Sony ST-S770ES tuner memory issue

[miggyboys]

Hi all

I've got a Sony ST-S770ES tuner which is virtually fully working however, the memory/preset function doesn't remember stations. Does anyone know which component may need replacing which is responsible for it? There's no battery on the circuitboard (or not one I can see). I've enclosed the service manual for you electronic engineers out there!

Thanks in advance!

 

[AnalogSteph]

The component to look for is a supercapacitor a.k.a. Gold-Cap(R) (a Panasonic trademark), to be recognized by their 5.5 V rating and capacitance rarely any smaller than 0.047 F (yes, Farads). Should be close to the main microprocessor. Tuner manufacturers at times find superb hiding spaces for them, including buried underneath the VFD where it's nice and toasty.

EDIT: There it is, C605:

Sits right in the corner of the main tuner PCB:

 

[miggyboys]

The component to look for is a supercapacitor a.k.a. Gold-Cap(R) (a Panasonic trademark), to be recognized by their 5.5 V rating and capacitance rarely any smaller than 0.047 F (yes, Farads). Should be close to the main microprocessor. Tuner manufacturers at times find superb hiding spaces for them, including buried underneath the VFD where it's nice and toasty.

EDIT: There it is, C605:
View attachment 311806
Sits right in the corner of the main tuner PCB:
View attachment 311809

Hi AnalogSteph

Thanks so much for looking at this! I really appreciate your input. I can see it clearly now.

Best regards

 

[miggyboys]

Hi AnalogSteph

I saw this on another forum, in relation to this very tuner and same supercapacitor. Would you agree with this or not? If so, would you know which this is?

Also replace the diode in the supply line feeding the cap. The diode is for preventing the cap becoming empty into the supply when power is off. Usually the diode gets leaky by the large in rush current when power is applied. Replace by an 1N4004 type regardless what Japanese type is used.

Regards

Miggyboys

 

[AnalogSteph]

That would be D606. (And any 1N400x should do.) I imagine a major factor in that would be C604, a tantalum capacitor (10µ/6.3V). IMHO that guy is underspec'd (never pick a tantalum's voltage rating that tight!) and may also be suffering from increased leakage as a result of inrush current, which would suck your C605 dry as well. Ironically it was originally picked for low leakage current. If C604 is still fine, add a small resistor in series with D606 when you change that, like 22 ohms.

Supercaps can also start to physically leak, so watch out for that as well. And check fusible R626 for tolerance, these things have a habit of failing open.

TP602 can be used to check current consumption in standby, employing a multimeter to measure the voltage drop and using Ohm's Law. From the µPD75108 datasheet, current in stop mode should generally be <10 µA, i.e. < 10 mV over TP602.

 

[miggyboys]

Hi AnalogSteph

That's some reply! I really appreciate your technical advise and expertise, many thanks.

Best regards

Miggyboys

 

[Prana Ferox]

Failures of these supercaps are a very, very common problem in old digital tuners. Luckily the symptoms are usually limited to this, not remembering presets. The issue is mitigated somewhat by having very few listenable FM radio stations left to remember.

 

[miggyboys]

I'm in Leeds, England. Luckily in the UK, there are quite a few FM radio stations left. The quality of them is still decent. DAB sounds awful here, DAB+ a very small number.

 

[AnalogSteph]

DAB sounds awful here, DAB+ a very small number.

Still? If memory serves you guys have some pitiful DAB data rates, not a good match with the layer 2 audio that the original DAB standard uses.

https://en.wikipedia.org/wiki/Digital_radio_in_the_United_Kingdom says:

In 2020, most commercial stations use only 32–64 kbps (DAB+ with HE-AAC codec) while those stations maintaining the old DAB standard (MP2) have switched to mono with 64–80 kbps.[1]

Oof.

 

[miggyboys]

Correct, the DAB data rates are truly awful. At lower volumes, it's often difficult to clearly hear people's voices, especially if they don't speak clear English. I listen to Talksport and BBC Radio 5 live for football chat / match commentary as millions of people in the UK. They both broadcast at 64kbps! Even BBC Radio 1 on DAB is only at 128kbps. Bear in mind that I have external roof mounted FM & DAB aerials that enable excellent reception. On FM, I can listen to stations that are 60 miles away.

FM is always my first choice for radio. BBC Radio 4 is crystal clear with lots of depth, dynamic range and width. DAB is used as a second option but it's hard work, tiring on the ears. The authorities should have enforced a minimum bit rate as standard. Internet radio is also problematic given a load of radios in the UK have stopped working because the provider has shut down a server, therefore making the whole radio redundant. Plus internet radios are very expensive compared to FM radios though many people listen to internet radio via other devices like phones, streamers, PCs etc.

But radio listening is still very popular in the UK. 50m people listened to the radio in Q2 2023.

 

[sktn77a]

For what it's worth, I have the ST-S550ES - a contemporary of the ST-S770ES and the memory presets never worked from new. I even exchanged for another during the first week because of this but the replacement didn't work either. I assumed it was a defect in the design.

 

[miggyboys]

Thanks for sharing your experience. Hopefully once I've replaced the supercapacitor as a minimum, it will be resolved. I'll post back on here once I've done it.

 

[LTig]

For what it's worth, I have the ST-S550ES - a contemporary of the ST-S770ES and the memory presets never worked from new. I even exchanged for another during the first week because of this but the replacement didn't work either. I assumed it was a defect in the design.

I have the ST-S555ES which I bought new in 1987. It still keeps its memory presets to this day without any problems, so I think the design has been improved. The only thing which failed was the relay which switches between the 2 antenna inputs. I just soldered in a short cut since I never needed two inputs at the same time.

 

[AnalogSteph]

I have the ST-S555ES which I bought new in 1987. It still keeps its memory presets to this day without any problems, so I think the design has been improved.

In which case it would have been misimproved, as the model in question in several years newer (1991-92).

For what it's worth, I have the ST-S550ES - a contemporary of the ST-S770ES and the memory presets never worked from new. I even exchanged for another during the first week because of this but the replacement didn't work either. I assumed it was a defect in the design.

Pretty much has to be. Either that, or they had a bad batch of supercaps or something. Might be fun to troubleshoot with a DMM / scope.

Hmm, that guy looks quite similar to my old Onkyo T-4650 (aka T-4500). Maybe it has a similar problem of the /HOLD signal not going down fast enough so the µP sucks the supercap dry before finally going to sleep. I'll had to study the datasheet for the LA5667 regulator... Hmm, that guy is clever, it has a reset signal output that goes low when the input voltage drops below a certain threshold. So in theory the µP should be told to go to sleep the instant the input voltage to the regulator goes away. Either this is not happening, or there is something else going on.