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UPD2824 talk

Discussion in 'CB Radio Modifications' started by loosecannon, Mar 16, 2019.

  1. loosecannon

    loosecannon Sr. Member

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    I have been restoring a President AX-144 lately, and that usually leads me to stare at schematics in order to gather ideas on possible upgrades or mods i might like to try out.

    yes, there is more mod info out there for this board than most others thanks to our friend Handy Andy, and Andy just let me say that all your past work is still appreciated.

    one of the main things Andy said that i picked up on was just how many different versions of this board there are, and with that how different each version can be from others.



    There are SOO many differences! some versions have mike gains, some don't, and even the ones that don't have mike gains differ from each other in the mic circuits.

    then you have parts in the radio that aren't the ones listed in the schematic for your particular radio.
    for example, TR25 and TR26 are mic amp transistors.
    every schematic i looked at showed TR25 to be a 2SC945 and TR26 to be a 2SC1312 (might have that number wrong).
    in my AX144, they are both 2SC1312.
    i know, not a huge difference but it does illustrate how difficult it can be to decipher just what you do and don't want to mess with inside one of these beasts.

    SO!
    I stated all that just to get it out of the way that just because something is being discussed in this thread as a mod to a UPD2824 SSB chassis, that it may or may not be something you want to do to your particular radio.

    I also want to keep this very specific in order to keep the posts short and to the point.
    again, these stories have mostly all been told already.



    To start, i would like to look at R501, which is a 100 ohm resistor mounted on the mic jack PC board, OF SOME MODELS!

    it doesn't seem to be there on the PC122 versions.

    so, why is this resistor there?
    is it just to guard against high volumes on power mikes?
    is it there because it was cheaper than putting a coil there, and hey, it's a wire wound resistor!

    does anyone see any benefit to replacing it with a jumper and a ferrite bead?
    i can't imagine that 100 ohms is having much effect on mic audio level, but that again begs the question of why it's there.

    maybe i am missing what it's purpose is.
    LC
     

  2. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    The idea of having the wirewound 100 ohm resistor inline with the audio path is that it can suppress RF from getting into the audio path and making its way to the mic audio amp, where it could cause all kinds of havoc. If it's a wirewound resistor, I'd leave it there, as it does serve a purpose. I don't know why more models didn't implement this, to be truthful.


    ~Cheers~
     
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  3. loosecannon

    loosecannon Sr. Member

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    thanks for the verification Xit!

    I just had this feeling that the wirewound aspect was an important one.

    Right now i am looking at the AM modulator section, and since it is basically identical to the old galaxy style modulators (because galaxy copied this design so obviously), i am going to change out TR43 and TR44 for a TIP42 and a TIP36 respectively.

    just because it's something to do.
    LC
     
  4. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    There are some other scenarios too...

    Note it's location in the circuit.

    For the rest of those technically curious...
    MicJack.jpg

    They placed it IN SERIES with the Mic gain, so the Mic Gain pot, being what it is,, when you use it's full rotation - it doesn't pass all the current the microphone has to give. Why? Well, a power mike can blow the substrate on the Mic Gain (yes there is that much power possible) so they placed a dropping resistor and use it as an RF choke. It limits current for a reason. Mostly for the Mic Gain control itself.

    • Sure there are Tonal and Voice level quality issues, but these things are setup for "most scenarios" - if you wish - CHANGE IT! Just don't be surprised if problems develop.

    Wirewound offers a level of choke and provides current limiting on the source side of the pot, not the ground or wiper side. That way, if you have static, a poke can shoot thru and into the Mic gain pot. although not a big deal, you do have mics out there that are dynamic that share case to shield - which means if the operator is at one potential - the radio can operate at another - hence the Positive Or Negative Ground issue these things have. To provide some current limiting and RF choke in one package may sound like a cheap way out - but it does work.

    Now, I'm not the guy that built this radio, but from my own repairs of similar setups, blown mic pots are rare but not impossible. I've seen D104's pop open the substrate from people that mod these things. (Pic available on request...) Poor Amp shielding and RF burns from the operators - can also wreak havoc on these too.
     
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  5. loosecannon

    loosecannon Sr. Member

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    thanks for the reply Andy.

    i'm going to be leaving it in place.

    I think im going to do the assymetrical modulation mod to it, but im going to use a trimmer in place of the resistor initially so i can set the negative peaks right where i want them and then measure the resistance.

    this is how i usually do it when i do that mod.

