DAC board repair nightmare - Page 1
Forum section: electronics / repair

author: tony359
author_rank: Frequent Contributor
timestamp: September 19, 2025, 05:33:35 pm
content: Hi there,I hope someone can help me in fixing a DAC board of a DTS cinema processor. If I understand right, the board gets digital signal which is converted by 5 DACs (10 channels). There is an e-pot to set the channel level via front panel, a solid state relay to enable/disable the output and then an unbalanced output.DACs are PCM1716Eop-amp are OPA 2134epot are DS1867-10You can clearly see the channel pairs in a horizontal layout on the below picture. You can see DAC, op-amp, e-pot, 2xop-amp. On the right, the solid state relays.(click to see HD version)Some weeks ago I discovered a huge noise out of the centre channel. I was like a continuous "clicking" noise. I "fixed" it by swapping the relevant e-pot but since then, I have a similar noise - just very faint - on the very same channel plus the surrounds. On a spectrum analyser this results in the noise floor of the channel "jumping".I compared with another board I have only to find the same issue on that board.I am 100% sure the issue was not present on the first boardbecause I did record the noise floor with my spectrum analyser just the day before and it was linear. No jumping.https://1drv.ms/v/c/0f215fbb023f1ee9/Ea00uqwU3R1AhEXY8v-hMUABXbjaGNML8LfVkPuFU-xlMw?e=uQl0ePWhile looking for that noise, I found that the e-pots receive configuration data more or less every second and the data frequency matches the clicking noise I see/hear on some channels. I thought that maybe that was my issue: why sending e-pot configuration every second? But no, I have confirmed that other units are receiving the same signal.I swapped the e-pots again, swapped them around but the issue seems to stay on those channels. I swapped all the bypass caps on that channel pair (Centre and Subwoofer) but nothing.I then swapped the op-amp on that channel and initially the issue was even worse. Then I realised that the noise is heavily susceptible to heat. If I heat the Centre/LFE e-pot, the noise on the centre channel increases massively. If I heat the, say, Left channel e-pot, nothing happens. I am pretty confident it's not something around the e-pot as I tried spraying freezing spray on a cotton but which I then put on the e-pot, to avoid affecting other components, and the noise reduced or disappeared.https://1drv.ms/v/c/0f215fbb023f1ee9/EQlEAl6GaBhPt67YOajJTQUBbff66DNixnnTCSb0ShvADQ?e=2VQoHUIf I inspect a recording of those 8 channels, I see that the noise is on all channels. But the affected channels read a different waveform which I guess end up in the audible spectrum.So I feel that a little "clicking noise" is within the design of this unit (don't ask me why) but for some reason, my output board(s) exhibit a louder noise on some channels.Because the noise is pretty low, it is difficult to diagnose with an oscilloscope, it gets lost within the noise floor.Does anybody have any hint please, I am really lost here.PS: the 2.6KHz should be an unavoidable "idle" noise of the old DAC's used.Thanks!

author: Swake
author_rank: Frequent Contributor
timestamp: September 23, 2025, 09:06:31 am
content: So the goal is to find the source of the noise. Here some ideas:Can the origin of the noise come from the digital source signal? I'd try feeding it with a digital 'test' signal. One channel at a time.You should be able to scope the 'noise' in the signal. It is audio level, should not be all that difficult. Ensure to have good ground near the measured signal, not 20 cm further. Us the alligator clip that comes with the probe (or another piece of wire you attach in that place).You swapped the e-pot chips and the noise did not swap? That is not consistent with the freezing spray results. Of course thermal issues are tricky to identify and it can play games with you.Try replacing the chip with a real 10 kOhm pot. Temporarily of course.

