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Denon DHT T100 DESIGNED TO FAIL : bad caps (ceramic caps this time)

A friend gave me a Denon DHT-T100 to look at.
Do not spend much time on it.. ok.


It had a problem, it started clicking and ticking after power on, and after some time.
(a so called intermittent problem)

Sometimes it did not tick or click, but it was basically not usable.
The clicking had a sharp click in one channel and repeated after about a second, then sound recovered and it would click and drop out again.

He told me, do not spend any time on it, yeah, right. ;-) like I would give up after 15 minutes.
I wanted to know what was going on with this thing, I found some schematic online and started measuring the usual things.

The power supply, 24V did it drop down when a tick occurred ? Difficult to find out because sometimes the thing would play for hours without a glitch.

I eventually found out the 24 V PSU, the step down SMPS on board and the LDO's were all ok, all power rails remained within spec, but it still glitched sometimes. (while power was ok)

I investigated methodically, did it occur just with the blue tooth or also with the cable? Both ..
Was it digital or analog? Was the DSP restarting? All these things were ruled out eventually.

I finally found the a signal changing during the glitch.. it was the FAULTZ signal on both the power amplifiers (class D, TPA3118)

The signal is bi-directional, you can pull it low to disable the power amplifier, and it gets pulled down by the amplifier when a short, over-temp, over-voltage, under-voltage etc occurs. It is also connected to a reset circuit.



http://www.ti.com/lit/ds/symlink/tpa3118d2.pdf

The 3 pin reset IC was finally ruled out as the culprit. (U28 was not bad)

To make a long story shorter, one power amp was detecting a failure and taking the other one down too.

I ordered a new TPA3118 and spent some hours soldering it, it has a heat-sink on the bottom and access to the pins is hindered by big caps, it was a struggle, but it got done.
The de-soldering of the thermal pad on the underside  was not easy, but with a 40 Watt big iron it finally worked.

I powered up the thing again and expected success, but was greeted by the same clicks as before.

I really had a WTF moment, you can be sure. ;-(

I had to change my plan, I knew the problem was probably thermally triggered so I took my soldering-heat-gun and turned it all the way down to 100 deg C. A very small nozzle on it, to point at potential problem components.

I pointed at specific points on the PCB to find the location of the fault and after some trial and error found 2 small capacitors that resulted in ticking/glitching very quickly.

These were the DC blocking capacitors between the TL074 analog filter and the input of the TPA3118.

I measured the capacitance, 10 uF all fine, the voltage over the caps (DC was about 9.2 Volt) and looked this all up in the schematic.
It seemed to make some sense, if the capacitors would briefly short and recover the power amp would trip into FAULTZ and recover.

Looking at the schematic I noticed the caps are specified as 6.3 Volt caps, but there is a 9.2 Volt DC on them, no wonder these things go bad! If interested, please google 'failure modes of MLCC capacitors' to learn more than you ever wanted to know about the problems with these caps.
The datasheet says the DC level at the inputs is biased to 3 Volt from ground.
I checked the schematic, the 'virtual ground' of the TL074 chips is at about 12 Volt, so 12 -3 is about 9 volt DC over the blocking caps.













My conclusion : bad specification, the blocking caps should be 25 volt or higher.
This is a design FAIL FAIL FAIL.
During startup the spikes on these caps will be about the full 24 Volt of the power supply. 

If the capacitors are really just 6.3 Volt as the schematic suggests, then all these DHT T100 sound bars will break down very quickly.

What you need to do is replace caps C126, C138, C154, C160, C171, C184, C199, C210 with higher voltage ones.

Also, the caps are 10 uF and the reference design by TI specifies 1 uF, the 10 uF brings the high pass filter's corner frequency down to 1.6 Hz, which is just plain nonsense. Better use a 1 uF cap of 50 Volt than a 10 uF cap of 6.3 Volt. It sounds just the same but does not break down within 2 years.

I replaced the caps with some 25 volt ones of 4.7 uF I had in stock.
Powered up. Problem is gone now.
I can heat it up, cool it down whatever, it is really gone.

So if you ever have no-sound or clicks/ticks/glitches take a look at the DC blocking caps.

I spent a lot of time to find this problem, but I get a good feeling that I cracked this one!
Hope this helps you in repairing your system.
If you have no experience with electronics then this is not something you can fix, please ask someone with soldering experience. I also take no responsibility for things you do or accidents you make.