    I upped the value of C118 from .047 to .1, and i think im going to up C129 just a tiny bit also.

    the next question is why did they use only a 330uF cap for the output coupling of the audio amp?
    i would like to try a 1000uF there unless someone can see a reason why it would be a bad move.
    LC
     
  6. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    I used to up the auntie on that for those that liked to use external "stereo" quality speakers to get home-sound for better fidelity of the receive audio (which is why those other mods are inclusive with this) - but as you will find out the STABILITY of the audio amp is the one in question.

    For as you raise the uF values, so does it's bandwidth. This then equates to lowering of impedance expected. You may start out limited bandwidth - but as you open up that throttle thru using larger value caps, the expected impedance drops - quickly - past 470uF - to less than 2 ohms - generating an instability issue.

    The typical AM only types used a range from 0.22uF (224) ~ 0.1uF (104) to as low as 0.047 (473) as well as an ohmic value of 1 ohm to 2.2 ohm to "balance out" the bandwidth to an expected impedance - and putting all of this in with-and- thru a Reactance Modulator or Speaker - both are inductive and can generate an EMF (EMP more likely) due to the mis-match - the Inductance is fighting against the extra bandwidth and high-frequency rolloff filters usually solve this.

    So the use of Cap resistor combos to reduce bandwidth to match impedance better and keep the inductive reactance in balance - much like tuning of coil - a cap can be use to "sharpen" as well as change the way the skirt appears to the next stage as well as unto itself in regards to imbalance and frequency response issues around bandwidth.
     
  7. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Compare the uPD 1182 to say a uPD 1242 and you'll see what I mean...
    UPD1182.jpg

    Although essentially the same, Note pin 3 and the "bootstrap" value and type it is...

    Now equate that to the output cap values...

    In the PC122, R166 and C123 are used to improve the bandwidth...
     
  8. loosecannon

    loosecannon Sr. Member

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    well ive got the ol' girl re-capped and all the corrosive goop out of it, and upon firing up the radio, i found i had no modulation in any mode.

    checked PA, works great.

    looking at the way things are routed in this chassis, it seems like the PA circuit doesn't use the same mic amp circuit as the radio does.

    now, knowing that i had to take basically the whole mic amp circuit out in order to remove the glue that was so generously applied all over that section, i immediately looked here to find my problem.

    and after a few exhaustive hours of studying diagrams and pinouts i have come to the conclusion that not only does my personal AX-144 use a 2SC1312 instead of a 2SC945 for TR25 (none of the different versions of this chassis that i have seen show this transistor there, but it does make sense to use one)

    Then, i find out that there are two different pinouts to the 2SC1312!!!
    one version is the ECB that we would expect, and the other?
    well its a BCE of course.
    looking at this diagram and specifically C115 that connects the bases of TR25 and TR26 together shows that the 2SC1312's used in my radio are indeed the BCE versions:
    http://www.cbtricks.com/radios/uniden/ax_144/graphics/uniden_ax_144_sm_pcb_layout_pg18.pdf

    so it looks as though i put TR25 and TR26 in backwards from the way they would have been originally.

    now i have to wait until i get home tonight to find out if any real damage to other parts was done by my oversight DOH!

    i will probably also have to find a couple of 2SC1312's now.
    yes, i can use other transistors, but if i can find some, i'll use what was in there.

    oh well, live and learn.

    now im off to find out which transistor is responsible for the channel muting between selector positions and get rid of it if possible.
    LC
     
  9. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    LC810MicAmpCompare.jpg
     
  10. loosecannon

    loosecannon Sr. Member

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    it's working normally now.

    i had indeed installed both TR25 and TR26 backwards because they were originally installed opposite of the silkscreen on the board and i didn't pay close enough attention when i pulled them.

    TR26 was blown open, but TR25 survived.
    replaced TR25 with a 2SC945 moved the 2SC1312 over to TR26 spot (opposite the silkscreen this time!) and all is well with the world.
    LC
     
    #10 loosecannon, Mar 27, 2019
    Last edited: Mar 27, 2019
    NZ8N likes this.
  11. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    +1 to @loosecannon for sticking with it...

    (y)

    In light of your success - I just wanted to add that in comparing radio designs between two radios and others like the 640e - I've come across these little "tweaks" to make my life a little easier and the occasional radio operator that stumbles into our old shack looking for a rare part - often times gets special treatment because not of their good looks, just different news from someone new...

