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Help with an old circuit diagram, please? Answered

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Remember my inductor thread?

Well, I'm getting closer to my project. The bulk of the device is to be based around an old transistor radio. I've got hold of one (a Phillips D1018/05, if it helps).

Wonderfully, I opened the radio to find it has the circuit diagram stuck inside the back cover.

Unfortunately, it's only half an inch high, so, I've scanned it.

Now, I have a problem:

The directions I am working with are vague:

Try removing the Ferrite tuning coil and then replacing it with (another detecting component which I have, but if I name it the surprise will be lost) with a 12mH inductor connected in parralel.

Spelling aside, I was happy with this, until I opened the radio and found that the antenna has four wires connected to it.

So, I need a few answers:

  • In the circuit diagram, which part is the ferrite tuning coil / antenna? I think it's part of the bottom-left corner of the diagram, but I need to confirm this.
  • The four wires all disappear through the same hole, but one is stained blue and one red - which ones should I be dealing with?
  • The component I am replacing the coil with is polarity-sensitive. The vendor was very careful to indicate the negative electrode - which way round should I connect it? I think I need to connect the negative of the component towards the bottom lead of the circuit diagram, but I want to make sure before I kill the component.

I know these are potentially-noob questions, but this is my most expensive project so far, and some of the parts required subversion to acquire, so I don't want to mess it up.

(If there's anything I've forgotten to ask / say, please let me know that as well. I'd rather not reveal the nature of the final project; it's not for a contest, but there's nothing like it on the site yet. If useful advice depends on knowing what the component is, then I will reveal it, but I'd prefer not to spoil the big unveiling.)

16 Replies

user
Normjr (author)2009-09-11

Is it possible to get a larger, clearer image of the left (Input) end of the diagram?

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Kiteman (author)Normjr2009-09-11

Not really - that's a scan of an original that is only half an inch tall.

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Lithium Rain (author)Kiteman2009-09-11

I'm assuming the project is long-dead anyhow?

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Kiteman (author)Lithium Rain2009-09-11

I prefer "in a long term hiatus".

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robomaniac (author)2008-07-06

I love reverse engineering!

Here are circuit that look the same, these are radio circuit.

http://people.msoe.edu/~reyer/regency/schematic.jpg

http://www.ibiblio.org/kuphaldt/electricCircuits/Semi/03453.png

You read circuit like you read a book, from left to right.

The antenna is the coil with the 4 wires. The one you have circle in the schematic.
If you look closely. Use in Firefox3 Ctrl and + to zoom.

4 wires and 2 are connected to ground. One is going to the capatic

Do you have to remove the ferrite tuning coil to replace it with your magic component?

You need to place you magic component before the capacitor and then to the transitor. One wire goes there and the other one goes to the ground.
look here
http://people.msoe.edu/~reyer/regency/schematic.jpg

You remove the L1 and forget about L2 and C2. Your component will go to the ground and to C1

You need to turn the PCB around and use the multimeter.

I suggest you start the instructable and add only these pictures and make it collaborated so I could tell you whre to put your prob. You write a gimmick title and upload the picutres and the schematic I gave you. Then we will be able to work together.

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gmoon (author)robomaniac2008-07-06

I don't read it like that at all. The antenna coil is the two-part inductor (connected to Q1 and C2, with the long line--the common core.) It corresponds to L1 and L2 in the ibiblio schematic, but isn't wired the same.

Kiteman's comment box only encloses half of the antenna coil.

4 wires and 2 are connected to ground. One is going to the capatic

In the ibiblio schematic the split antenna coil may be connected to gnd in two places, but only one lead of the antenna (T2) in Kiteman's schematic is. L2 corresponds to the top winding of T2. For kiteman's, one end is connected to the collector of Q1, and the other to the next inductor in the signal chain.

The placement and operation of L2 (1/2 of T2) is fairly different between the two circuits.

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Kiteman (author)Kiteman2008-07-06

Done - you're a collaborator now.

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OracsRevenge (author)2008-07-06

I would say that your best bet is to get to the other side of the board with a multi-meter and double check where everything connects. You never know, the text at the bottom of your schematic may be correct "subject to change without notice" !!! Once you have confirmed the circuit diagram and all the main components, you will be in a better position, but I would imagine you will be trying a little trial and error with this one as there are many different methods of implementing the tuner stage. An idea might be to post a question on an amateur radio forum. I have found and looked through the original information you refer to for this project, have you tried contacting the author directly?

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NachoMahma (author)2008-07-06

. It's the inductors between the capacitor gangs. The ganged capacitor (tuning capacitor) is the dotted line. (The dotted line on the right side is vol/on-off) . Dunno. Looks to me like you will need two of your widgets. . Negative is on the bottom. See how it connects to the "skinny" side of the battery symbol? . Verify all that before applying power. I don't understand radio circuits very well.

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NachoMahma (author)NachoMahma2008-07-06

. Oh! Looks like your red/green wires on on the left inductor between the gangs.

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Kiteman (author)NachoMahma2008-07-06

> That's the squiggly line near the middle of the box I added? Just above the resistor? > I should only need one widget, according to the instructions. > So... you're saying I can ignore the two uncoloured wires, and connect my component between the points where the coloured wires go?

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NachoMahma (author)Kiteman2008-07-06

. The inductor on the left side of you box is one of the tunable coils (square silver cans with screw slot). The inductor on the right (next to C2) is the antenna, coupled via ferrite to T2 above. . . Looking at the schematic closer, that is probably right. I'm not real good at this. Take all of this with a grain of salt. . . I'm lost on this one. I thought the RED/GRN labels belonged to the antenna, but closer exam looks like they go to the tunable coil. I'll guess that the antenna section will have greater resistance than T2, but I don't know what function T2 serves. . . Maybe someone that knows what they are talking about will show up soon.

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gmoon (author)2008-07-06

Looks like the antenna loop inductor is T2 (right side of the boxed comment, and above.) The two windings share one core. Maybe T1 is the red-colored inductor on the board? I'd try to trace the inductor wires on the underside of the PCB.

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guyfrom7up (author)2008-07-06

I think the bottom left corner may be a filter, I can see 2 tank circuits controlled by 1gang capacitor

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