This “Cambridge SoundWorks DeskTop Theatre
5.1 DTT2500 Digital”,
“CreativeDesktop Theatre 2500” or CTT2500,
is a reasonably priced Dolby Digital decoder.
But after some 1000 working hours,
especially on warm places,
it shows a series error:
Occasional muting of all sound channels,
then more often until it doesn't work anymore.
A bit more rare muting when working as Dolby-Pro-Logic decoder
(true 5.1 sound feed), also called
Dolby Digital
or AC-3.
The mute signal is fed by the digital part of device.
There sits a microcontroller that crashes sometimes or later permanently.
But the only reason that is user-fixable is a defective power supply.
Because you cannot track bugs
in a (closed-source) microcontroller.
The controller is on the upper board:
Somewhere on this board is the error;
click on picture to see PCB's bottom side
Repair
Desolder the shielding plate first.
Near the voltage regulator is C218, 22 µF, where you can measure
3.3 V DC (which is fully OK) and 0.5 V AC (too much).
The capacitor has a too high ESR!
Typical for too small and warm-situated polarized caps.
Here is the capacitor C218
The actual capacity is quite out of concern, I replaced it with 220 µF and it works too.
— The C224 buffers the 5 V input for the voltage regulator.
That's all! (smiling)
Other Errors
Scratchy Volume Knob
Use cleaning spray for potentiometers.
Mutings on Volume Peaks
Another problem of power supply. You will experience a complete reboot with flashing LED lights.
In this case, the capacitor in the external power supply unit is defective. Replace it.
Upgrades
Possible:
Adapter Cinch to real speaker connectors (country dependent).