(This is the broadest possible legal disclaimer you can think of)

Good luck and happy tinkering.
Edwin (Oetel-x)

Reacties

Unknown zei…
I have a similar problem with mine - from time to time a popping noise can be heard from on of the speakers, which most of the time is followed by all noise being lost for a short space of time. But then it can work fine for some time after. Very frustrating! It is outside of its warranty, and Denon and Richer Sounds will not help me. Is it a financial write off?...
#oetelx zei…
If you can find someone who can replace the capacitors (the ones with red circles) you might have some luck. It is not the cost of the capacitors, it is just the amount of work and time that costs money.
Harvey zei…
I have a dht-t110 doing exactly this...would I be better putting in 50v 10uf caps or 50v 1uf caps instead please?
#oetelx zei…
I doubt you can find a capacitor of 50V 10uF that fits in 0805 space.
Just use any MLCC cap 16V or higher, 1uF or bigger. You will be OK.
Unknown zei…
Are the capacitor numbers and locations the same on the DHT-T110?
#oetelx zei…
I would like to help, but I just do not know. Maybe you can get the schematics somewhere, I do not have this information.
Unknown zei…
Thanks Edwin, do you know a good place to order the schematics?
Erwin zei…
Thanks a lot for your blog! Using your guide I was able to repair a Denon DHT T110 sound bar. It has the exact same PCB as shown in your pictures. My first successful SMD soldering repair job!
Unknown zei…
I’ve stripped down my DHT-T110 and can now confirm the faulty capacitors are in the same position as your photos of the T100
Thanks again
Unknown zei…
Hello, i have problem with my dht 100, it couldn't wake up from sleep. When I cut the power and turn on again for few seconds everythings work properly, all buttons work, but when the backlights turn off then the denon doesnt react on the buttons the sounds is ok (still Play)
Unknown zei…
Hello, I have promblem with my dht100, when I plug it to power everything work good, but after few seconds when the buttons backlights turn off the denon doen't react on buttons the sound still play. To resten I must cut the power and again denond work properly by few second, it looks that denon could't weak up from sleep mode? what could be the reason. Thanks for help
Unknown zei…
Hello, I have promblem with my dht100, when I plug it to power everything work good, but after few seconds when the buttons backlights turn off the denon doen't react on buttons the sound still play. To resten I must cut the power and again denond work properly by few second, it looks that denon could't weak up from sleep mode? what could be the reason. Thanks for help
Stevie zei…
Right I'm proper fed up off this rubbish I have now bought two denonDHT-110 and both have had the same fault the problem is it works fine then after about 15 minutes it cuts out and sound returned what the hell is going on
Unknown zei…
Hi Edwin. Brilliant piece of tech work. I am about to order some capacitors. Is the size of them 0805?? If not could you give me the size please as there are a few different sizes I understand. Thanks in advance of your kind help. Jeff.
Unknown zei…
I had this problem I managed to solder these capacitors in myself with it being my first ever attempt at soldering smd components.
To my surprise it now works fine so I am really pleased.
I would never have found the fault without this blog so i am really grateful for the help and the info.
Unknown zei…
I also have this problem with my T100 a couple of weeks now.
Looking at the pictures of the circuit boards, this capacitors are very, very small.
My experience is from the years 60-70 with big capacitors.
How to disassemble this capacitors?
By the way, your name looks very Dutch.
Greetings, Rob Willemsen (70+)
#oetelx zei…
Hello Rob,

Yes I am Dutch, living close to Eindhoven. The capacitors are 0805 size MLCC. These things are best handled with ceramic tweezers and a heat gun. If you are bold, you might use a normal soldering iron with a wide blade, but it takes practice. Good luck.
Unknown zei…
First of all, my apology for writing now in Dutch, but I don't know to write this in English.

Mijn elco's zijn nog "ouderwets" groot blauw.
Het type, welke ik op de foto's zie, nog nooit mee gewerkt.
IK zal in Amsterdam bij enige elektronica zaken eens te rade gaan. (Ik stam nog uit het buizen tijdperk).
Unknown zei…
Same device, same problem, after a while the cracklings got worse some of them very loud. So i bought the caps and soldered according to your plan. Worked for me!
Thank you so much, your work is appreciated.
Unknown zei…
Edwin - excellent fix. I can't imagine it will happen but if we ever cross paths I'll buy you a beer.
Thanks, Graeme
Clive zei…
My DHT 100 has just started popping tuning on and off too.

Don't you just love the Web, guidance on such an esoteric problem so expertly detailed.

We have a hot air resoldering tool at work and if we don't stock a suitable cap I will be amazed.

