DVBT decoder Synaps THD-2857, looking inside

Nearly twelve years have already passed since the introduction of digital terrestrial television in Poland ( Digital Video Broadcasting - Terrestrial ) and a newer version, DVB-T2, is already being launched. The very introduction of DVB-T was a kind of revolution, and the complete switching off of analogue transmitters forced the purchase of new TV sets or external decoders. Any day now, the new technology will come into permanent use and the majority of current devices will be discarded or replaced with newer ones supporting the new standard.

A lot of completely working equipment will simply go to waste . One of my neighbours has a habit of 'tossing' me all sorts of equipment that he wants to get rid of and I may be able to use something of it . Walking into the workshop this morning I saw the title character waiting for me;




The decoder is complete with remote control and completely operational. I don't use DVB-T (I don't even have an aerial) and anyway a change in broadcast standard will make reception impossible. The case is not a typical plastic box and is, apart from the front panel, made of steel, the first thing that came to mind was the use of the case. It even fits perfectly into this frequency killer .





So let's take a look at what can be used in addition to the housing . The interior, as you can see from the photograph below, is relatively poor, which was to be expected given the manufacturers' use of highly specialised integrated circuits .



So let's take a look at the main PCB;



At the heart of the decoder is the ALi M3801 ALCA, it is a so-called STB or Set Top Box. This is what manufacturers call complete decoders as well as specialised processors for video and audio processing. On the web I was only able to find information about the M3601S, but here there are probably no major differences;



Right next to it is the RAM K4B1G1646G-BCK0 from Samsung, this is a 1Gb DDR3-based SDRAM in a 64M x 16bit organisation. Right next to the power/SCART connector is the SGM8903, this is a dedicated line buffer for stereo analogue audio;



This acts as a match for the differential signals from the output of the ALi M3801 DAC to a typical line audio input (SCART), below is a typical circuit application;



Near the front panel connector you will find a UH12A which is the 1.2V equivalent of the LM1117 in a SOT223 housing. On the board there are also two pulse stabilisers in SOT23-6 (KG2UB) and SOT23-5 (AB3BA) housings, which I could not identify clearly. I didn't check the RF part located under the screen, because it would require minor devastation of the PCB and it may still be useful. On the other side, apart from a few transistors and RC elements, there is a 25Q32FVSIG memory from Winbond.







This flash memory and SPI interface contains the decoder's firmware. Another component is the power supply unit which also contains the SCART connector;




The role of the power supply controller is performed by the OB2536 chip from On Bright, this is a specially designed driver for low-power power supplies or chargers;





The power supply provides 5VDC and about 1.5~2A max, the SB360 diode (3A/60V) acts as a rectifier. According to the description on the decoder case, the power consumption from the mains is 12W max. The power supply board has been made quite decently with a sufficiently large insulation gap;




The visible narrowing of the path is probably meant to act as a fuse There is still the front panel left, this one has been simplified to the limit;








Responsible for display control is the FD650S which is a clone of the TM1650S, it provides four seven-segment displays and a 28-button keypad, communicating via an I²C interface;





The infrared receiver is a TSOP1338 manufactured by Vishay, admittedly not recommended for new devices but.... The receiver operates at 38kHz (IR carrier);





The LED display is also interesting, the character and segment shapes are reminiscent of those used in communist times . We have a +5V power supply ready to go, and with the main board removed, there is room left to put in a couple of 18650 Li-Ion cells. Perhaps a battery-network version could be made?




I need to look for material for the front panel acting immediately as a bezel for the very bright meter display. Let's not throw away immediately used equipment, let's first check what we can use .