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Cambridge Audio 851D: inside view

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My 851D kicked the bucket recently and it's out of warranty, so I opened it up to see if re-seating connections might fix the channel/static issue, whether there were any terribly obvious issues with caps, solder joints, etc., and, of course, to take some photos.

First look: Nice toroidal transformer, dedicated headphone amp at the bottom. There are two PCB's at the top of the photo. From left to right, the lower PCB has analog outputs (balanced XLR and stacked unbalanced single ended) with dual Analog Devices 1955 directly below the analog outputs, moving to the right: 2 optical and coax inputs/outputs, DAC/DSP section in the middle, some control circuitry (triggers and RS232), and then power on a separate PCB to the far right.
Daughter board has, from left to right: AES/EBU input, BNC input, 2 more optical inputs, USB B, and USB A for Bluetooth, and a trigger.
There's also a vertical PCB at the very bottom for LCD, physical buttons, and volume.

IMG_0711.JPEG


Close up of the lower board analog, DAC, and DSP sections, with the daughter board removed. Wires were in the way here, but I moved them for the next photos:
IMG_0713.JPEG

Rows of nice caps:
IMG_0714.JPEG

IMG_0716.JPEG


Analog and DAC section again, without wires in the way:
IMG_0715.JPEG


Close up of DSP, giant IC:
IMG_0717.JPEG


Dedicated headphone amp PCB:
IMG_0719.JPEG


Power section, dedicated hard switch above the IEC plug:
IMG_0720.JPEG


Daughter board:
IMG_0724.JPEG


Was a little surprised to see this on the bottom of the daughter board. Looking closely, the PCB's are nowhere near as clean as I would expect (dust aside):
IMG_0722.JPEG


Requests, comments, corrections welcomed in replies. Suggestions too. I tested the headphone amp and it has dropped one channel and has static in the other, which is the same as the balanced and unbalanced outputs. Doesn't matter which input is selected. Digital passthrough doesn't have any issue. So I think power is clean and there's a component that gave up the ghost in analog stage... but it could be in the DAC / DSP stage... I haven't seen any schematics for this unit.
 
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OP
R
Joined
May 2, 2020
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My 851D kicked the bucket recently and it's out of warranty, so I opened it up to see if re-seating connections might fix the channel/static issue, whether there were any terribly obvious issues with caps, solder joints, etc., and, of course, to take some photos.

First look: Nice toroidal transformer, dedicated headphone amp at the bottom. There are two PCB's at the top of the photo. From left to right, the lower PCB has analog outputs (balanced XLR and stacked unbalanced single ended) with dual Analog Devices 1955 directly below the analog outputs, moving to the right: 2 optical and coax inputs/outputs, DAC/DSP section in the middle, some control circuitry (triggers and RS232), and then power on a separate PCB to the far right.
Daughter board has, from left to right: AES/EBU input, BNC input, 2 more optical inputs, USB B, and USB A for Bluetooth, and a trigger.
There's also a vertical PCB at the very bottom for LCD, physical buttons, and volume.

View attachment 240851

Close up of the lower board analog, DAC, and DSP sections, with the daughter board removed. Wires were in the way here, but I moved them for the next photos:
View attachment 240852
Rows of nice caps:
View attachment 240853
View attachment 240856

Analog and DAC section again, without wires in the way:
View attachment 240854

Close up of DSP, giant IC:
View attachment 240855

Dedicated headphone amp PCB:
View attachment 240857

Power section, dedicated hard switch above the IEC plug:
View attachment 240858

Daughter board:
View attachment 240859

Was a little surprised to see this on the bottom of the daughter board. Looking closely, the PCB's are nowhere near as clean as I would expect (dust aside):
View attachment 240860

Requests, comments, corrections welcomed in replies. Suggestions too. I tested the headphone amp and it has dropped one channel and has static in the other, which is the same as the balanced and unbalanced outputs. Doesn't matter which input is selected. Digital passthrough doesn't have any issue. So I think power is clean and there's a component that gave up the ghost in analog stage... but it could be in the DAC / DSP stage... I haven't seen any schematics for this unit.
Related forum posts: https://www.diyaudio.com/community/threads/cambridge-audio-851c-problems-and-possibe-repair.338958/
If I can get mine fixed, I will post back an update.
 

voodooless

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3794ADC4-649E-4144-9515-3798462E2371.jpeg
Is it just me, or does this cap look wonky?
 

voodooless

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It looks geometrically proper, some components around it are crooked and so that might give a sense of obliqueness.
Could be, to me, it looks kinda too buldged though, especially compared the twin behind it. Could be an optical illusion though.
 

Doodski

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Could be, to me, it looks kinda too buldged though, especially compared the twin behind it. Could be an optical illusion though.
It could be the reflection of the red/orange capacitors beside them. The reflection on the nearer electrolytic cap is pretty rounded.
 
OP
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I took out a real camera and a 100mm macro lens to get some better shots. I think it is reflection/perspective that made it look weird in the first photos, I did a double take when @voodooless pointed it out. Here's the macro close ups:

a) top in focus
_MG_5263.JPG


b) bottom in focus. Still lots of reflection though, it's tough to get a shot otherwise
_MG_5264.JPG


c) For comparison, from further away, other side (not the same caps)
_MG_5257.JPG


I ran out of air dusters, otherwise I'd blow away the dust for the photos.

Edit: I got a better angle and took one more photo. It does look different from the others:
IMG_0733.JPEG
 
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voodooless

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Looks fine on those pictures indeed.
 
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