author: tony359
author_rank: Frequent Contributor
timestamp: September 23, 2025, 05:47:44 pm
content: I like the idea of the 10K pot - thanks!Thanks for the inputs. The noise is VERY mild so it's difficult to track even with proper grounding.Today I've done another test and the outcome doesn't make sense. Or it does but I'm puzzled.Since my L/R channels were 100% unaffected (no noise, no changes with heat), I swapped the e-pots between L/R and C/LFE.Result: now L is affected by the noise but C is ALSO affected, in a smaller measure. Most importantly, now BOTH channels are susceptible to heat.So I swapped them again between themselves.Result: Both L and C are showing noise, L in a smaller measure. And both channels are susceptible to heat.So it looks like those ICs are damaged by heat? The L/R e-pot was one of the originals.I don't think I overheated anything. I used low melt solder and a soldering iron to remove them, it didn't take more than 15/20s. I soldered them back manually with a small tip, leg by leg. I have some brand new ones which I only soldered using a soldering iron so no overheating possible there - though those chips come from Ebay, the one and only source available worldwide of that package.I mean, it's pretty clear that the noise is introduced by the e-pots. But now I don't really know what to do?I will definitely try the physical pot test but I am pretty confident the issue will have gone then.I have some slightly larger package of those e-pots, maybe I can try adapting one chip and see if it's better?This has been a time vampire you have no idea!Thanks a lot for your inputs so far.

author: Swake
author_rank: Frequent Contributor
timestamp: September 23, 2025, 06:54:36 pm
content: The datasheet calls for:ABSOLUTE MAXIMUM RATINGS Soldering Temperature 260°C for 10 secondsThis is their guarantee of course, in reality it should have a big margin above that. Your experience shows something different however. It might become more fragile due to aging.Are the Ebay chips 'new' or are these refurbished (=unsoldered and cleaned)?There might be compatible digital pot chips on the market. Eventually with an adapter board if the pinout is different.

author: tony359
author_rank: Frequent Contributor
timestamp: September 23, 2025, 07:01:30 pm
content: I'd imagine the "260C for 10s" is more or less the same figure for most ICs, as you say it's the guaranteed values. The ones from Ebay didn't go through that though. They look brand new, in a tape.I've searched everywhere, those chips are only available in 16 pins, mine are 20 pins. Only ONE seller in the USA has them. I paid them an arm and a leg in shipping to have some here.The pads are larger than needed, let me explore the idea of adapting the 16pin ones I have. I could make a small PCB to make things more elegant thought I doubt it can be done elegantly.

author: Swake
author_rank: Frequent Contributor
timestamp: September 23, 2025, 07:03:16 pm
content: btw, the pinout of the 20pin TSSOP on your PCB has 2 more unused pins on each side compared to the 16-pin SOIC version. This means you can not use a 1 for 1 adapter board would these exist, unless you adapt it somewhat.Designing your own adapter board is certainly a good idea.

author: tony359
author_rank: Frequent Contributor
timestamp: September 23, 2025, 09:10:34 pm
content: the problem is that I don't think it's going to work - see attachmentI think I asked already on this forum for an alternative but never got a reply. I'll look further - if you have any ideas, I'm all ears.

author: Vicus
author_rank: Regular Contributor
timestamp: September 23, 2025, 09:25:53 pm
content: UTsource seems to have it in stock.

author: tony359
author_rank: Frequent Contributor
timestamp: September 24, 2025, 04:49:02 pm
content: ThanksI did check some weeks ago and there were none, interesting. I also sent en enquiry to a potential seller but they came back to me with a negative answer.I guess I can try some from them for sure.Thanks!

author: tony359
author_rank: Frequent Contributor
timestamp: September 25, 2025, 05:16:58 pm
content: I've placed an order for some ICs on UTSource, much cheaper than the ones I bought from the US. Fingers crossed now. I'll keep you posted.

author: Swake
author_rank: Frequent Contributor
timestamp: September 25, 2025, 06:17:14 pm
content: Good find. Keep us posted, am curious

author: tony359
author_rank: Frequent Contributor
timestamp: October 09, 2025, 07:54:50 pm
content: I've received the ICs.Unfortunately they are all corroded, they show blue stuff on the legs, all 20 of them. I am going to ask for a refund but I installed one just as a test.Again, no hot air, I soldered the legs one by one with a C210 tip. I'm not touching each leg for more than a second.This is loud, I have loud popping noise from both channels that go through this IC.I struggle to believe that they are ALL faulty the same way - or that they all fail the same way with age. I have ordered some of the nearby resistors to swap "just in case". This doesn't make much sense. My guts feelings say I'm missing something.

