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Old 12th Jun 2019, 8:36 pm   #21
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

oh, well, it seems the signal I was tracing through the IF and onwards was in fact just the IF oscillator! Turning the modulation on and off made not the slightest difference to the signal on the IF! So whats coming out, distorted, from the AM subsystem IC is just a badly distorted IF oscillator signal!
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Old 13th Jun 2019, 6:18 am   #22
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Default Re: No LW/MW receive - Sony ST-S311

The 5v everywhere thing could just be where the internal bias system sets things for analogue inputs and outputs.

-35dBm would be 4mV PD in 50 Ohms. With AM inputs being high Z, it's likely got 8mV at the input. Specs for the chip are in dBuV so call that +78dBuV

The datasheet quotes power consumption with 107dBuV and with no signal. so 78dBuV is within the ballpark.

Ah, at 80dBuv it quotes <1% THD and "detection output" between -15.5 and -9.5 dBm... whatever detection output may mean.

It should be working properly at that RF level, though the numbers above are for 30% mod.

As a reality check, as a kid in Almondbury, my crystal set gave audio out the headphones which could be heard several feet away from the phones, if tuned to Pole Moor at the other side of huddersfield. So the RF level must have been in the 100mV region and normal radio sets in the area handle it.

S-meter output... 0 to 0.5v quiescent about 4.5v with 107dBuV RF... pin16 That ought to be checkable to see if the thing is running and AGC is alive.

Datasheet application circuit number 1 gives quiescent DC volts for all pins.

I wonder if a zap has discombobulated only the RF amp stage and just left the chip very deaf? so your -35dBm is only just lifting the rest of the receiver structure out of its floor. The S meter pin voltage as you vary the RF might throw light in this area.

David
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Old 13th Jun 2019, 6:26 am   #23
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Default Re: No LW/MW receive - Sony ST-S311

Lateral thinking:

I suppose your organisation does have a preferred supplier that would supply an entire new receiver?

Look at it as a wonderful saving achievable as a result of good tight supply chain management!

David
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Old 13th Jun 2019, 7:42 am   #24
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

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Lateral thinking:

I suppose your organisation does have a preferred supplier that would supply an entire new receiver?

Look at it as a wonderful saving achievable as a result of good tight supply chain management!

David
weeeell... you'd like to think so, with the nature of what we do... but I essentially decided to try and repair this when the person tasked with buying a new one called me to his office to look at the one he was thinking of getting, and explain to him why it didnt do LW even though it was 'AM'

I could also just send it back to our own repair people... but I want it to work!
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Old 13th Jun 2019, 8:19 am   #25
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

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Originally Posted by Radio Wrangler View Post
The 5v everywhere thing could just be where the internal bias system sets things for analogue inputs and outputs.

-35dBm would be 4mV PD in 50 Ohms. With AM inputs being high Z, it's likely got 8mV at the input. Specs for the chip are in dBuV so call that +78dBuV

The datasheet quotes power consumption with 107dBuV and with no signal. so 78dBuV is within the ballpark.

Ah, at 80dBuv it quotes <1% THD and "detection output" between -15.5 and -9.5 dBm... whatever detection output may mean.

It should be working properly at that RF level, though the numbers above are for 30% mod.

As a reality check, as a kid in Almondbury, my crystal set gave audio out the headphones which could be heard several feet away from the phones, if tuned to Pole Moor at the other side of huddersfield. So the RF level must have been in the 100mV region and normal radio sets in the area handle it.

S-meter output... 0 to 0.5v quiescent about 4.5v with 107dBuV RF... pin16 That ought to be checkable to see if the thing is running and AGC is alive.

Datasheet application circuit number 1 gives quiescent DC volts for all pins.

I wonder if a zap has discombobulated only the RF amp stage and just left the chip very deaf? so your -35dBm is only just lifting the rest of the receiver structure out of its floor. The S meter pin voltage as you vary the RF might throw light in this area.

David
Cheers David,

well the s-meter output isnt! There is no output from it!

