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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)

Comments

Unknown said…
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?...
OETEL-X said…
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 said…
I have a dht-t110 doing exactly this...would I be better putting in 50v 10uf caps or 50v 1uf caps instead please?
OETEL-X said…
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 said…
Are the capacitor numbers and locations the same on the DHT-T110?
OETEL-X said…
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 said…
Thanks Edwin, do you know a good place to order the schematics?
Erwin said…
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 said…
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 said…
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 said…
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 said…
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 said…
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 said…
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 said…
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 said…
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+)
OETEL-X said…
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 said…
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 said…
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 said…
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 said…
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 said…
Hiya how much do the capacitors cost to replace. I have exactly the same problem. Tried to contact Denon no answer. (useless)
Fen411 said…
Hi there has anyone done a Disassembly walkthrough?
Phil123 said…
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 said…
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 said…
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?
OETEL-X said…
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 said…
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 said…
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 said…
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.

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