Sony trannie won't tune in

[stevehertz]

A 1965 palm size Sony trannie model 2R-21 makes the obligatory crackle when switched on (battery and connections checked) but won't (or doesn't appear to) tune in to stations. Perhaps most telling though, if you hold it close to your ear you can hear a quiet, static 'off air' rustling sound, but increasing the volume control has no effect on the level of this rustling sound. That suggests to me a problem on the AF side because surely, even if the set isn't tuning in to stations, then as with any amplifier, increasing the volume control should increase the volume of any inherent noise?

[poppydog]

This looks like yours, and the sheet is on there as well.

https://www.radiomuseum.org/r/sony_2_r_212r2.html


Regards Poppydog

[stevehertz]

Thanks Poppydog.

[Techman]

No, definitely an RF/IF/detector fault I would say.

Edit to say: The sound you're hearing is actually the general component noise from the AF amplifier, so unless the fault is immediately after the volume control at the very beginning of the AF amplifier, then the fault is likely to be before the volume control in the preceding stage or stages. Signal injection will soon confirm.

[vinrads]

The first thing that I would do is to replace all the electrolytic capacitors , don't bother checking them just replace them , Mick.

[Peter.N.]

Sounds like the local oscillator isn't running.

Peter

[stevehertz]

Thanks guys, all input appreciated. The only problem with working on this set is that it's like performing open heart surgery on a cockroach.

[dave_n_t]

Remember that you can check that the local oscillator (LO) is running by bringing the set close to another (known working!) one switched on and set somewhere in the middle of the MW band. With your Sony switched on also to MW, slowly rotate its tuning control. If the LO is working, you should hear a number of heterodynes (whistles) on the good set.


hth


dave

[stevehertz]

Here's the schematic. Meanwhile I'll do that local oscillator test.

[stevehertz]

Originally Posted by dave_n_t

Remember that you can check that the local oscillator (LO) is running by bringing the set close to another (known working!) one switched on and set somewhere in the middle of the MW band. With your Sony switched on also to MW, slowly rotate its tuning control. If the LO is working, you should hear a number of heterodynes (whistles) on the good set.


hth


dave

Just done that and yes in a couple of places I can tune in to that sucking and whistling sound.

[poppydog]

There are voltages/current stated on the emitter resistors of that sheet, I have never seen voltages stated on the schematic of a small pocket radio before. If it was mine I would check that the voltages tally with what's on the sheet first, measuring the total current drawn can also help work out what's going on.

Regards Poppydog

[ColinB]

Touch the wiper of the volume control with a finger; if you get a buzzing noise in the speaker (with the volume turned up) this will more-or-less prove the audio amplifier and speaker are OK.

[Herald1360]

A separate local oscillator is an interesting choice for a set which is challenged for space anyway.

Two IF stages and an audio preamp stage should make it quite a sensitive little set.

[GeoffK]

Are all the IF cores in place. Has it been messed around with. Check aerial and osc trimmers haven't been moved.

[michamoo]

Often just leaving them switched on for a few hours with a decent battery installed brings them back to life. May have been lurking dormant at the back of a drawer for a couple of decades. Capacitors may just need awhile to wake up after a long sleep.

[Techman]

That last piece of advice about just leaving them on and they'll gradually pick up on their own is about right.

Seeing this thread provoked me to look at a similar radio earlier today that had been dormant for a few years. I decided that a part run down zinc carbon PP3 would be better for waking up the radio than a good new battery, as if there were any problems, there wouldn't be any potential harm done to the radio with little available power. I found an old PP3 that was down to just over 8 volts and fitted it to the radio. It crackled a bit from the volume control, but no stations could be tuned in. I left it to frazzle for a while then fitted a good battery and the radio came to life, gradually improving over a few minutes of running, as all the capacitors recovered - no need to go round replacing all the electrolytics unless you really have to.

A 'buzz test' with a finger on the volume control terminal doesn't really work with this type of radio, so no point in trying it - a screwdriver blade on the terminals may produce a bit of a crackle though.

Failing that, as I've already advised, it's out with the signal generator and signal injection and the 'half split' rule applies, then when the appropriate 'half' of the circuit has been identified, it's 'half split' again, etc. No need to make hard work of a simple job, but I wouldn't be surprised if it just starts to work on its own if left for long enough.

[stevehertz]

Thanks for the interest and input guys, appreciated. I'll try the turn on and leave it method today and report back.

[stevehertz]

Ok, after having been left on for 9 hours, still no sign of life. Conflicting views on what area of the radio the fault may lie so far, any consensus or stronger thoughts now? I'm not being lazy, but working on this tiny set is going to be so awkward I'd rather have some kind of plan to work to. Thanks.

[HamishBoxer]

Can you start from the audio out stage and work backwards and if possible inject a signal?

[Station X]

I know you've got some sound, but could it be dirty contacts on the headphone socket?