Arcam Alpha 5 need help for repair - diyAudio
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Old 29th March 2013, 08:54 PM   #1
AMTL is offline AMTL  Canada
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Join Date: Mar 2013
Default Arcam Alpha 5 need help for repair

Hi,

I'm new to this forum. I have read a lot in the last few days and want to attempt repairing some broken electronics I have sitting around. I don't have much experience but I want to learn. I can solder ok but I may need help in reading schematics and understanding circuits better.

So the first subject is an Arcam Alpha 5 cdp. There is a problem in the DAC or ouput section because when I use the digital output with an external DAC it plays fine.

what happens is when it's cold it plays well but as it warms up, it still plays the music but adds some artifacts over it, only a little at first but it gets worse and after a few minutes it's getting close to continuous white noise.

I opened the player but did not notice anything special (no leaking cap, nothing loose). The design is such that there is a daughter board where the D/A conversion is done, using a tda1541a, and I guess the culprit is on that board.

Does anyone have an idea about what could be the cause of my problem?

Here is a video that shows the insides of the player :
Arcam Alpha 5 CD player repair and upgrade - YouTube

Also, what do you guys think about these products :NET Audio
Are these mods worth it? and is it something someone with little experience could attempt on his own?

thanks,
Antoine
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Old 2nd April 2013, 02:20 AM   #2
AMTL is offline AMTL  Canada
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Join Date: Mar 2013
Ok I think I found something.

To track down the faulty part(s) I thought that since it played well when cold, I would bring it up to the temps at which it plays badly and try to cool some parts until I find what makes a difference in sound. So I put some isopropyl alcohol in the freezer and with a q-tip applied some of it alternatively on chips and transistors. It turns out that the tda1541 reacts well. As soon as I cool it, the sounds becomes free of artifacts. I guess that is the faulty part.

I have another player (Micromega Digit with a skipping issue) in which sits a tda1451-s1 (single crown) in a socket so it's really easy to remove. I could install a socket in the Alpha5 and use the S1 from the Micromega I guess? Before I proceed, is there something I should check on the Alpha5 that may have caused the failure of the tda1541? I'd like to keep the S1 alive.
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Old 2nd April 2013, 06:23 AM   #3
josha is offline josha  United Kingdom
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Hi AMTL,

Once you get the socket in the Arcam but before putting the replacement TDA in check that all the voltages are correct on the relevant pins. I'd also check the associated decoupling caps (there should be a large electrolytic and a smaller smd for each of the three supplies). I haven't worked on this player but I'm sure there's a recent (ish) thread on modifying it. It's probably worth tracing the supply's back to the transformer as it's an s1, pretty valuable things those!

I'd also then check the output stage, I don't know what the arcam uses but check for shorts, faulty opamps etc.

Sorry not to be more specific! Hopefully someone with experience of this player will chip in!

Cheers
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Old 2nd April 2013, 08:49 PM   #4
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Default go to it

I have had one of these for 10 years. I did mod it to partial destruction, and learn a lot doing so. I still use it as a transport without the TDA1541. The layout is rather old so while there is lots of space to do your modding, that also limits the effectiveness of those mods. Since the DAC board is easily removed, modding is easier. There are many threads about modding the TDA and the player so have at it. I recall that PS decoupling, clock mods and NOS mods were fairly simple for this player. Watch the heating of both the TDA and the SSAA7220/B, I think I put a heat sink on top of those two chips.

The disk mechanism is almost indestructible, and you can find many places to put blue tack on the unit for damping. Just watch out for getting the blue tack in places that will not interfere with the opening/closing operation.

