Circuit Diagrams in "The Screwdrivers Experst Guide"

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3pinplug
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Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by 3pinplug »

Hi all

The two circuits shown are in Lou Franklins book the "The Expert Screwdrivers Guide", I have built both of these so far on a small piece of perf board wiothout any success. Firstly, can i ask if anyone else has ever tried buidling these and if they worked?

My dilemma is the same on both boards I have +12v at the switch but then only around "0.70V" up to one side of the 20pf trimmer, then only 2.76V on the far side of the crystal - is that right???

Looking at this circuit these values strike me as very low. I have no oscillation on either of ther crystals and have jhad this on both boards with siumilar valiues being obtained on both boards, I am wondering if this is due to the low volatages. I have shown in the pics on the circuit where I have cut the track and replaced the tripled 5.12mhz signal with the crystal 15.360 & 15.810 signals (as per the book i believe).

Anyone shed any light on this for me?

Thanks.
circ4.JPG
circ3.jpg
circ1.jpg
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by Otter »

On the third drawing where it says "TO OSC" the circuit is expecting a Colpitts oscillator circuit. The output of the Colpitts oscillator will go to the 15.360 injection point.
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by Otter »

The 0.7V on the anode of the diode that's switched on is correct because that's the forward voltage of the diode. As long as the diode is turned on it should provide a path to ground to enable the crystal to oscillate.
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by cb4ever104 »

I don't have that diagram in my book. Mine is dated 83 USA and 84 Europe. Yours might be a later edition ?
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by cb4ever104 »

Otter wrote: 31 Jan 2022, 09:20 On the third drawing where it says "TO OSC" the circuit is expecting a Colpitts oscillator circuit. The output of the Colpitts oscillator will go to the 15.360 injection point.
Ditto what Tim said . I haven't looked , but I'm assuming that design is similar to what's used on the small pcb that's found in the Madison etc to make it 80ch.
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by 3pinplug »

Hi

Thank you for the information, will try and answer the above:-

Otter - Yes it does go to the oscillator if i have fitted it in the right place, that's where the 2.76V is coming from. I have fitted it to Pin 4 of IC202 as shown in the above schematic and cut the track at the point indicated, I still have the 5.12 x 3 (15.360)mhz signal below the cut.

Otter - How can I check if the diode is turned on, god did I really just ask that! - Hahaha!

Cb4ver - The book says "new international edition" in a star on the front cover, can't see a date anywhere else in it, where did you find the date in yours and I will check to see what mine says? The diagrams are in a number fo appendices at the back of the book covering:-

Appendix A - Basic frequency mods for PLL Radios
Appendix B - PLL conversion using the crystal exchange method.
Appendic C - Frequency mods on rom controlled PLL's
Appendix D - Unlocking the clarifier make it track transmit too.
Appendix E - AM to FM conversions made easy

My crystals are not giving anything its as thouigh they are off, anything else I can try. Where is shows earth on the board I have this connected to ground on the PCB itself. I still have o.oov onojne side of the 20pf trimmer, is this right?

Thanks again for all the assistance to date.
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by cb4ever104 »

Hi 3pinplug .

What radio are you fitting this in to ?

As Otter said , the output of this circuit has to be fed into an oscillator before it goes anywhere . The circuit you have attached has an IC (202) shown . This isn't an oscillator . The crystal won't do anything by itself .

FYI . If you have 0.7V on the anode of those diodes , then they are "on" .

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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by cb4ever104 »

Just to add . Here's the Madison cct . It's not 100% clear , but you don't need to see the full details .

This is the little pcb with the 2 crystals . Similar to yours . It gets switched from the button on the front panel (HI/LOW)
Mad_1.JPG
That then gets fed to this first transistor . Can't read the number . Might be TR30 . You can tell it's an oscillator with the feedback between base and emitter . It then goes through TR29 and out through the tuned cct .
Mad_2.JPG
Hope this helps .

S.
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by 3pinplug »

Hi
Heres the schematic, its for a sharp cb4470.

I have been following the diagram / text in the other pic from the book hence why I injected the supposed signal where I have, if this is the wrong point on the schematic can you confirm where it should be as sounds like i am in working in the wrong place.
Thanks for the help!
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by cb4ever104 »

You're injecting in the right place. You just don't have a signal to inject. At the moment your radio internally generates the 5Mhz signal , which then gets trippled. You'll need to build a small oscillator circuit to generate your 15Mhz signal. Similar to what I posted on my 2nd image. All you have built is a switching circuit. You need the oscillator part. Once you have that then you can feed it into your IC. Hope that helps.
Last edited by cb4ever104 on 31 Jan 2022, 13:38, edited 1 time in total.
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Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by 3pinplug »

Hi Cb4ever

thank you ever so much for your patience, think it has clicked, well almost!!!.
I have just seen the diagram below in the book and from what you are saying i think i have missed this, to be honest there are 4 diagrams, three which I will call 'switch diagrams' which is what you are saying i have built and thisdiagram which is an "outboard external oscillaor" and what I need. So I f i build this in theory it will work.

Can I pick your brains once more, so I build the oscillator but it only has 1 xtal, if i want to use Xtals do I simply build the board and inject my exisiting board where it says "to osc" at the base of the the transistor shown in the diagram below? replacing the single xtal / trimmer shown?
osc board.jpg
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by cb4ever104 »

Correct. You already have the switch. So take the output that says "TO OSC" in the bit you've built and use that to feed into the "XTAL" part , or base of the transistor in the image you posted. You don't need that additional 20pF trimmer , as you already have them in your switching circuit. You can set them up individually once you get it up and working.The "RF OUTPUT" will go to your IC.
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Radios ....? Anything that says "TAIWAN R.O.C" on the back.
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by 3pinplug »

I will have to order a couple of parts but will definitely let you know if it works, once done.

Thanks again for your help, CB4ever you are a legend!!
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by cb4ever104 »

No problem m8. Hope you get it working. I like doing that kind of stuff too. All part of the learning curve :thumbup:
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Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
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Re: Circuit Diagrams in "The Screwdrivers Experst Guide"

Post by 3pinplug »

Need to add some more capacitance to the VCO, in the diagram below can I just check i am reading this right:-

D202 is VCO varactor and its capacitor C216 I need to increase the value of.

I recall doing this once in the past but can't completely remember the process / how to identify the relevant capacitor to increase- think its called a senior moment! :?
vco.jpg
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