Please don't ban me!

[boater sam]

Another really long shot coming up.

Despite my better judgment I have bought the horrible 1990s Spirit of St Louis  Sparton  radio  LW-119 Bluebird 566.

Its a Chinese 2 chip and 2 transistor MW, LW, & FM pcb.

It works on Medium wave fine, LW will need the aerial coil on the ferrite  sorting after the 13A plug has mauled it. The FM is non-existent other than an AF amp hiss.

Damaged because the back is missing and someone coiled the mains lead, including the plug, and slung it inside onto the pcb.

Now the 64,000 dollar question. 

Does anyone have any circuit details so that I can try to magically fix it?  I would not normally bother but these are so unusual that I rather like it.

Please have sympathy with this demented fool and try to help me.   Please.

[peter scott]

Perhaps the chip numbers would lead you to application notes??

Peter

[ppppenguin]

1992 is 30 years ago! So it's sort-of vintage.

[boater sam]

Perhaps the chip numbers would lead you to application notes??

Peter

Brilliant idea, I will find my loupe and try to read them.  Why did I not think of that?
What do I do if they are all in Chinese?

[boater sam]

1992 is 30 years ago! So it's sort-of vintage.

I was wary of putting this request in the vintage forum.   Should I get it transferred?  Will I get shouted at?

I know its really Eastern rubbish but it looks outstanding. The original 1936 radio was a masterpiece or cramming valves in a small box and the art deco design was on the money.

One of these was sold on Etsy for £214.

[peter scott]

What do I do if they are all in Chinese?

Take a photo and use a character reader then use Google translate.

Peter

[boater sam]

[boater sam]

Not a good day.


Amp chip is KA2201, straight forward and I know it works because MW is working.

Other chip is    (blank, blank blank)         16pin DIL . That is all I can find about it, no markings at all.  But it must work as MW is working.

LW is obviously never going to work with the aerial coil all chopped up. I have tried to identify the connections, to find the broken ends, to establish what the 4 connections do.

But defeated.  There are several turns of extremely fine wire cut and displaced. All waxed heavily.

The connections are made with 2, 3 and 4 strands of wire twisted together to the pcb connections, a bit like constructed Litz wire. 
The winding is roughly pile wound with more than 1 , 2 or 3  strands wound simultaneously so it is impossible to unwind any part as it is all knotted together. I thought it would be just 2 coils but so far I cannot identify a single winding.
Having tried to find the breaks I now have 11 ends, and none of them give continuity to another. Unbelievable.

So without knowing the circuit I cannot reconstruct a LW coil.

As to the FM VHF that is another unknown. It looks like 2 transistors feeding into the rest of the AM circuit around the chip.

Bit of an impasse.

If all else fails I may construct an AM/FM/DAB chassis to fit inside the radio using the existing control knob positions.

[Mike Watterson]

If it has a tuning cap (mechanical or varicap) two wires may be for that.
Probe PCB where you think wires may have attached with a 2m+ long wire while powered on to LW. Possibly 20 t coil feeds that.

It's also possible the coil was made / designed for a transistor or low impedance RF input on IC, which would use 3 connections, one being a tap at 10 to 30 turns for RF in and the entire winding for tuning, but that actual radio only needs a 1mH approx tuning coil. Try the main winding of other LW ferrite rod coils.

Does it use ceramic filters for FM & AM as well as capacitive tuning (mechanical or varicap)? If so look at 16 pin AM/FM radio ICs. Otherwise it's DSP based.

[boater sam]

Thanks Mike.

DSP based?  I know nothing about.  Is there a 16DIL chip that is often used for these junk radios from China?

The long wave coil had 4 connections.  3 went onto the pcb, one onto the tuning variable capacitor.

Now the nightmare.

One coil connection is made up of 3 strands.
Another is made of 2 strands.
The other 2 are one strand each.  I think, hard to be sure, the damage is severe.

So I cannot say how many coils are in the winding or where the starts and ends are/were.

All but the first with 3 strands are disconnected by breaks within a few turns in the coil winding due to damage. They fell away as I tried to find the ends of the breaks.
I am now left with lots of ends of windings, none of which will unwind as they are all knotted in with the remaining windings. It looks as though the coils were wound all at the same pass rather than one at a time, the whole coil is just a jumble of intertwined fine wires. I cannot fathom any continuity between these ends.

Without a circuit it is beyond  me to try to reconstruct this coil. If I knew how the windings were connected I could wind a couple of coils and play till the inductance was correct but I have no clue what the original was like.

Any help or suggestions gratefully received.

Sam.