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pcm2704 USB DAC chip faulty?
pcm2704 USB DAC chip faulty?
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Old 30th December 2017, 02:03 PM   #1
dj_holmes is offline dj_holmes  United Kingdom
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Default pcm2704 USB DAC chip faulty?

Hello,

I got this cheap DAC but the USB is not working. When I connect it the computers says USB not recognised. My first impression was the connector is faulty but its not. I tried to look for anything broken but its not. The cable and connector is fine. Everything seems to point to the pcm2704. Has anyone got any pointers to testing this chip if it is faulty or not? Thank you
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Old 30th December 2017, 02:48 PM   #2
percival007 is offline percival007  England
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That looks like a Project DAC.
The PCM 2704 is, as far as I know plug and play not needing any drivers for Windows (I don't know for MACs) so it does point to it being faulty or an associated component.

Is the Crystal running? Does it have it's supply on all the correct pins?
The Datasheet is freely available on-line so look at that and do some measurements and get back to us.

Cheers,

P.
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Old 30th December 2017, 03:03 PM   #3
dj_holmes is offline dj_holmes  United Kingdom
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Hi P,

Yes it is a project DAC!

I measured the voltage on the crystal and looking at photo I put ground to the screw and left side of crystal measured 3.4 volts and other side was 1.7v

Sorry what datasheet is available? I did think about measuring the voltage on the chip but I'm a bit lost at understanding it.
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Old 30th December 2017, 03:04 PM   #4
dj_holmes is offline dj_holmes  United Kingdom
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but would the crystal even matter if the drivers failed to install?
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Old 31st December 2017, 05:53 PM   #5
percival007 is offline percival007  England
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Well there's a DC Voltage across the XTAL so you'd think it may be oscillating? Do you have a 'scope though?

If the Drivers are in the CHip though (?) then the XTAL would have to be oscillating for the Chip to work and send them to a PC. If that's how it works. I'm no computer expert.

Google ''PCM2704 Datasheet'' and................................
PCM2704 pdf, PCM2704 description, PCM2704 datasheets, PCM2704 view ::: ALLDATASHEET :::

P.
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Old 2nd January 2018, 01:45 AM   #6
dj_holmes is offline dj_holmes  United Kingdom
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I'm stuck too. I do have an oscilloscope it's the DIY kit version for 25. It works just don't know how to use it.
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Old 2nd January 2018, 09:43 PM   #7
dj_holmes is offline dj_holmes  United Kingdom
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I have one of these I built. Seems to work fine. There is 2 test point on the chip. Can I test this using the oscilloscope?

YouTube
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Old 3rd January 2018, 06:53 AM   #8
percival007 is offline percival007  England
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Quote:
Originally Posted by dj_holmes View Post
I'm stuck too. I do have an oscilloscope it's the DIY kit version for 25. It works just don't know how to use it.
I think find an item that works (CD, Tuner, anything) and have a scope around to get yourself familiar with the workings of your scope.
Then have a look at the Datasheet for the 2704 and check all the relevant points.

Does the unit work as a DAC for Optical and Coax?

The PCM 2704 is readily available.............5PCS PCM2704DB PCM2704 PCM2704DBR Stereo DAC +USB+ S/PDIF Brand New CF | eBay

P.
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Old 3rd January 2018, 10:44 PM   #9
dj_holmes is offline dj_holmes  United Kingdom
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Yes rest of DAC works fine.

I wouldn't know what I'm looking for on the scope to be honest
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Old 4th January 2018, 06:57 AM   #10
percival007 is offline percival007  England
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So when you plug it in to the PC (Windows?) what exactly does it say?
Your first post says ''....When I connect it the computers says USB not recognised...''
Do we take it from this the PC knows it has something connected but doesn't know what it is? Or does nothing happen at all?
If (Windows?) you select the 'Speaker' icon down the bottom right and right click, select Playback Devices then plug the DAC in what happens?

You're not going to fix this with just a Voltmeter I'm afraid so do teach yourself how to use your scope.
Google ''How to use an oscilloscope'' and have a read....
how to use an oscilloscope - Google Search

Have you looked at the Link for the chips on ebay? If you're not going to scope anything then just change the chip and see if that helps. If it does....great. If it doesn't then you're only down a Tenner and you can move past this chip. At that point though it will probably be a control problem (?). There's no info available from Project on these and they're 'only' about 80 so you're going to have to knock it on the head at some point.

P.
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