Sony trannie won't tune in

[stevehertz]

PJL, no-one has been in this set before, I can clearly observe that.

I'll measure the trannie base voltage.

Thanks to all, appreciated.

Will report back.

[Goldieoldie]

How about popping in a silicon NPN transistor such as a bc549 etc and see what happens.
It won't do any harm and if the radio does Spring into life but low volume you could adjust the bias if the circuit is meant for a germanium transistor
You never know it might work ok without changing the bias !
Cheers
Pete

[stevehertz]

My investigations seem to complicate matters, not ease them. One by one..

I fitted a MPSH10 NPN Si trannie for X4 and the radio did not work.

The voltage across R12 (X4 emitter) was 6V - clearly totally wrong, schematic says 0.33v (as best as I can read it).

R12 removed from cct, it is marked 300Ω and measures 290Ω, so ok. Although schematic says 470Ω ?

Voltage across R8 (X3 emitter) measured as 0.6V which I believe is what schematic says - hard to read. R8 is marked 300Ω and as above, schematic says 470Ω.

As I'm pretty sure that X4 was faulty (cracked & corroded lead) then I'm thinking that fitting the correct replacement Ge trannie would bring the bias voltage across R12 to how it should be, in other words, fix the fault?

Footnote: I wish people who thoughtfully scanned service data would equally thoughtfully scan at a decent resolution! So often I come up against service data that is unreadable to any degree of accuracy, rendering it very frustrating if not pointless or even misleading at times. Rant over.

[ms660]

Originally Posted by stevehertz

My investigations seem to complicate matters, not ease them. One by one..

I fitted a MPSH10 NPN Si trannie for X4 and the radio did not work.

The voltage across R12 (X4 emitter) was 6V - clearly totally wrong, schematic says 0.33v (as best as I can read it).

R12 removed from cct, it is marked 300Ω and measures 290Ω, so ok. Although schematic says 470Ω ?

Voltage across R8 (X3 emitter) measured as 0.6V which I believe is what schematic says - hard to read. R8 is marked 300Ω and as above, schematic says 470Ω.

As I'm pretty sure that X4 was faulty (cracked & corroded lead) then I'm thinking that fitting the correct replacement Ge trannie would bring the bias voltage across R12 to how it should be, in other words, fix the fault?

Footnote: I wish people who thoughtfully scanned service data would equally thoughtfully scan at a decent resolution! So often I come up against service data that is unreadable to any degree of accuracy, rendering it very frustrating if not pointless or even misleading at times. Rant over.

The schematic I'm looking at is very clear to me:

https://archives.doctsf.com/document...2c86a5cd2c4804

On that schematic X3 emitter is shown as 0.16V (160mV) the 330uA emitter current is also a clue.

Lawrence.

[stevehertz]

Thanks Lawrence, that version is as clear as day. Much appreciated.

So, it would appear that the emitter voltage of X3 that I measured as 0.6v is also wrong as it should be 0.16V.

I need to do further checks.

[ms660]

Originally Posted by stevehertz

Thanks Lawrence, that version is as clear as day. Much appreciated.

So, it would appear that the emitter voltage of X3 that I measured as 0.6v is also wrong as it should be 0.16V.

I need to do further checks.

To me, using Ohms Law, 0.6 Volts does not compute.....Check resistance from emitter to ground, your meter or your method.

Lawrence.

[Dickie]

Originally Posted by stevehertz

.....I'll measure the trannie base voltage.

Thanks to all, appreciated.

Will report back.

Did you measure the base voltage?

[PJL]

The first step is to confirm if this set is the same as the circuit diagram. What markings are on the other transistors? We also need to know the values of R10 and R11 as they may differ from the circuit. R10/R11 set the bias for X4 so if they are the same as the circuit you need a germanium NPN transistor.

[stevehertz]

I have now, after being able to view nice, clear, layout and schematic diagrams (thanks to Lawrence) refitted a MPSH10 NPN Si trannie for X4 but this time oriented correctly! So the voltages I gave in post 43 are now superseded as follows.

HT at junction of R9 & R23 = 7.77v
Battery drain = 6.2mA
Voltage across R9 = 6.3V
X1 base V = 1.09V
Voltage across R2 = 0V (X1 not turning on or faulty, or R2 o/c?)
R5 = 2.88V
R6 = 6.51V
R12 = 1.59V
R11 = 2.12V
R10 = 5.44V
X3 base V = 1.26V
X4 base V = 2.12V

I have replaced with new ones: C9, and D for a small silicon signal diode.

Now, there is a quiet motorboating type sound that increases with the volume control. Still unable to tune in or hear any different sounds when tuning.

