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ALWSR

Disaster has struck. While I was trying to iron out some low level noise on the SEN and then was setting up the Avcc/2 voltage I noticed a drop in the Avvc feed volts and most of the diodes on the ALWSR were out. After some tests it is clear that there is a fault with the Left Channel Avcc input on my (rather elderly) Buffalo II. That left input measures at just 26 ohms load resistance and sinks as much current as my pre shunt reg is able to provide, that's >90ma. In contrast the right channel measures at 120k and sinks around 25 mA. Rather looks like my Buffalo will roam no more (at least not in stereo) as I think the Avcc reg output feeds straight into the ESS9018 chip via an SMD inductor, and I don't think the ESS9018 is user repairable (though it may be replacable). I've posted on the TP forum and expect the bad news to be confirmed soonish.

I've no reason to blame the ALWSR and suspect I have a fault on one of my SENs that has sent excess volts back to the Avcc reg via the Avcc/2 circuit, or that this same Avcc/2 circuit has made the ALWSR go unstable. Both ALWSRs appear fault free but just ran out of juice thanks to their upstream Salas shunt regs.

Anyone got a Buffalo DAC going spare over this side of the pond??

John

(BTW if I don't appear upset it's because I'm still in denial)
 
Oh bugger John my heart truly bleeds for you, sincerely it does.
A post on Patricks thread my also shed some light, I too have had Sen worries for a week or two but just accidentally stumbled on a bad joint, My Sen intermittently stopped drawing current but luckily sorted now.

Why do you need to adjust the Avcc/2? Its just a pair of resistors and not too critical anyway acordingly to the Spice model, unless your running flatout.

A Sabre is not going to be fast in coming, do you have other DACs to use for music which seems the main concern. I could send a crappy DacMajic if your unstuck, its crappy but its music.

Should you be blessed with bags of lolli then buy two new Buffalos, Dual mono is recomended IMO, Tony S also.
 
Thanks for the ideas and sympathy Tony. You've reminded me of my old TP Opus USB receiver board which has an onboard DAC of its own. I'll give that a try while I await replacement(s). In the meantime I could lend you one of my completed ALWSR's to try aginst your Flea as Avcc feed.

John
 
john.luckins said:
Thanks for the ideas and sympathy Tony. You've reminded me of my old TP Opus USB receiver board which has an onboard DAC of its own. I'll give that a try while I await replacement(s). In the meantime I could lend you one of my completed ALWSR's to try aginst your Flea as Avcc feed.

John
Click to expand...

Well mighty kind, I need twins of everything though but probably have all the basics of an ALW so could simply copy.

What a wonderfull community we have here, your in your darkest hours and you think of others.
 
Thats really bad luck John especially when you had it sounding so good.... Had a quick look around on the TP site but they do not appear to publish a schematic for the BII and neither could I track it down elsewhere on the net.
Commiserations.......
I suppose you could replace the Sabre which should be available from Ismosys (that is if it is actually the Sabre that has blown)
I also wanted to make you aware of this vendor and thread......if you are up for a bit of design and SMD work.
http://www.diyaudio.com/forums/vendors-bazaar/225719-es9018-32bit-audio-dac-kit-usd89-95-a.html
 
Thanks for the link Avinash, the photos on that thread and on its links allowed me to confirm the Avcc inputs to the Sabre chip and all the associateed components. There are 4 caps per Avcc channel and one series inductor but sadly none of these are to blame for the low resistance Avcc input, I lifted each to check. The input pins to the Avcc of the chip are themselves faulty. A quick search has found a UK supplier of the ESS9018 chip alone for £46.20. I might have a go at replacing the chip myself and save £200. I've reflowed Sony PS3 chips before and figure that as long as I can remove the old chip cleanly then I should be able to properly position and reflow the new one.

John
 
John....you are probably a dab hand at SMD techniques and have a hot air rework station but fwiw I recently blew a 40 pinner on my Amanero board. I have never worked with SMD before and I am pretty poor at soldering in general. I tried using the enammeled wire technique as shown here.
http://www.youtube.com/watch?v=tlSY1uaw0GA
It wasn't succesful for me as I found that the solder stuck to the pins after the wire had come passed through so I had to repeat a few times. In the process, I managed to lift a few pads so that was that!
I also saw this chipquik product which seemed quite good.
http://www.youtube.com/watch?v=FTQqjggeklo
I went on to their website and registered and they sent me a free small sample pack which I still have and which I could send you if you fancy this method. It came too late for me to save my board. You could also go on their website and register yourself for the free sample. I think it took about 2-3 weeks for the sample to arrive so I am not sure you can wait that long.
I also bought a USB microscope which is great for inspection but not much good whilst you are doing the work as you have to get it quite close to the board so impedes access for working on the board. You can borrow this if you want.
It obviously makes sense not to buy the replacement chip until you have successfully removed the existing one without lifting any pads?
 
Thanks for the tips Avinash.

I fear I'm now going way off subject in this thread so if there's more to post I'll start one devoted to the repair!

I don't have any equipment for or experience of SMD work but there was nothing to lose. I will need a fixed magifying glass for the resoldering as well as an ultra fine tip for my soldering iron but that's all I hope.

I decided that given the ESS9018 chip was toast I would snip its pins and remove the remnants after. This has worked quite well though I did manage to slightly lift one of the pads, funnily enough it happens to be one of the Avcc decoupling pads. Here's a picie of the aftermath.



