SONY Transistor Radio - Identification?

[DonaldStott]

Can anyone help with the identification of this SONY Transistor radio - it has lost it's label from the back of the case:-







No value in it at all but just using it as a test and educational project - there is no FM!

[Cobaltblue]

Sony Radio TFM-7050W ?

Cheers Mike T

[ms660]

https://www.radiomuseum.org/r/sony_f..._tfm_7040.html

?

Lawrence.

[DonaldStott]

Thanks Mike T and Lawrence - that was quick!

All I need to do now is find the schematic - it's not on my Service Data DVD?

[ms660]

The latter's here:

https://www.service-data.com/section...528/1/tfm-7040

Lawrence.

[DonaldStott]

Obtained the circuit diagram but would really like a schematic showing the actual components on the board - anyone?

Still finding my way around transistor radios …

[Nickthedentist]

Don’t overlook the fact sometimes, no such thing was ever published.

Taking good photos of both sides of the boards, reversing the track side image, then working out what’s what and writing on the component numbers yourself can be the only way to do it sometimes, and is a really good way of familiarising yourself with the set too.

Here are two snaps taken on my phone of a bit of BT equipment:

[DonaldStott]

Originally Posted by Nickthedentist

Don’t overlook the fact sometimes, no such thing was ever published.

We can but hope that something might exist somewhere?

Originally Posted by Nickthedentist

Taking good photos of both sides of the boards, reversing the track side image, then working out what’s what and writing on the component numbers yourself can be the only way to do it sometimes, and is a really good way of familiarising yourself with the set too.

Taking lots of pics is part of my standard procedure which has saved me on numerous occasions! Here are pictures of both sides of this SONY Transistor PCB - wish me luck! :-



Two quick questions though?

1. What are these components filled with black goo:-



2. What are these black filaments across several components - just stray black goo or actual connecting wires:-

Originally Posted by Nickthedentist

Here are two snaps taken on my phone of a bit of BT equipment:

Nick - it's only on very rare occasions indeed that I've come across such a well labelled and organised PCB!


The set works on AM but not FM so (stating the obvious) the problem is almost certainly in the FM front-end but remember the set has no value and it's being looked at as a test/educational project i.e. a bit of fun!

[Nickthedentist]

Yes, points taken

In my case, I was trying to create a circuit diagram from the well-labelled board. In yours, I was hoping that you could make a component layout drawing from the circuit diagram.

(1) I would guess that they're the audio output transistors, secured into their heatsinks with the goo,
(2) Nothing more than strings of goo! Similar to what you sometimes get when using a tube of UHU or Evo-Stik etc.

Have you given the AM/FM switch a good clean?

Good luck,

Nick.

[Graham G3ZVT]

The last time I encountered an audio output pair with that black mastic, there was a tiny bead thermistor embedded in it. I didn't notice the fine wires going to it so consequently I damaged it.
This was a portable TV set, but come to think of it, also a Sony.

[DonaldStott]

Originally Posted by Nickthedentist

Have you given the AM/FM switch a good clean?

Thanks Nick

Well that was quick - gave the AM/FM switch another squirt of Servisol and FM is miraculously restored and working! On the bench power supply at 6V it's drawing just over 20mA which seems ok?

As it's a test project I'll do some general voltage testing, transistor measurements, change electrolytics and give the case a bit of TLC - unfortunate that the back label is missing?

That's about it as I go off and try to familiarise myself with the PCB layout, comparing it with the circuit diagram - not my strongest suit but I need the practice?

[Nickthedentist]

Well done! Always worth doing the simple stuff first before getting too stuck-in

As this is an "educational project", don't just change the electrolytics en masse. Do you have an ESR meter? Even if you do elect to change them, it would be interesting to check the removed ones and see if they really were below-spec. or not.

They may in fact be all fine. Japanese electrolytic capacitors are not renowned for going faulty, especially in a battery-operated radio in Glasgow! It may be a different matter in a hot-running circuit (e.g. power amplifier or power supply) or a set which has lived in a very warm climate, of course.

Sometimes, especially with cheaply-built compact gear like this, changing bits on spec can sometimes result in damaged tracks etc. introducing trouble where there wasn't any before.

And be careful with your voltage measurements... a slip of a probe can short adjacent pads together, which can cause extensive damage if you're unlucky. We've all done it! Slipping some sleeving over the metal part of the probe so that just the last mm is bare can help.

[DonaldStott]

In the interests of completeness does anyone have a high-res image of the label on the back of this SONY TFM-7040 radio?