author: Swake
author_rank: Frequent Contributor
timestamp: October 09, 2025, 08:17:09 pm
content: Green oxidation might be copper. The legs might be tin (or some alloy) plated copper, and now some of the tin is gone.Let's assume for a moment your chips are all ok, then the question is what else can it be?Power supply? Or something that interferes with it such as capacitors, the electrolytic capacitors but also the other ceramic types?Have you been able to replace one of those chips with a real 10 kOhm pot? Just to exclude the chip as origin of the noise.

author: tony359
author_rank: Frequent Contributor
timestamp: October 09, 2025, 10:15:11 pm
content: When I see oxidation where the package is, it probably means there is corrosion inside the package itself. So I wouldn't trust them.But yes, let's assume for a moment that this is not an issue. Why now I have loud popping noise - which is in sync with the e-pot getting the data, this is not new, it's just louder than the others. This is why I originally replaced the chip, it started making this loud popping noise every second.I haven't tested the fixed resistor/potentiometer, I wanted to test these chips first.I think next is to test the fixed resistor and if it works, try adapting the larger package. It won't look pretty but it's doable.Yes, I completely understand this doesn't make sense though.

author: aeg
author_rank: Regular Contributor
timestamp: October 09, 2025, 10:42:15 pm
content: This is the DTS-XD10 that you've already determined has a poorly designed DAC board, right? Is it equipped with the digital out? Maybe you'd be better off using an outboard DAC.

author: tony359
author_rank: Frequent Contributor
timestamp: October 10, 2025, 06:18:11 am
content: It is - but digital out is an option card which can’t be sourced anymore.Also, cinemas might not have digital input capabilities or might want to keep the XD10 wired in their old film system which definitely didn’t have AES input.I definitely would like to find a solution to this. Then of course the digital output would be the best option.

author: magic
author_rank: Super Contributor
timestamp: October 10, 2025, 06:31:08 am
content: Did you end up confirming for sure with resistors/analog pots that the issue is with individual digital pots alone?Beware that parts from sources like eBay may not only be recycled, but also defective from the factory or even different parts in the same package with fake markings.

author: tony359
author_rank: Frequent Contributor
timestamp: October 10, 2025, 11:51:42 am
content: Quote from: magic on October 10, 2025, 06:31:08 amNot yet. it's going to be the next step. Though if I remove the e-pot the noise goes away. Also when I swapped e-pots around, the issue "moved with the e-pot" though the working e-pot I used on a different channel than failed as all the others when I put it back on where it came from.QuoteI am very well aware of that but this is long discontinued unfortunately so there is no alternative. The above is from UTSource BTW. It was sold as new.

author: tony359
author_rank: Frequent Contributor
timestamp: October 10, 2025, 05:01:33 pm
content: I've now installed a 5K trimpot - I didn't have 10K but turns out to be ok to get to "0dB" level.It works. Zero noise. The LFE channel - which is now "floating", that is, not connected to anything (the e-pots are 2 channels), picks up lots of noise INCLUDING some low level "thump thump thump" with the same period of the serial data to the e-pots. I'd imagine that sending 5V peak to peak around the PCB where low level analogue sound is, was not a good idea.So I guess this confirms that ALL my e-pots are faulty? I'd imagine this is a common flaw which comes up with age and there is no point in sourcing more of them.Options:1. Replace the e-pots with trimpots or fixed resistors. To be honest, those players shouldn't have a level adjustment. The level should be set to 0dB and that's it. It's a "nice to have" but I honestly feel we could live without it.2. Adapt the larger package to the footprint with some flying leads. I can only hope that the larger brother might be immune from this issue? Who knows.Given that I see the noise on working unit - it's just inaudible - I'd be tempted to get rid of the e-pots proactively. The e-pot I originally replaced showed some background noise, not a lot. The replacement (from a working unit) badly failed after a month. Even if I found good chips, I have a feeling those are all going to fail soon. Chances are they all have but the noise is not really audible in a busy cinema so nobody has noticed.Thoughts?