I'm not sure whether to leave the slightly lifted pad alone and hope the damaged solder resist around it will be enough to keep the resoldered pins each side of this one unconnected to it, or whether to apply a small smear of epoxy beneath and either side of the offending tab and trace by lifting it slightly. The right amount of epoxy could also help hold the pad in situ during the soldering.

A company called Ismosys has the ESS9018 chip in stock and I'm going to pick one up on friday for fitting over the weekend. That's £42 instead of £250 for a new board. I'm a little happier now... as long as it works.

Meanwhile I might make up a modified ALWSR to replace the Vdd-xo 3.3v and give my SENs a thorough MOT.
 
Well good news generally then John, right choice in cutting the dead Sabre first, four sided devices can be a pig to lift.
 
It has taken less than 3 days to remove the old ESS9108 DAC chip, source a replacement and fit it. Here's a picie of the the result:



Not bad for a beginner. My soldering iron tip wan't very good as it was worn , but it was fine enough to do the job. I really could have done with much thinner solder than 0.7mm too but I got away with it. A solder blob found its way behind two adjacent pins and shorted them and it was a little tricky to remove - used a solder sucker in the end. I will be powering it up this evening to see if all is well and then reconnecting the SEN and ALWSR. Fingers crossed.

I think Ismosys, the UK distributor of the ESS parts in the UK deserve credit. I emailed them at about 1:00 in the morning and got a reply from their Managing Director 40 minutes later followed an email re availability at 9:00 in the morning from their Commercial Director. I had the chip in my hands within a day. Quite remarkable service.

Anyway, I'll be fitting an ALWSR to the Vdd-xo input to replace its Trident in the next day or two and am looking forward to seeing how that improves things.

John
 
Well you were sure fast at getting out of that hole. Looks like a machine job, neato.
What did you do with the flaky pad?

EDit
Thats not a Buffalo III?
 
No, you're right Tony, its just a humble Buffalo II. The flaky pad stayed put when I lay the very tiniest amount of epoxy beneath it, the epoxy either side of it also served as a form of solder mask. There was a lot of swearing going on while I was doing the job, especially as my fine soldering iron tip was really not up to the job. The best bit of advice I got was that I should be very sparing with the solder.

I also found a very dodgy Vdd-xo connectionat the header which I've corrected. The caps C1 to C4 are 10uF jobbies and I'm just wondering if they can be improved upon at all.

Never did get to send you the ALWSR to try - just as well as i need it now. When I get my Flea up and running I can send you it to try.

John
 
Looks like you are well on your way to becoming an SMD expert judging by the quality of that work John!
I am also considering powering the clock on my Buffalo24 with its own dedicated regulator but in my case the mod is irreversible as I have to cut a trace and solder on to a bypass SMD capacitor - so not entirely sure about going ahead.... Will wait for feedback from your experiment before I move forward with it.
Best of luck when powering up....doesn't look like you need it as it all looks really clean and tidy from the piccy.....
 
Sorry I seem to have forgot your on Buffalo II, your board did not look like mine.
The epoxy trick is something I will remember, you used 2 part?
All caps can be improved?
Not to worry about the ALWSR, I have plenty to keep me occupied right now, the main thing is one of us tries both. You have Flea parts? You going all tricked out with a Flea?
My Hack is neat with only two track cuts if you need more detail just ask but I rather doubt you'll need it.
If your doing my CCS job I could knock the little daughter board up that drops into the LED pads if it helps.
Depending on how ALW and Flea compare we could also try using a Flea to feed the error amps on the ALW?
 
themystical said:
I am also considering powering the clock on my Buffalo24 with its own dedicated regulator but in my case the mod is irreversible as I have to cut a trace and solder on to a bypass SMD capacitor - so not entirely sure about going ahead....
Click to expand...

All my DAC clocks have benefited from a Flea, no doubt at all.


Also a possible benefit of moving the clock to the Flea board so long as the Flea is close. Clocks are real noisy and pollute everything IME, getting them out off the Buffalo ground plane may be advantageous.

Be good to have Martins input here.
 
Arf. No idea, need to get myself a copy of the ESS datasheet, a Buffalo dac* and have a good look at it - but I'd not remove/relocate that clock lightly. Separate quiet PS feed in is probably a v good idea if it doesn't have one (though I'd be surprised if so)

Well done with the quick fix and heart transplant John - that's impressive! If C1-4 really are 10uF then they are MLCC and I'd leave-be; I'm pretty sure nothing else one could fit/tack-on there will do as well broadband.


(*yep I'm still happily using a cd player)
 
The Buffalo III has seperate clock feeds but not sure of the 0v, maybe that just gets lumped into the main ground plane.

If you kill the feed to the clock on a Buffalo III the clock output goes silly high impeadence, so its as if its not there? Hence easy to test without physically taking the clock out.

On my to try list is to kill the Buffalos clock feed and drag in the WaveIO clock and also maybe try a Tentlabs clock
 
Oh dear john :-( this thread went above my head weeks ago so must admit I stopped reading it so I missed that mishap. Sounds like you're sorted now.

I've done a couple of chips in the past with tips that were miles to big. I put flux on the pads with a flux pen, secured one corner of the chip in place with a big blob of solder. Then used the flux pen to get more flux on the pins and solder resist between the pins. Then get a blob of solder on the iron and draw it across the top of the pins down one side of the chip, slow enough that the flux boils, then repeat each side. Miraculously the solder only flows round the pins/pads, no bridges. If the solder looks a bit heavy handed you can drag the tip back over again, the excess pools on the iron tip. Lastly sort out the corner you fixed at the beginning.

Stefan
 
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