIRC. Again, this is a very common failure.

Since you have a meter check the voltages for us as detailed above.
 
Hi - so i got my meter out. All looks mainly well in that: for the 4 op amps (IC NE5534 x2 and IC OP27GN x2) I got -15v on pin 4 and +15v on pin 7 for all 4. So that sounds correct.
For the DAC Pin 28 +5v/ AC 10V peak cycling, Pin 27 +5v /AC 10V peak cycling, Pin 26 -5v /AC 10V peak, Pin 15 -15v /AC 16V (is this right ?) peak. Also all DC readings present and correct. The last AC value seems inconsistent with other AC readings ie no double the DC number.
 
Those DC voltages are all correct.

The op amps and DAC share the same power supply.
 
Hi Mike - what can I conclude from the voltages being correct ? Capacitors are all good ? Any thing else ?

Many thanks
 
I think that if you put it away 15 years ago and it was working ok that the fault is unlikely to be due to any of the semiconductors, far more likely the capacitors.

Time to lift out the pcb and check the caps?
 
Hi hp1 - I would be pleased / overjoyed if it were the caps. Visually they look brand new but may be that means nothing. How would I test if they are defective ? Also if the Voltages I tested are OK would this not suggest that the caps are OK ?
 
Alot of cheap multimeters have capacitance upto 200 uf ,you could do quick check with them in situ and just change them if they are way out.
 
Not mine unfortunately. I will need to buy one from Amazon. I will do so as the caps would be an easy fix.
 
If you go to the effort of removing the main PCB just replace the main smoothing caps and C416 while you're there. They'll need doing at some point anyway.

C403, 405, 406, 407 and C416.

Panasonic FC are widely available, not expensive and a decent choice.
 
That makes sense. I will get onto google and see who sell them. Do I need to upgrade the Voltage rating of the caps ?
 
Stick with the same form factor but you can use the same voltage rating or higher.
 
Blanco said:
Hi - so i got my meter out. All looks mainly well in that: for the 4 op amps (IC NE5534 x2 and IC OP27GN x2) I got -15v on pin 4 and +15v on pin 7 for all 4. So that sounds correct.
For the DAC Pin 28 +5v/ AC 10V peak cycling, Pin 27 +5v /AC 10V peak cycling, Pin 26 -5v /AC 10V peak, Pin 15 -15v /AC 16V (is this right ?) peak. Also all DC readings present and correct. The last AC value seems inconsistent with other AC readings ie no double the DC number.
Click to expand...

I’ve never used a DVM to measure AC on DC supplies, as I have a scope - but measured AC of 10v on a 5v DC rail sounds innacurate or suspect to me?
 
'AC 10V peak cycling' - this is a common problem with DVMs, they cannot cannot adequately separate the ac component from the DC - measuring via a small (10-47nF) cap can help by removing the DC component but this approach is difficult - the DVM's internal resistance is very large, 100megaohm or more, so you can wait for minutes for a sensible reading while the damn thing charges-up to null the dc!


So yes, as Dowser says, using an oscilloscopes is best. And PFM has actually has couple 'out there' in circulation for the asking :) - see the pinned posts near the top of the DIY forum. Whereabouts are you, @Blanco? there may be a helpful pfm soul within reach if you get really stuck :)
 
Hi Martin - I am in Hamburg so I think I may be out of range ! I have learnt so much from all of the comments and I now have a plan which is to Replace the 5 capacitors to see if these are the issue. If this does not work then I will need to see if I can convince myself that it is the DAC. (Not sure what else it could be given symptoms - digital output works) and then source a replacement DAC from a Philips player. Having said all of that, if it is not the caps then I can also look out for a cheap Alpha 5 or 6 on ebay here in Germany. I am not so mad keen on replacing the DAC chip given the cost and time involved.
 
Don't want to sidetrack the thread but I made some measurements on my CD160#2 using my Fluke 8026B (10Mohm input impedance) as follows:
Raw supplies:
+24.4Vdc (0.15Vac); -24.8Vdc (0.16Vac); +11.3Vdc (0.18Vac) and -12.4Vdc (0.13Vac). The ac voltages took about 5 seconds to settle. My scope shows these as 0.7 to 0.8V peak-to-peak so the above are not unreasonable.
Reg'ed supplies: +14.6Vdc; -15.4Vdc; +5.1Vdc and -6.0Vdc, all 0.1mVac.
Maybe I'm just lucky then, I don't know to be honest.
Blanco, as has been said above I would replace the main reservoir caps on the raw supplies as well as those on the regulator outputs. There is clearly not a lot wrong as the digital out works which indicates that the +5Vdc supply and SAA7220 are good. What DVM did you use?
Hope you can get it sorted.
Best,
AP
 
Hi AP - thanks for the comments. I am very grateful that the community here is happy to help me. I am travelling at the moment but my DVM is around 15 years old and cheap and made in China. I think it is a "Microtana". Certainly not a high quality instrument like a Fluke. All roads lead to replacing those caps. Best regards Blanco
 
With the lid removed and the front of the player facing you...

The biggest capacitor on the main PCB is between the DAC PCB and the transformer should be C403. If the player is standard I think this will be a pale blue Rubycon 3300uF 25v. It will be approx. 16 or 18mm mm in diameter and about 30-35mm tall. The lead pitch will be 7.5mm. This capacitor is the main filter cap for the positive rail of the digital power supply.

Right next to it, moving slightly toward the back of the player there should be a 1000uF capacitor. It will be about 12.5mm diameter, about 20mm tall and 5mm pitch. Again, a pale blue Rubycon. This is C405 and is the filter cap for the negative rail of the digital power supply.

Moving slightly further to the back there is a pair of 1000uF capacitors, same size as the C405. These are C406 and C407 and they are the filter caps for the analogue power supply to the DAC board. These two very often go bad.

Behind those is C416 which is 470uF. This is part of the muting circuit. It will be about 10mm diameter and about 16mm tall and 5mm pitch. This too very often goes bad.

All dimensions above are just estimates to help you find the parts. Please check the correct diameter before ordering new parts.

C403 - Replace with same diameter and pitch. A 25v part or higher. You can increase to 3900uF if you like for slightly better performance or stick with 3300uF.

C405 - Replace with same diameter and pitch. 25v or higher. You can increase to 1500uF for slightly better performance.

C406 and C407 - Replace with same diameter and pitch. From memory these are 25v rails so you should use 35v parts here. You can increase to 1500uF for slightly better performance. You can use the same part for C405 so buy x3.

C416 - Use same diameter and pitch. Use same voltage as original or higher (35v should be easy to buy and plenty). No benefit in increasing capacitance so stick to 470uF.

There are lots of suitable parts but only buy top quality e.g.

Panasonic FC, FR or FM series
Rubycon ZLH series
Nichicon PW or HE series​
 
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