'scoping the IF oscillator resonator I could barely get a trace at all, but it must be running as I can see the 450kHz signal cleanly on the IF filter. But thats all I can see - a nice clean 450kHz sine wave! No modulation at all, whatever I set the mod level to on the test set. Im pretty sure as well that in a working set I shouldnt be seeing that IF oscillator signal, even low and badly distorted (almost a double triangle wave!) at the output to the audio stages!
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Old 13th Jun 2019, 8:59 am   #26
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Default Re: No LW/MW receive - Sony ST-S311

The resonator on pin 15 isn't an oscillator. It's emitter decoupling for the S meter amp... I think it's to make the S meter response very narrowband so auto search tuning finds the carrier of a signal to stop on. I don't think you'd see much signal there on it as it's used to do a low Z dip at the carrier freq. This is also a long way downstream of the IF filter.

Seeing 450kHz without mod on the IF filter looks very wrong.

IF is 450kHz, so LO should be 450k above tuned freq. Can you wave aprobe in the air near pins 18 and 19 and get a sniff of it?

David (About to go QRT and drive up to Scotland)

The IC datasheet is clearer about what's going on than Sony's schematic.
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Old 13th Jun 2019, 9:38 am   #27
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

oh, so it is! well, not seen that before! Well that explains why there was barely any detectable signal on it!

Maybe im too used to working with dual conversion SSB receivers! Now I think about it there wouldnt be a 450kHz oscillator!

The LO (thanks! Ive been putting IF osc because for the life of me the term 'LO' wouldnt come to mind!) comes from the PLL, now I know that works for the FM side, but i'll check it anyway tonight.
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Old 13th Jun 2019, 11:01 am   #28
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Default Re: No LW/MW receive - Sony ST-S311

I realise that this goes against the whole "repair and restoration" spirit, but the tuner in question is worth very little and there are lots of them around- if this is a commercial repair, I would be tempted to look for a second hand one of these, or the cosmetically different but functionally very similar ST-S370 (also featuring direct keypad frequency entry, presumably useful in a broadcast monitor?) for 10-15, maybe less if you're only slightly lucky. (With confirmed working AM section, naturally!)

Hang onto the original for a "rountuit" personal repair,

Colin
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Old 13th Jun 2019, 11:09 am   #29
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

Colin,

I cant go too much into it, but lets just say that theres an aspect of 'office politics' at play... (which I might be able to turn to my advantage!)
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Old 15th Jun 2019, 9:10 pm   #30
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Default Re: No LW/MW receive - Sony ST-S311

Well, new IC arrived and was installed. Receiver worked! Clean 1kHz audio out from the detector, good waveforms on the IF, etc, display indicating signal meter bars full and 'tuned' indication.

Then a few minutes later, it died again! For a while I was getting something like the right scope waveforms on most pins, but now im back to the same horrid distorted traces as before.

Im at a loss! The supply voltages are good and within the chips spec, theres no obvious overheating, and a good going over anyway with freeze spray showed no changes.

What could slowly kill a chip other than heat?
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Old 15th Jun 2019, 11:18 pm   #31
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Default Re: No LW/MW receive - Sony ST-S311

Hmmm, think I may have found the problem! (or at least one of them!)

Careful comparison of the voltages on the IC against the quiescent values given in the data sheet showed almost everything to be within a couple dozen mV of where expected, except two pins, which were closer to a volt out. One was supposed to be 0v and was 0.9v - that was the signal meter line. The other was the IF amp input pin, which was about 1v too low. This connects to one side of the ceramic filter...

Checking the filter was none too easy - the IF filtering is a Toko module consisting of a tuned IFT and a ceramic filter, electrically separate but packaged in the same plastic housing. Had to unsolder the entire thing and remove it to test.

The leg of the filter that goes to the IF amp input pin reads 3k to ground! The other leg infinite at DC.

Bypassing the IF filtering entirely with a 10n cap, and the set now indicates tuned with a signal greater than 150uV (-65dBm), and I can trace the demodulated audio tone as far as the input of the LA3401 IC. Ive no audio output on AM though, there seems to be another issue with the AM/FM select voltage to that IC.

Im somewhat stumped now though. To go further I need to replace the ceramic filter, but the filter module seems to be unobtainable. Its a Toko part marked 4047 1311 93507. I could probably remove the IFT from it and refit that on its own, and fit a separate ceramic filter if I can find one. Ive none in my junk though, all mine are 455kHz and this is 450kHz.
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Old 15th Jun 2019, 11:43 pm   #32
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Default Re: No LW/MW receive - Sony ST-S311

Hmm, intriguing! I do recall a Murata data sheet somewhere sometime where they were quite stringent that there should be no DC whatsoever on input or output pins, I assumed maybe something to do with electrolytic degradation of the interfacing bonds? Perusal of quite a few tuner circuits suggests that this guidance doesn't always get followed, though.