author: Swake
author_rank: Frequent Contributor
timestamp: October 10, 2025, 06:18:58 pm
content: It is possible these are all dead but..... either these have a serious flaw (RIFA cap like) or that is a hell of a coincidence.Don't give up yet... Restart the search from 'point zero' and also search elsewhere. What you have found might be a consequence of something else that is only audible in this combination. Plenty of other stuff can cause trouble.Some ideas in no particular order:- Check for (near) shorts in the digital path near those d-pot and the DAC these are connected to. Check for lines that stay high or low all the time while you'd expect some action on them. Or on the contrary a stable signal while it is floating.- Breadboard them to an arduino or similar and check the d-pots are regulating correctly as expected. Simulate and measure all 256 positions. Put another analog signal trough them and check for the noise.- Check quality of the power supplied to the board and the chips in particular (and especially under load).- Scope the analog 'noise' on the chips and follow its path. Find were it originates, see if you can influence it somehow (finger touching the chip, pressing down on the chip, magnet, ...).- System clock and x-tal. Frequency, stability, pulses missing, strength of signal, width of pulses. Check near the d-pots, the DACs and also near the ASP.- Abuse the reset lines and force reset on the DAC and d-pots after power on, see if that influences things.- Buffer chips on the in or output.

author: linux-works
author_rank: Super Contributor
timestamp: October 10, 2025, 08:48:37 pm
content: if i2c, try an isolator?

author: tony359
author_rank: Frequent Contributor
timestamp: October 10, 2025, 09:27:40 pm
content: It's "serial", unfortunately, which prevents me from installing anything newer I understand. Would you think that something on the serial line might help?I strongly believe that this constant "sending you the data" is a bug which was never fixed before DTS stopped developing the unit. I cannot see a reason for that data to be sent once every second, continuously. When the channel level is changed, EXTRA data is being sent.Unfortunately, I cannot change that.Some time ago I tested by severing the serial line and all the noise disappeared - but I couldn't control the levels anymore. Maybe that could be the solution: a switch somewhere at the back to "enable/disable" level control?@SwakeThanks.The issue is that I now have a number of 2-ch lines showing that noise which started only when I fiddled with the e-pots. If you remember, I had one line (L and R) which was totally quiet, I moved that e-pot to the C+LFE section and it became noisy, not much but a bit. When I moved the e-pot back to L+R it stayed noisy. I didn't use hot air, I used low melt solder. Cannot be more gentle than that.Everything is pointing at those chips. One one line I replaced almost everything: op-amps, capacitors. I have some more components to swap but I think I am wasting my time.The noise greatly increase with hot air on the e-pot and DISAPPEARS with cold spray. Ah: if memory serves the noise goes away if I move the level from 0dB (on the display) to +/- 6dB, the max I can adjust. How weird is that.Let's not forget something: there is NO reason to send the e-pot data once every second. I suspect that that noise is "by design". It's faint (unless I have a "very bad chip") and would only happen when someone is adjusting the level.I'm dealing with another sound device which has different e-pots: changing the level will make some clicking noise but who cares, it's the internal levels and they're only adjusted during setup so they can be a bit noisy and nobody would care.To clarify, the levels for this unit, the XD10, are to be used during installation. I suspect the level of one of those units would be touched between zero and 3 times in its lifeThanks for all the inputs so far.The next step would be to adapt the larger package and see how it behaves.

author: erkko
author_rank: Contributor
timestamp: October 11, 2025, 04:55:21 am
content: Havent been following this saga in detail, but if some non-fixable element is sending data every second and like you say it is rare to even change these levels... and you mention severing that line made it very nice and noise-free. Why not simply add a switch to these lines. Switch the line on when you need to change it, switch it off when done. Just guessing.

author: tony359
author_rank: Frequent Contributor
timestamp: October 11, 2025, 09:44:12 am
content: Indeed - I mentioned that idea on the post just above! (I don't mean to sound aggressive of course, I appreciate not everybody have time to read everything, just to say I had that idea just yesterday).

