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Teardown of Anthem MRX 520 AVR

amirm

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#1
This is a teardown of the Anthem MRX 520 Home Theater Receiver (AVR). I already reviewed the MRX 520. With kind permission of the owner, I took the lid off it and took some shots. Alas, the boards are tightly stacked on top of each other and I don't want to remove them in the odd chance that something happens to them. So this is not a very detailed teardown.

Here is a shot of the unit (click on the image for larger size):

Anthem MRX 520 teardown Main Components.jpg


Overall, it is a very clean assembly. There is EMI filtering and such on the AC terminals, etc. A few issues though:

1. HDMI uses a parallel set of differential lines and a clock. The standard assumes that the timing and hence lengths of each of these parallel connections are identical. Otherwise the clock can "skew" relative to them causing data recovery issue. What this means is that when you look at the HDMI transceiver chip, all traces from it to the connector must be equal length. They are that for HDMI 1 and 2 inputs. But if you look at the traces for HDMI 3 input, the inner traces that make the 90 degree bend are by definition shorter than the outer ones. Given the speed of HDMI these days with 4K, high frame rate and color depth, this becomes doubly important.

This is a common problem with AVRs. But doesn't excuse the fact that it can cause compatibility issues with other devices. So if you are using HDMI 3 and having trouble, switch to the other inputs and see if the problem goes away.

Someone was clever with using a PCB as a bracket to hold that ribbon cable that communicates with the front panel. PCB can be cheap to build so may have been cheaper than using a clip of sorts. Problem is, even with all the slots in it, it will impede convection flow.

There is forced fan cooling as you see. The fan however should be placed on top or below the fins as they have much more surface area to cool them. Still, once that fan kicks in, it will provide far more cooling than you would get with convection alone.

I also like to see the fan farther away from interference point of view. And putting it on top like Pioneer does will do that.

The fan by the way is a brushless 12 volt DC unit by Xfan (used for computers and such). So you have options to change it to something else.

The analog board seems to use high-quality Elna capacitors:
Anthem MRX 520 teardown Elna Caps.jpg


Here are the beefy output transistors:


Anthem MRX 520 teardown Output transistors.jpg


They are the Sanken 2SB1647 and 2SD2560 darlington transistor pairs. Darlington configuration is a quick way to get high gain.

That's it really. I still have the unit open so shout if you want to see something else in the next couple of hours. :)
 

amirm

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#2
I forgot to mention: I don't see evidence of them OEMing the HDMI board from someone else. They seem similar to the rest of the PCBs so it is likely an inhouse design.
 

GrimSurfer

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#3
Interesting to see it uses a few AVM 60 boards. Spreads the cost of in house design/manufacturing I guess.
 

Icboschert

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#4
Is it possible to disconnect the fan and still power on the unit, then run tests? Just trying to understand how much the fan affects SINAD and if that can be tested. Not asking for the test to be done but theoretically.
 

GrimSurfer

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#6
Do you condition units before your test to bring them up to full operating temp?
 

amirm

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#7
If you mean FTC style (1/8 power for 30 minutes of whatever it is), no. I do let them warm up for a few minutes though for the dashboard. For AVRs it takes even longer after I go through setup and such. With one exception, warm up has never had any effect anyway.
 

GrimSurfer

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#8
Good to know. Your method would likely give most gear a very good opportunity to measure as well as possible.

As an aside, it would be interesting to learn of any additional distortion when the fan is active (either from the fan itself or a byproduct of heat). Not nit-picking about your methods here, as you are delivering performance figures that manufacturers are either too lazy or too ashamed to release!

Well done!
 

amirm

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#9
I have a policy to not put amplifiers too hard as I already damaged one that way. So I don't think I can make it hot enough for the fan to come on. If this were my own unit and didn't cost much, I would do that. But can't take chances with other people's gear, especially when they cost so much.
 
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#10
I wish you did more lid-opening.
Sometimes it is meaningless but it can still be revealing, imo.
I understand that it's not your gear but I think most would trust you to take lid off for a peek.
 
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#11
I would have thought that fan would be better placed to blow on the heatsink fins, but then I wondered if they're trying to draw air across the various boards as well? From what I can see, it does look as though three boards are sandwiched there, so I guess heat build up could be an issue.
EDIT: @amirm A quick Google suggests the maximum signalling clock rate for 4K is just short of 600MHz.
The wavelength at 600MHz is 0.5M - 1/4 wave is 12.5CM so do you think those different length PCB tracks could cause any issue?
I'm guessing (it's difficult to gauge from the image) that the longest track is about 5CM?
 
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