Time to present the interior of another slightly older piece of equipment. This time it will be even more interesting, because I received two copies. I will see if anything from the inside can be useful to a hobbyist electronics technician, I will focus mainly on programmable circuits. Electronics is not at all an expensive occupation when recovering parts from electro-waste. Will we find out again this time? Let's find out!
We look at the back of the equipment and all doubts about its age are dispelled. This decoder doesn't even have an HDMI output. I don't know if it would still be able to receive anything, but looking at the prices it's possible to buy one for a dozen zlotys, and I don't even have a remote control....
The whole thing is built around one main PCB, with the switching power supply and the rest of the unit separately. The audio outputs (for the right and left channels) still have a tiny PCB, and there is also a separate display.
In the case of the display, we have a surprise, as there is neither a sliding register nor a dedicated controller such as the TM1650 or TM1637, but there is the well-known and well-loved ATTiny2313 microcontroller from Atmel at the time (now, after the acquisition, from Microchip). It appears that it is this MCU that does the multiplexing of the 7-segment display showing the channel codes.
The display has dots, but no colon - we won't make a clock easily. We also have an IR receiver, after all the remote has to work somehow. You could make it work at least with IRRemote from an Arduino or ESP.
As a curiosity, we have extra insulation on the bottom of the PCB on the high voltage side and the inverter in general, and on the low voltage side we have contacts from ground/casing
I had a look at the display. Strange, why so many wires when Attiny does multiplexing?
[img-1]
Both motherboards are quite similar:
On the underside we have only a few components, among others the decoupling capacitors from the main CPU:
Now let's further examine the rest of the PCB, starting with the power supply .
On the input we have rich filters to reduce EMI interference. Of course there is a fuse too. Then a bridge rectifier and a boost converter.
The inverter is based on the TOP245PN:
It can provide up to 30 W, depending on configuration and cooling capabilities.
This circuit already has a keying transistor integrated into it - below is a schematic of an example inverter:
Next we have more inverters - lower voltages are needed for the processor. In the background you can also see the AZ1117-ADJ, which is a linear voltage stabiliser with adjustable output.
L5970D - up to 1 A.
Example diagram:
The main processor is the STi5107KYA Omega from ST. On the PCB it appears with M28W320HS (32 Mb Flash) and K4H561638H (256 Mb SDRAM).
It's a shame that the Flash is in such an inaccessible DIY enclosure, otherwise something could be tampered with. I would have ripped the contents and analysed in Ghidra, and maybe I would have tried to upload something new.
Further separately we have the STV6414AD:
As far as I can see, this is simply an audio/video line switch, it is controlled via the I2C protocol.
Still here we have the RF tuner:
It is based on the STB6000, interestingly this chip operates in direct frequency conversion mode (without intermediate frequency - IF). It is controlled as usual via I2C:
And that's it for now - there's still some circuitry under the card reader, but the reader obscures the marking.
Summary
This time it's hard for me to write that the power supply will be useful, because the whole thing is as one module. It's equally hard to see playing with the main MCU, and there's not a lot of memory and capability there anyway.
Probably the biggest surprise, though, is this display module from Attina. After all, it's a representative of one of the most popular MCU families in DIY projects. It begs to be used. The only pity is that this display is without a colon. It is only useful for measurements. How about making one eight-digit display out of two?
That's it for now, perhaps in the next topic I will present some DIY based recovered parts. Or have you ever managed to recover interesting MCUs from electrical junk?
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