author: tony359
author_rank: Frequent Contributor
timestamp: October 11, 2025, 03:43:44 pm
content: larger package is up.The issue is still there! 😀 Which is impossible. I also tested the channel level from the software and it works so the chip is correctly wired.I'm at a loss. I cannot possibly believe that all those chips are defective all in the same way. But I also cannot believe that suddenly two different boards and multiple channels started showing similar issues after I fiddled with those e-pots.I need a hug.--- After the hugI went back to the board and fitted the switch on the potentiometer configuration line. My concern was that with NO data, the "reset" line would still instruct the IC to get the configuration data from the - now floating - line.Which is exactly what happened. With the switch off my levels drop in level and when I switch it back on, they all go back to the settings the logic is sending.But what about the noise?Well. It's gone. From all channels. With the switchEITHER ON OR OFF!! What the heck??? I started the player with the switch OFF so I thought maybe it's a timing issue of some sort.So I power cycled the unit with the switch ON.STILL NO NOISE.I turned on the scope, maybe the pulses had gone - no, they're still there. On the RTA I see "jumping" around 20KHz and the vu-meters are also slightly jumping. That, in my limited understanding, is the behaviour of a healthy unit: the noise is there but basically inaudible. The other spikes you see are the CPU/PSU fans, please ignore them.So what fixed my board? All I did was to cut a small section of a trace and pull out a couple of wires and a switch.

author: erkko
author_rank: Contributor
timestamp: October 11, 2025, 04:20:39 pm
content: Quote from: tony359 on October 11, 2025, 09:44:12 amYes you did, my mistake.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 11, 2025, 04:51:44 pm
content: What about the supply rails? Maybe your problem is some regulator, or dry caps?

author: Swake
author_rank: Frequent Contributor
timestamp: October 11, 2025, 06:31:47 pm
content: Quote from: tony359 on October 11, 2025, 03:43:44 pmLiterally. It stands out. You have a bugAnd you have good news. Not yet an eureka moment but you're not far away.The issue is something common to all channels.Don't remove the switch, but bridge it with a piece of wire to confirm the switch is not what solved the noise issue. If you have the noise again, well... spookyThere might be a physical issue like a pin on some component that is loose, cold solder, something like that.

author: tony359
author_rank: Frequent Contributor
timestamp: October 11, 2025, 07:37:18 pm
content: QuoteYes though... I had unaffected channels which became affected when I started fiddling with the e-pot.QuoteI see the logic but... on two different boards, which used to work fine?Sorry, I don't mean to sound harsh, it's just that nothing here is logic at all! But of course you are right.I've checked the board under the microscope umpteen times, cooled down all chips, warmed it up.Voltage regulators could be an idea (one system is fully re-capped with new PSU, the other has only the MB recapped) though I still don't get why the noise would then follow the data burst for the e-pots.Trying to follow some logic: the board was noisy. Then it wasn't. What happened in between? I REMOVED the board, fitted the switch, put the board back.I think I'll check the two ribbon cables which go to the board. I'm thinking of some grounding issues, I know for experience that those crimped ribbons can get bad. It just takes a little oxidation and they start causing all sort of weird issues.And yes, I will jump the switch to confirm - thanks for the tip.My guts feeling is that next time I power on that possessed machine, it'll be noisy again! 😀

author: coppercone2
author_rank: Super Contributor
timestamp: October 12, 2025, 04:24:49 am
content: are you sure some shit like a via is not cracked and every time you do something it gets like disturbed to a slightly better or worse bad contact?a cracked cap, trace, via, connector, etc.When a bunch of parts all do the wrong thing chances are its not that part, even if there is minor variations. Some parts might be slightly better at dealing with some kind of illegal conditions that are occurring but getting rid of the issue by trying to find the right part is kinda like hiding the problem.But I suspect its completely some kind of mechanical issue with shitty ribbon cable, and the parts are all fine.The highly complex PCB design of modern electronics makes the PCB and interconnects like way more likely to cause intermittent / strange problems then the parts are.banging on it reveals a problem 5% of the time.I had some rage inducing randomish problem caused by a cracked board 2 board header pin on a fluke meter last year. Fucking SMT mechanical shit And ribbon cables are something else, keep in mind that wire is like cold welded to bronze or steel forks like a wire wrap terminal. Its strange. To me, trusting it to multi-strand wire is even stranger. Its a point contact that makes a true weld on a tiny surface area, instead of a large deformation and still a somewhat mechanical bond over a large surface area with a normal crimp. Its mostly done for cost reasons. I find they like to randomly f off. If you try to jam it back in there with a screw driver your very likely not re-making a cold weld, I suspect that fork might have only 1 shot at making the weld too. Vibrations from a loud movie theater subwoofer system might have damaged the IDC connector BTW. And lord knows what IDC does with sub standard copper alloys and shit

