Soundcard PCB layout and layers ? - Page 1
Forum section: electronics / projects

author: MathWizard
author_rank: Super Contributor
timestamp: March 24, 2020, 08:08:56 pm
content: I have an old soundcard here that used to have an intermittent distortion problem of some kind. It's full of caps, I'll have to check some of them later. Also at some point a little fuse on the 12V input got fried, IDK if it was me or while in the PC.Today I'm going through datasheets for it. I just want too play around with it, see if I can find the cause and fix it, and then see what a BusPirate makes of it. See if I can "hack it up" (LOL I bet kool kids say that)1) It's PCI-e x1, has digital audio in/out, and 7.1ch output. How many layers would such a thing be? I see the #6,8, even 10 ?Here's some spec'shttps://www.guru3d.com/articles-pages/auzentech-x-fi-forte-7-1-soundcard-review-|-test,3.htmlThere are via's everywhere, linear regulators on the top, with little else. On the bottom there's all the digital chips, buck converters, op-amps, output caps/etc2) And in the end, what about the chips on it like the this 24-bit 192 kHz Stereo ADChttps://www.cirrus.com/pubs/proDatasheet/WM8782_v4.8.pdfI don't really have any ADC, how general purpose is such a thing ? If your voltages and frequency are close to audio properties, I bet someone could do a lot with it. I have a lot of analog stuff to learn 1st tho. But I can't wait to start trying something with ADC's and ram chips, etc

author: Whales
author_rank: Super Contributor
timestamp: March 24, 2020, 10:22:23 pm
content: Depends what you mean by "intermittent distortion".Distortion that cuts in and out arbitrarily?Likely to be a bad connection somewhere. Parts within the soundcard, connectors to the outstide world or in the outside world (speakers, cables, etc). EDIT: pay attention to the grounding jumper on the corner of the card too.Distortion that's always there anddoes notsound like clipping: could be the caps. EDIT: the caps are an unlikely cause of problems in general unless this card has been run in a hot environment for a long period of time.Extra noise that's always there, even when sound is not playing?Not distortion, instead that's interference from other components.You need to be able to reproduce the problem if you want to get to the cause, otherwise you will have to remake half the card (and still may not fix the problem).

author: Whales
author_rank: Super Contributor
timestamp: March 24, 2020, 10:28:40 pm
content: To answer your questions:Layers: probably not more than 4. There's no need for super-high density in an audio card, not worth the cost unless you need it.ADC: yes ADCs are used a lot beyond just audio cards. It looks like this one supports I2S, a simple and standard interface.Be wary however that the "24 bit" claim is not necessarily valid in practice, most often the last several bits are not visible/useful/distinguishable form noise or other forms of error. Also the card might only be useful for AC coupled operation (have not had a proper look, but I saw mention of internal amplifiers).

author: MathWizard
author_rank: Super Contributor
timestamp: March 24, 2020, 11:29:57 pm
content: This had distortion year's ago, I don't remember exactly how it would start, or how often, maybe a few times a month?I want to say I fried the fuse trying to power it up out of the PC, but IDK, I should remember either situation, since I'm good like that. So far I've only found the 12V rail on the linear reg. side. No sign of any damage tho. I have a bench PSU, at some point I want to power up the soundcard w/o the PC.I tried counting the layers with a microscope, but I'm not used to multy-L PCBs at all, so IDK.It only has +12 and 3.3V in from the mobo. I need to continue with the datasheet searches.

author: magic
author_rank: Super Contributor
timestamp: March 25, 2020, 05:50:27 pm
content: Quote from: MathWizard on March 24, 2020, 11:29:57 pmWhat would be the point of that? You aren't going to interface anything easily with PCIe anyway.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 25, 2020, 10:36:45 pm
content: Quote from: magic on March 25, 2020, 05:50:27 pmQuite a few embedded ARM platforms have PCIe.

author: MathWizard
author_rank: Super Contributor
timestamp: March 27, 2020, 11:32:47 pm
content: Quote from: magic on March 25, 2020, 05:50:27 pmWell I'm not sure it's fried or it. So far I mapped out a lot of the schematic. Seems good, checked a lot of caps w/ LCR meter, nothing stand's out.I found thisR3112Q282CRicohSC-88AVoltage detector IC2.8V±2%, -Reset ODOTook me a while to figure out what it was in circuit, on the output of the 1V step-down converter. Now it makes sense.I can't find a datasheet tho, anyone know the name of something in LTspice like those ?As for the distortion I remember, if it was an transistor radio, I'd say the distortion was not at the input stage. But was getting digitized somewhere, making distorted/computery sounds from the speaker, as opposed to a sound like static on the output, or mains humAs for the digital of what this thing does, it's 99% new to me. What all can I do powering this thing off PSU, and using an AWG ? I know the CPU won't want to do much like that, but I mean for checking the op-amps, and looking around for fun.I just brought up the PC to test it in, my BusPirate is under CV lockdown at the post-office, what else can I try. What programs can talk to a soundcard on PC and tell me exactly what's up? I have diff.probes if I want to go probing the card in the PC.I will learn all this stuff over the next few years (unless some major changes)

author: Whales
author_rank: Super Contributor
timestamp: March 28, 2020, 07:58:39 am
content: QuoteThat sounds like an unusually strong effect from digital interference (emitted by other parts of your computer). There will always be aminoramount of digital noise being picked up by your sound card -- try turning an external amplifier all the way up and "listen" to what silence from your computer's sound card is like, especially when scrolling pages in a web browser or running other software.If it's coming in seldom and noticeable bursts then it suggests something in the analog parts of the soundcard PCB is going (temporarily) open circuit. Bad solder joint (eg cracked) or connector are some likely options.QuoteNothing. Sound cards do not self-diagnose. If you're lucky there might be JTAG or some other debug interface, but that probably won't help here (your fault sounds like an analog problem not a digital one) and it would take a lot of reading + reverse engineering before it would be of any use.Regardless: if you can't recreate the problem then you won't be able to fix it. I would suggest running the card in a computer/motherboard you don't care too much about and then start gently physically stressing parts of the card. ie listen to what comes out of your speakers whilst you flex the card gently with your hands, cool the card, heat the card, etc.If you want to go hardcore then you can order a PCI or PCIE extension cable so the card can be on your bench whilst you work on it (and this also allows you to cut certain traces), but it's not worth going into the complex end of debugging until you first check the simper stuff.

author: magic
author_rank: Super Contributor
timestamp: March 28, 2020, 08:11:16 am
content: I have never seen a JTAG header on any computer component, ever.Quote from: Whales on March 28, 2020, 07:58:39 amYep, that kind of crap usually is there but it's mostly constant.Anything intermittent is most likely software

author: Whales
author_rank: Super Contributor
timestamp: March 28, 2020, 09:37:55 am
content: Quote from: magic on March 28, 2020, 08:11:16 amNo no, software is consistent in its unreliabilityCould also be possible. Eg wrong bitlength PCM streams, all sorts of stuff. I've read stories about addon sound cards having weird driver-related reliability issues. Would be horrible to debug.

author: MathWizard
author_rank: Super Contributor
timestamp: March 31, 2020, 11:43:53 am
content: For the dual audio rail output's , it uses this LM2735 SEPIC DC-DC regulator. I' not familiar with SEPIC layouts. In the data sheethttp://www.ti.com/lit/an/snva255a/snva255a.pdfI don't see this type with split rails. (see attached schem. that I've mapped out)And I I tried it with a mosfet stand in for the non-functional LT chip, IDK if it's really working, maybe I'm missing a hidden part tooI can't find an L.Tech. equiv. of the LM chip either