Retrofit of SST to EU Sony ST-S770ES?

[Jckrarup]

Hello all,

This is my first post to the forum.

I have a Sony ST-S770ES tuner and noticed that a part of the PCB labeled Advanced SST was unpopulated. It seems like the Japanese version is fitted with this option, but that it did not make it abroad. The ST-S333ESB has the “Super Stable Tuner” (SST) option:

SONY ST-S333ESG

hirokun.jp

Basically, the microcontroller can modify the RF front and it should give some advantages. The MCU pins 19-22 (4 bits output) of the 770ES controls a 14066 switching controller that switches a combination of 15, 30, 62 150k resistors and thereby controls a parameter of the front end between 16 levels.

Its only a handful of components and i think it could be a fun project, just because you can…

First question is if the MCU runs the same firmware ? It wont matter populating the components of the SST section and the missing relay if there is no output.

I attach a picture of my unpopulated PCB section , annotated with component values taken from the 333ESG.

Did anyone hear of such a retrofit?

Does anyone know of a good description of what the circuit does ?

Thanks for taking the time to read my thoughts on this.

Janus

 

[AnalogSteph]

First question is if the MCU runs the same firmware ? It wont matter populating the components of the SST section and the missing relay if there is no output.

That right there is the question of the day. Have you tried probing the MCU outputs in question (or perhaps the 4066 inputs instead) to see whether they're doing anything?

I would very much be assuming that a Japan domestic market unit is not running the same firmware, after all it has to cover a completely different frequency range (76 to 90 MHz).

Does anyone know of a good description of what the circuit does ?

The page you linked to has one, for starters. Google Translate says this:

SST (Super Sound Tracing) circuit

• The instruction manual simply states that it "corrects tracking errors," but we will explain this here.
• Normally, the VT voltage of the varicap tuning circuit is controlled by the same voltage for both RF and OSC.
  • In principle, with the PLL synthesizer method, the OSC is perfectly synchronized with the broadcasting station.
  • RF may have some tracking errors, meaning that the RF may not be perfectly aligned with the broadcast station.
• The SST circuit improves as follows:
  • It is driven by two VT voltages: [VT voltage for RF] and [VT voltage for OSC].
  • In principle, with the PLL synthesizer method, the OSC is perfectly synchronized with the broadcasting station.
  • Correct the [VT voltage for OSC] to create a [VT voltage for RF] that is perfectly synchronized with the broadcast station, and then perform RF tuning.
    • Specifically, a correction is made by adding an offset voltage that brings the broadcast station reception level to its peak.
  • This minimizes RF distortion that occurs in the front end.

Sounds sensible enough.

 

[Jckrarup]

Hi and thank you for chipping in!

I tried tuning to a couple of different stations and was happy to see that the MCU output pins are active and does change! I list frequency and signal strength judged by number of bars. The pins all have pullup resistors to 12v but I can see that the MCU does pull them down! So, my conclusion is that the MCU is alive.

F. SS. OUT
93.9 75% HLLH

95.5 10% HLHH

96.5 75% HHLH

100.0 45% HHLL

On another note, even though there is not MPX filter bypass relay, the MCU does have the feature to look for the keypress, light up the Display and drive the relay. That suggests universal firmware…. At least for MPX and SST options.

I dont have the bloody 6.2v zener so I need to wait for it to arrive.

 

[AnalogSteph]

Sounds promising then.

I dont have the bloody 6.2v zener so I need to wait for it to arrive.

I am in the lucky position of being able to buy stuff like that locally. Just don't expect any premium parts.

 

[Jckrarup]

He he, ordered a box of premium Chinesium zeners…. Should arrive in 10-12 days - I will update when I have populated the board. I should have the remaining resistors and the 14066 in a drawer somewhere… so, status permpicture.

I need to figure out how precisely the output form the opamp (pin 1) is routed to the front end. I think I need to move a jumper.

:-D