author: tony359
author_rank: Frequent Contributor
timestamp: October 12, 2025, 08:58:34 am
content: oh I am not sure of anything right now 🙂Yesterday I powered the thing back on and it was still behaving. I wiggled the ribbons, the connectors and everything works fine. The area where I work is just a pin of the ribbon cable where the configuration data stream comes in. That was 100% working as I could see that with my scope. I need to try and bypass the switch and see what happens.Previously I had unaffected channels out of 10 so I never really considered an external issue. Warming up the e-pot was 100% raising the noise so that was another clue.Yes, there could be a cracked or faulty component for sure. I inspected the board for quite some time under the microscope. I compared all the channels with a multimeter. So far I haven't been able to find anything.I'd like to know why it's working though! 😀 Particularly because I have another board doing the same!

author: coppercone2
author_rank: Super Contributor
timestamp: October 12, 2025, 09:10:18 pm
content: wiggling is not a sure fire way to find a problem. It is often very helpful but it can be a down right menace to trace some mechanical issues down. I feel like sometimes you can 'seat' a problem where it hides for a month or two. I feel like there is a whole bunch of procedures that sometimes turn something up but its often extremely illusive lolA slow stereoscopic microscope inspection (with your eyes) sometimes might reveal a sign of damageanother rarely works one is to put it upside down and see if it still works. sometimes can help.If you happened to do solder work, and it changed something, it might mean the issue is physically nearby. Try 100% all angles high zoom microscope inspection (as much as you can stomach) of everything within like a 1 inch radius of where you had the iron. and ribbon cables and stuff.... inspect the pins for cracks and determinations. If there is connectors, look into the socket with a microscope and strong lights (or magnifier loupe). For pins, a test you can do is get fine tweezers and gently wiggle each of the pins under magnification to see if the thing its seated in might be deformed or cracked. Getting a alcohol wet ultra fine bristle brush (for makeup) to stick into female ribbon cable connectors might turn up some obstruction (and power flush them with plastic safe contact cleaner)Another test is to get pogo pin probes and test ohms on all the ceramic caps. sometimes the cracked caps might show something like kohm resistance levels when you 'press' them slightly. this is perilous because its easy to crack a cap, especially without pogo pin probes... and if not gold plated, i recommend going over your resistance probes with some polishing compound on a buffing wheel and cleaning well. Being a little 'tough' with SMT tweezers might also reveal this problemThat board has SMT parts right up near the external connectors that might get some serious force on them, this can possibly lead to some kind of fracture. Some people put some serious work into incorrect connector alignment, and those screws on the side get loose that relief the pressureAlso its possible for those caps to leak and contaminate the PCB with something partially conductrive that leads to crosstalk. Usually if you hit the caps with a soldering iron there will be a bad smell, but taking them off and looking is one of those late state last ditch options.Modern electronics have the benefit of flex lead SMT caps (some kind of conductive rubber is in there, so the capacitor ceramic is mechancially decoupled), which are much more robust. Older/cheaper SMT cap boards have rather fragile caps.Also for cheap equipment I have seen rather poor chassis mounting for PCB, like motherboard. They have all sorts of press in dohickys that are supposed to seat a screw but its like unreliable, so the screw loosen up, and the board loses stiffness from the chassis. Like 1/2 thread spring steel clips, plastic with failed glue, etc. Then it can shake in there and break itself

author: tony359
author_rank: Frequent Contributor
timestamp: October 13, 2025, 08:49:54 am
content: ThanksI will inspect again, more carefully and test more.It shall be noted that I soldered at the back of the board where there are no components. The solder was quick - the solder on the trace was done with a small C210 tip, the joint on the pin with a larger tip. I struggle to believe that there is something nearby that was affected. But it must be something somewhere.I might want to try repeating my tests with hot air and cold spray but this time focussing on components NOT on the audio channels.Thanks for taking the time to share all those tips!

author: coppercone2
author_rank: Super Contributor
timestamp: October 13, 2025, 05:16:04 pm
content: From experience, I have seen broken connections that are sensitive enough to be activated by like a feather to connections that only function when you think your going to snap the board from the high pressure appliedImagine there is some little copper in there that internally delaminated and snapped off and its almost 'rattling' around in the pcb lol