Have fun
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Old 2nd April 2013, 10:10 PM   #5
pilli is offline pilli  France
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Quote:
Originally Posted by AMTL View Post
It turns out that the tda1541 reacts well. As soon as I cool it, the sounds becomes free of artifacts. I guess that is the faulty part.
For what it's worth:
I think I can confirm that the TDA1541 does have a tendency to produce a lot of heat.
I have a Cambridge DAC and there as well the four TDA1541's have heatsinks glued on them: just a flat bar of alluminium, not very large, you can see a picture here, it's those vertical cards:
Need schematic for a Cambridge Audio CD3 cd Player

I unglued one to see what grade the chips were, and in fact it took off some of the marking with the crown
Since I didn't have the right glue to put it back, it is now just clamped with a washpin, since it is close enough to the PCB edge so that this is possible.
All this to say that if you find a way to fit heatsinks to the DAC, maybe that will do, if it is not yet totally fried. Anyway, do this on the S1!!
Make sure the heatsink doesn't touch the pins (to avoid shorts) and that there is good physical contact with as much chip surface as possible.


-

Last edited by pilli; 2nd April 2013 at 10:13 PM.
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Old 3rd April 2013, 01:20 AM   #6
AMTL is offline AMTL  Canada
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Thanks for the advices,

I tried putting as big a heat sink I could fit. It helped a lot but there is still some distortion after a while, and the heat sink gets real hot. definitely better though. to the point where I think I will test all other components before declaring the TDA dead. I touched the S1 when in operation in the Micromega and it barely gets warm. I'll just make sure it's not something else.
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Old 20th April 2013, 12:44 PM   #7
AMTL is offline AMTL  Canada
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Just an update,
Socketing the tda1541 o nthe Arcam seems to have eliminated my problem. It doesn't get hot anymore and it plays well. All voltages are ok. I must have had a bad solder joint somewhere? or maybe just the fact that it sits higher now, it has more air around it.

Anyway, I changed all electrolytics on the board. This made an appreciable difference in sound (but it's not up to the micromega level yet). I have Wima decoupling caps on their way so I'll change/upgrade those around the DAC chip.
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Old 20th April 2013, 05:01 PM   #8
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Congratulations. Odd that the fault didn't stop the chip working until it overheated. Maybe a poor analogue ground connection made the pin hot? Presumably that's where the current dividers dump their unwanted current.

Anyway, perhaps now it's safe to swap the chips.

One good thing about Arcam is the use of single opamps, allowing optimisation for each of the two audio stages. This is an opportunity to find out exactly what characteristics are desirable in each case.

There are lots of very different opinions about the decoupling caps, and about DEM reclocking. There's not much measurement or description of the difference in audio performance, however, so I guess it's a matter of whatever sounds good to you.


Why is the Micromega skipping?
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Old 21st April 2013, 05:41 PM   #9
AMTL is offline AMTL  Canada
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Join Date: Mar 2013
mmmm, so after many hours of listening where everything was fine, I turn it off. This morning, I start it again and there is no sound coming out! The disc spins and change tracks normally, but there is just no sound.

Also the whole case was pretty hot too for something that as been off for hours. Is this normal? I thought that when the power button was in the off position there was no power anywhere. I opened it and found out that there was voltage coming to the DAC board even with the switch at off. Maybe that is what caused the failure of other components in the first place?

anyway I'm going to try to turn off the muting section, I think it may be why I'm getting no sound.

The Micromega now skips less. I changed a big cap that seemed to have leaked in the power supply section. there is still rare skipping occuring but I think it's a mechanical issue. The unit is a cdm4/19 and there is a plate that sits on top of the cd and on the top of that plate is a bearing that spins on a plastic surface. That surface should be flat but the metal bearing has carved a dip in the plastic. I think that sometimes the bearing gets in or out of that dip and it affects the rotation of the disc. I tried to find a replacement plastic plate (easy to R&R) but have not been able to source the part. anybody knows where to find this?
Thanks,
Antoine
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Old 21st April 2013, 07:44 PM   #10
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The service manual must be free somewhere if you don't have one. It shows no switch in the mains circuit. SW402 switches off the +5V(s) supply, and grounds the reset circuit. You should remember to switch the machine off at the mains.

It looks like the decoder is powered from the (s) supply, whereas the DAC's supply is unswitched, so it might have baked itself to death in the night if the fault reappeared.

It would be strange if this latest failure were a new fault. Before blaming the mute circuit, I would first check the supply voltages to the audio stages, and then for an audio signal at each of the outputs of the first opamps after the DAC.
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