Photo below of the removed X4. I take it be a 2SC403 ? But when you look up the spec for that trannie, it is silicon, not germanium? And all trannies are spec'd as germanium on the schematic. Out of interest, trannies X1, 2, 3 and 4 are all this type of package. 5, 6, 7, & 8 are can types. Maybe in later versions of this set those four trannies were changed to silicon ones?

As already mentioned, the emitter resistors for X3 and X4, R8 & R12 are 300Ω and not 470Ω as per schematic - does that have any bearing or make sense even of the trannies being Si not Ge?

[PJL]

As it appears this is a silicon version, many of the resistor values will have changed and the current/voltage information will all be wrong.

Can you try measuring R2 again as 0V is not possible although it maybe that your meter can't cope with the RF injected here by the oscillator.

Have you changed the electrolytics as these maybe responsible for motor-boating? Readings will not be reliable whilst it is unstable.

[Goldieoldie]

Just stating the obvious, have you checked the pin outs on your replacement transistor are correct?

[stevehertz]

Some progress. I discovered that a lead on X4 was severed, rotted through somehow, although like X1 (that also had a severed lead) it was covered in a dark rubbery glue. Replacing X4 with a silicon MPSH10, I can now, ha, just about, with the deft touch of a brain surgeon, tune in to a single strong station. However, when I say tune in, you can barely hear it, it is hidden behind a motorboating sound. But nonetheless, progress.

Still confused by:

Are X1 to X4 silicon trannies - see previous posts?
There is 6.5V dropped across R9 - does this seem correct?
The emitter resistor voltages on X1 to X4 are still all way out.

[Andrewausfa]

X1,3,4: 2SC73 Ge NPN, 2SC75 Ge NPN & 2SC76 Ge NPN.

Andrew

[Station X]

If the junctions of the removed transistor have survived they can be tested using the diode test function of a DMM. A forward volt drop of around 0.2V would denote a germanium transistor, 0.6V a silicon transistor.

[stevehertz]

Originally Posted by Andrewausfa

X1,3,4: 2SC73 Ge NPN, 2SC75 Ge NPN & 2SC76 Ge NPN.

Andrew

Yes, that's what it says on the schematic, see post 32. In fact, X1, X3 and X4 are all marked C403. Not sure about X2, can't see its face, but it's the same package so I'd bet it's also a C403. Now, you generally add '2S' in front of 'C' prefixed trannies. And guess what? A 2SC403 trannie is silicon. That's the conundrum. So, schematic says Ge, actual fitted trannies appear to be Si.

I reckon the trannies were upgraded to silicon during the production run of the set.

[ms660]

A change to silicon wouldn't be unusual, move on a year or so to the Sony 2R-26 for example.

When I worked for Sony all the manuals were supplemented with modification/changes sheets as needed, these have rarely survived in the internet world of service data.

Lawrence.

[stevehertz]

Update.

The actual transistors in the set are, X1, 3 & 4: C403 (2SC403), X2: C401 (2SC401).

They are silicon, I tested one and it has a forward volt drop of 645mV.
The AF output trannies (X5, 6, 7 & 8) are in cans and I presently have no reason to remove one. The sides of the cans are not visible due to them being tightly packed.

I have now discovered that the PCB and components are not exactly as per the schematic. Indeed they wouldn't be if the trannies are Si not Ge. So that could explain why the measured emitter voltages do not tally with the schematic, the bias resistors are different.

I removed X2 to test it and although it seemed fine in a transistor tester I exchanged it for another MPSH10.

For some reason the set seems a bit more co-operative now. I can tune in to a strong station. But here's the weird bit. The motorboating sound is affected in two ways; the the frequency of the 'beat' slows down when a station is tuned, and it also slows down when you rotate the set for strongest signal. So with judicious adjustments of those two I can get a strong station to tune in without any motorboating. That must tell us something surely? AGC problem?

[Goldieoldie]

Check the caps. As I've said before you can just bridge them to see if it makes a difference.

Motor boating is a classic sign of cap failure.

[vinrads]

It's almost certain to be the electrolytic capacitors causing the motor boating, low volume etc. as I said, I would have replaced all the electrolytic capacitors before looking for other faults, some will not like this idea, having repaired a hundred or two this is what I do.

Mick.

[stevehertz]

Thanks guys. I'll go down the electrolytic route. As anyone who has worked on these miniatures will know, every component is literally crammed in side by side. There's also a subminiature tuning dial string to avoid when desoldering. It can take 20 minutes to remove one component and always the chance of lifting those tiny PCB tracks. I have to work in short sessions as patience and eyesight are sorely tested.