For quite a long time now, I've used a basic compact old Rotel tuner (RMT-80L) as an aux hifi source, basically for R4 LW and R5 MW. It developed crackling and intermittency on the AM bands, traced to the little SFU455A between IF amps. Sure enough, this had output pin "live" to bias/AGC, making me wonder if this had caused filter failure. I took the opportunity to replace it with a CFUM450E, fitted "dead bug" style under the PCB and now isolated with 22n to IF amp base. (The shift to 450kHz to get rid of the 909kHz whistle!) Looking through many Rotel tuners of the era, the same AM topology crops up again and again without ceramic filter isolation...

I wonder if Sony have also left the filter "live" to DC- I suppose something like corrosion or a tin whisker-type syndrome could develop in time, but usually well out of warranty, for the sake of farthings' worth of isolating capacitor!

Colin
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Old 16th Jun 2019, 11:39 am   #33
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

Quote:
Originally Posted by turretslug View Post
Hmm, intriguing! I do recall a Murata data sheet somewhere sometime where they were quite stringent that there should be no DC whatsoever on input or output pins, I assumed maybe something to do with electrolytic degradation of the interfacing bonds? Perusal of quite a few tuner circuits suggests that this guidance doesn't always get followed, though.

Colin
This has become a common problem on many Yaesu radios, especially the FT-857. I had to have the filters on mine replaced and blocking capacitors installed.
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Old 16th Jun 2019, 12:13 pm   #34
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Default Re: No LW/MW receive - Sony ST-S311

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Originally Posted by Martin G7MRV View Post
... the IF amp input pin, which was about 1v too low. This connects to one side of the ceramic filter...

Checking the filter was none too easy - the IF filtering is a Toko module consisting of a tuned IFT and a ceramic filter, electrically separate but packaged in the same plastic housing. Had to unsolder the entire thing and remove it to test.

The leg of the filter that goes to the IF amp input pin reads 3k to ground! The other leg infinite at DC.

Bypassing the IF filtering entirely with a 10n cap, and the set now indicates tuned with a signal greater than 150uV (-65dBm).
I did suggest checking it. They do seem to be fragile and go open circuit on their own.

You could fit a ceramic filter of same frequency out of a 6 radio. Better than a capacitor
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Old 16th Jun 2019, 12:23 pm   #35
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

Indeed you did. The only reason at the time I didnt, other than a check that it wasnt short, is with it being part of a combined module with the IFT, a bit of a pig to remove from the board. Plus at the time I considered the slightly off voltage to be 'near enough', it was only with the new chip in, and the way it died off after a few minutes, that I realised something was amiss elsewhere.

Ive no spares, junk, old PCBs etc, with anything for 450kHz! Everything I have is 455.
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Old 16th Jun 2019, 12:48 pm   #36
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

Seems theres another fault with selecting the AM by the MPX decoder IC.

Between that and the filter, ive decided to BER this set. Since a 2nd hand working one can be had for well under 50 shipped. If I account for the time ive spent fault finding it at my working hourly rate, plus the cost of the AM chip, its just not worth any further effort.
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Old 16th Jun 2019, 12:57 pm   #37
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Default Re: No LW/MW receive - Sony ST-S311

Oh well, I can understand your conclusion there. Thanks for the heads up re. the FT-857 problem- once again this forum shows its utility in connecting similar problems encountered by different interest groups! I found this thread re. FT-857 problems that probably also has application to AM tuners of a certain age;

https://www.eham.net/ehamforum/smf/i...,119778.0.html
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Old 16th Jun 2019, 4:46 pm   #38
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Default Re: No LW/MW receive - Sony ST-S311

Well, the thread may be informative for others. If you have space, perhaps store the radio for parts or to give to someone?

Sorry to hear it's not worked out.
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Old 18th Jun 2019, 7:44 am   #39
Martin G7MRV
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Default Re: No LW/MW receive - Sony ST-S311

Ive too much junk as it is! So it will end up in the WEEE skip im afraid,

It is fixable, but just not worth it. However, if they decide to get a working 2nd hand one of the same model, I will insist on modifying it with a blocking capacitor to the ceramic filter!
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