Thanks to you Edwin, nerds on the world unite. Clive
Darcy zei…
Hiya how much do the capacitors cost to replace. I have exactly the same problem. Tried to contact Denon no answer. (useless)
Fen411 zei…
Hi there has anyone done a Disassembly walkthrough?
Phil123 zei…
Hello Edwin, I have the same popping coming through the right side only, and am going to attempt your fix myself, as I'm reasonably technically inclined, I found 50v 1uf ceramic capacitors, I'm assuming they will be okay, although a slightly different shape? Thanks. Philil
K1mbo zei…
Hi, I've just had a local technician repair my Denon who fitted 16 volt caps. Unfortunately, after a few hours use the fault returned. Any suggestions?
K1mbo zei…
Hi, I've just had a local technician repair my Denon who fitted 16 volt caps. Unfortunately, after a few hours use the fault returned. Any suggestions?
#oetelx zei…
The full 24 Volts will be on the capacitors during startup of the device. You need 25 Volt rated or higher capacitors to be sure that they will not be damaged.
Unknown zei…
Nice repair manual! Seems replacing those 8 bad caps did the trick for us too!
Symptoms were clicking after some time and then also hissing and sound loss for like 1/2 a second, then on again, repeat.
Replaced with 1µF 0805 50V - although the ones Denon used are quite slim, so it is a bit tricky to fit regular ones.
Use your ohm meter to check after soldering: one side has zero contact between the two caps (C171 and C184 for example), the other should have about 80 ohms.
I hot air soldered with a lot of flux paste and the original solder needed up to 350°C to get lose.
Nige Ips zei…
Fantastic work! I thought my DHT 100 was destined for scrap as there was little chance I could have diagnosed the click problem and unlikely to find anyghing on the 'net. Boy I was wrong! Didn't have replacement SMD capacitors but was able to solder some junk box 1uF 25v tantalums onto the pads. Now working fine! Thanks!
EskildP zei…
Thanks for publishing this! I managed to fix my DHT-T110. My 0805 capacitors were a bit bigger than the original ones, but still possible to solder to the pads.
Mark Lawton zei…
I bought a cheap one off eBay.

Took it apart and found those capacitors to be ok.

On the one channel if you put your finger on it before the TL074 you get deep mains hum from the speaker. The other channel it sounds tinny doing the same but you get the same hum after the TL074 if you put your finger on it.

So I'm wondering if it's worth swapping the op amps out and trying that.

PSU is 23.83V DC and those little caps seem to esr ok.

On the curve tracer the caps you suspect all look ok. All read the same.

So other than cap changing it all and the two op amps I'm a bit stuck!

I'm going to do the op amps 1st then re test the and caps at work on the tracker.

No sound at all btw but all the rest seems to work. I reckon the power amp chips are OK.

Any ideas? Thanks 👍
#oetelx zei…
I would suggest changing the caps anyway. The original ones are not up for the job. The DC voltage across the caps during startup is 24 volts.
After some time they seem to recover. (or fail intermittently)
Also when this has been done, use a signal tracker, insert some sine wave at input and follow it to the power amplifier.
This will prevent un-needed work,
I made the mistake of changing the power-amps before understanding the real problem.
Waste of time, parts and energy.
Try to analyze the situation before exchanging difficult parts.
Good luck with your adventure.
Mark Lawton zei…
Hi again,

Looks like I was unlucky. I replaced all of those caps. I used 10uf multilayer ceramic 35V working. I did previously try 1uf 16v working and no sound.

Powers up and pairs with phone but no sound. Phono in 3.5mm no sound either.

Replaced all the electrolytic caps as well. Some were a bit out but not bad.

I'm wondering now if it's the little al to D chip on the input, or the big preamp chip gone.

Can see the small A to D chip on eBay so may risk that in case it's killing the inputs.

I'd appreciate any input now too please!

I'll be looking for another one then could sell this off for spares on eBay.

Hope everyone is good and someone somewhere fixed one!
Mark Lawton zei…
I'm thinking of changing the CS5346-CQZ, as no inputs are working at all. No sound at all. They aren't too expensive.

Being a multilayer board the only place I can inject a signal and it works is just before the power amp chips on the two op amps

The power supplies all seem to be there, so this leaves the CS5346-CQZ, and the other large preamp chip.

The other chip seems to be harder to get hold of though and is obsolete.

All ceramic and E-caps capacitors were changed.

Wonder if anyone on here has had a more involved fault?

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