Pocket radio repairs

[lightning]

Having now collected over a dozen of these small radios, l have one or two with issues that l want to have a go at repairing.

These type of repairs are new to me, but l may as well start somewhere. First off l have a lovely 1960 National Panasonic pocket radio, it's in beautiful condition and came to me not working.

I found that a tiny bolt had lost its nut, this bolt formed the connection from the on off switch and also held the aerial in place.

So now it works but sensitivity is poor. It receives Radio 5 loud and clear but not much else. l can receive a music station towards the top of the MW band but it's distorted.

What might be the cause of this? lt's very well made but obviously not easy to work on because the components are tightly packed around the PCB.

What about replacing all the electrolytic capacitors, is that worth doing? l assume all the resistors will be fine, and the disc capacitors are fairly reliable l believe.

Also l've resisted attempts to tweak the IF transformers with their tempting screw adjusters in the top.

As the circuit board is mounted component side down, and quite tricky to get out, these look untouched by previous owners fortunately.

[vinrads]

I would change all the electrolytic capacitors, note their polarity it's not always obvious, don't bother checking them and keep on resisting the tweaking.

[Nuvistor]

Don’t replace anything without some testing and proper fault finding. What test equipment do you have?
If you don’t have much experience with fault finding then the transistor section of this web page may help.
https://www.vintage-radio.com/repair...ion/index.html

[lightning]

That page is very useful, thank you.
l will have a proper read of it later. l don't currently have any radio specific test equipment, only a Fluke DMM

[vinrads]

I speak from years of experience when I said replace the capacitor ,you can fault find all you like , but at the end of it all you will have replaced all the electrolytic capacitors , a test meter is not much use for testing if a capacitor has gone low in value , all voltages will read ok . I have at least seventy transistor radios in my collection, all repaired . it's just the same as replacing the wax capacitors in valve radio's I replace them on block , why waste time when you know what the fault is going to be , replacing the capacitors is good experience in itself . whatever you do good luck with it . Mick.

[stevehertz]

Pocket radios can be very hard to restore even for the experienced restorer. I too have recently started a collection and have had a go at a few sets. The amount of room you have to work in is next to nothing with components mounted on end and literally side by side, and there's often a nylon cord just waiting to be burnt through with a soldering iron. If you can get hold of one, schematics don't always tally with what you've actually got etc etc. Lots of problems and issues. I have restored old video machines that require working to within microns, and pre-war TV sets that are themselves another chapter, but I reckon palm size portable radios are amongst the most difficult to work on. But they are nice things!

[Craig Sawyers]

Thinking back many many decades to when I was at school, one of the lads asked me to repair his transistor radio. Fine, I said - I'll have a look.

Well, as others have said, this sort of thing is a nightmare. In this case the problem was the circuit board layout had been done with microscopic track width. And what had happened is there were multiple, invisible cracks in these tracks. Using my little multimeter I quickly found five or six open circuit tracks, and there were clearly more to be found.

Impossible to reliably fix, so I gave it back and told him that it was unfixable and why.

I've never felt the need to delve into the rabbit hole of collecting and repairing these miniature radios.

But good luck!

Craig

[shadoman]

I've just finished repairing five pocket radios which I bought as as a job lot.These included Hong Kong and Japanese made radios ,one being a nicely made Japanese philco. In every one changing the electrolytics brought them back to life. I did check each one out of interest and out of about 16 caps only two were still good. I would change all the electrolytics and go from there.

[lightning]

Well, l've got on to it this afternoon and replaced four 33uf 3v capacitors, all measured over 100uf on my meter.

Then l moved on to the smaller ones, the first was a 10uf which read 0.5uf, so l changed that. The next, 0.47uf read 1uf not too bad but replaced anyway.

There are two others but they are under the tuning cord and would need that dismantled to get at.

Anyhow, l tried the radio after replacing the above parts....exactly the same. Very good on radio 5, poor sensitivity and distortion on the higher frequency stations

Best get the other two capacitors replaced l guess. l've got a similar radio made by Magnavox and that is superb compared to this one, picks up loads of stations and no distortion on music, so l know what it should be like.

[Nickthedentist]

This seems to be one of those rare situations where blanket re-capping is a really good idea.

[ChristianFletcher]

Just out of interest have you checked for stations with a known good radio. My MW reception is pretty bad at the best of times and all modern equipment in the household cause an incredible amount of interference. Your radio almost certainly need some repair but also some sets just aren’t very good today. Get stuck in your going to make mistakes like the rest of us do but don’t worry it’s only a radio

[stevehertz]

A tip I learnt on here is to loosely wrap tuning cords with aluminium foil to help protect them should a soldering iron come into contact.

[lightning]

l've spent pretty much the whole evening replacing the rest of the capacitors on this radio, fortunately the tuning wheels and cord come off without disturbing the cord.

The three remaining capacitors were 10uf, 10uf and 0.5uf
Measured 0.6uf, 0.6uf and 1.2uf when removed

After re-assembly the radio isn't much better really, it's louder, in fact R5 in the middle of the band is almost too loud, at the top of the band it's distorted, and at the lower end there's almost no reception (compared to a similar radio)
Sensitivity is still poor.
Also if you turn the radio round, so the aerial isn't aligned in the best way, even the strong station disappears completely.
Well at least it works. But l would like to get it working properly!

[stevehertz]

Even strong stations will disappear if the antenna is at right angles to the transmitter, perfectly normal.

[vinrads]

Hi well done replacing the capacitors ,a fiddley job I know , would you say the stations are in the correct position on the dial, what do you mean by distorted ? Mick.

[lightning]

Any ideas as to why stations at the top of the band are distorted? With music it's difficult to actually identify what's playing.

Similar radios l have are fine, as well as AM can be anyway but perfectly useable.
l've just bought another one of these radios "untested" hopefully l can get one good one from the two.

[Herald1360]

That cord drive assembly is an impressive bit of engineering to find in a basic pocket portable! More common is just a calibrated edgewise knob screwed directly to the cap spindle.


I wonder if your loud signal OK, quiet ones distorted could be simply(?) a problem with a scratchy misaligned speaker cone or output stage quiescent current / mismatched transistors?

[vinrads]

When listening to a distorted station is it loud and distorted , I am wondering if the agc is working , Mick.

[Nuvistor]

Well done on getting those capacitors changed. Mick and Chris have good suggestions for what could be wrong.
What is the station that is is distorted?
I wonder if the detector diode is faulty, ok on strong signals but cant cope with weaker ones.

[Restoration73]

The wires to ferrite rods can be vulnerable. When you tune the set to a high frequency
ca 1500kHz, the aerial trimmer at rear of the tuning capacitor should peak the signal,
and on the lower end ca 600kHz sliding the coil on the rod should also peak it. If not
check continuity of ferrite rod coil winding.