In my case, whereas my old Sony DVR is able to receive all channels perfectly, the PlayTV breaks up and skips, mainly on ABC/ABC2. I'm no expert, but put this down to a cheap design without pre-amplification.
I had a thought; with USB connected to the unit (and therefore 5V +/- 0.25 and capability to deliver 500mA), why not devise a simple in line amplification solution drawing on no external power source? Sure I can buy a cots distribution amplifier, but yet another power pack when USB is available?
Time then to investigate the PlayTV PCB. Here's the front:
and here's the back, flipped for convenience:
I'm not an electronic engineer and know little more than basic electrical theory, but the first thing apparent to me is that the board uses contacts 2/3 only (USB data) and does not use the 5V bus power (contact 1).
That is, from the micro USB spec:
1 VBUS Red
2 D- White
3 D+ Green
4 ID <Ra_PLUG_ID
5 GND Black
Shell Shield Drain Wire
Not knowing anything about USB, I can only guess power for the USB and DVB circuitry is drawn directly from data signal itself (order of a few hundred millivots on/off depending) and assume likewise the LED is powered by some sort of rectification of this.
So far so good then - 5V seems available for use. After some further research, it seems that some STBs have the ability to inject the source coax with 5V DC to power an upstream masthead amplifier. Such an amplifier is shown here. I have ordered one and now just need to figure out how to solder onto that tiny tiny 5V rail. Any tips are welcome. Also, without a schematic, I'm not sure of the implications of placing an additional 5V DC onto the DTV signal. I presume however that with other types of masthead amplifiers being common fare, this is not doing anything unusual.
It's a multi-layer PCB. The 5v rail from the USB connector is definitely used, could be connected to an internal layer from any of the multiple via's located around the USB jack.
ReplyDeleteYou could probably get 5v from any of the larger ceramic (brown) capacitors (use a multimeter to find which side has +5v on it), for the most part they're simply supply rail filtering / bypass capacitors.
Good suggestion. Being multilayer would explain in part why I couldn't figure out how certain other bits connected together - much of it wasn't making sense.
ReplyDeleteAfter trying all the caps above and below the board, there seems to be 3.3V and 1.9V rails happening. Although 5.1V is output by the PS3 USB, I've not found this anywhere on the PCB yet. So I guess this means a voltage divider somewhere, but I can't see anything that looks like a resistor. Maybe you can?
Ok found the voltage divider - it seems to be an IC with 3.3V, 1.9V and 1.2V outputs. See next post.
ReplyDelete