    So for those whom wanted to know why I even post this stuff, see the graphic of two comparisons above for reasons why radios like the PC-122 and TRC-465 work, but more could be done to improve their "sound" - not all are biased equally or for the best in response.

    Both amplifier designs use a critical value part, several actually, but I'll just list them off so you whom own one built like these shown above can try these on your own...

    R142 versus R148 - these two values tend to curve on their cutoff portions of the power curve that bias network uses for powering the outputs - if you can obtain one - try a 3K (simple 3,000 ohm) you've pretty much centered onto the working value you need.

    C115 and C108 - tonal filters - help out the AN612, but tends to make the AM Regulator seem to act "flat" in tonal response - these parts help keep the "shrill fingernails on Chalkboard" effects from ruining a SSB QSO - so if your careful - you can use lower values to obtain more fidelity as you see fit.

    R143, too bad the 810e could have used this too - but they compensated by balancing the 10X factor by keeping the 10X ratio for the 6.8K to 680 ohm impedance amplification issue. The same could be said about the input too - the 470 versus the 560 ohmic - these could be raised to the Mic's dynamic impedance and obtain a better distortion figure.

    In fact to help the user understand the "Distortion factors of Asymmetrical Amplification" - try changing the values of R146 100K or it's counterpart of R143 in the 810e - and use less like the 68K - for a good example of what I'm talking about - the clipping and skewing is far less and you have a really good sounding radio if you keep your ducks in a row. Remember the 10X - 680 - 6.8K to 68K factor. But then too - each one has limits - that includes the bandwidth. Go too far open in spectrum fidelity and the distortion returns - so watch out for the Capacitive values that tend to oversaturate the products, your output fidelity. Too much bandwidth and the parts are starving for more current to pass thru their junction. How well do you know your bypass - note the 220uF at only 6.3V or the 100uF at 10V - play with these values on lower scales (less uF) and you'll meet the Bandwidth limitations far easier than trying to open her up just to see what she can do.

    That seems to be the Crux of the many tailoring problems I face when it comes to maximizing the fidelity with what little you have to work with in the first place.

    I remember the older argument of "Why use something like that - when you can have this for $$$ more?"

    I guess that is what makes me a CB'er first - and a Radio Operator Second. I feel that it is more important to work with what little you have into making it better, than to buy more than what you will ever need - let alone use..."

    One of the aspects of my life - looking back to how I even began to understand radio - was to compare it to; how it came to owning and having to operate a car.

    You can buy the most expensive car just to get a towing package, but with a little ingenuity and some considerably less monetary investment - but more of your time invested in exchange for it - you can buy a lower cost car to work on, modify to meet the needs and have a vehicle that can haul your BUTT and Stuff around without having to leave a pile of crap sitting in the driveway from the other vehicle you had to buy. It is getting left behind because of the towing option on the vehicles was nice but all the extras took up way too much room, power and weight to be of any service or provision to use.

    Why buy the Leather Seats your careless friends Phart in, along with the DVD and WI-FI can only be used when NOT driving - if you're too busy getting from Point A to Point B?

    Same could be said for Hi-Fi; Injection versus the older Carburation (Venturi) principle...both work, one more for profile by torque and emissions but the other used the Vacuum and load to obtain similar results.

    Again ad Infinitum, Aspiration and Nauseam.
     
    #11 Handy Andy, Mar 28, 2019
    Last edited: Mar 28, 2019
  12. loosecannon

    loosecannon Sr. Member

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    Boy Andy when you're right you're right.

    trying to determine what is what when looking from radio to radio that are all "the same chassis" (yeah right LOL)

    it seems like they fired the engineer and asked the draftsman if he could do the engineer's job LOL.

    so many little differences, different part numbers, and slightly different values used, it makes one wonder if each particular radio got changed according to what the manufacturing house had lying around.


    thanks for the insight into the differences in the mic amps.

    here are the differences i notice between the 810e and the AX144 (not sure how this would relate to other versions, and i don't need to know yet LOL).

    AX-144 PRO-810e

    R142=3.3K R138=2.7K

    im going to try a 3K here per your advice.

    C115=330pF C108=.01uF

    In the ax144, C115 goes from base to collector of TR26.
    In the PRO-810e, C108 goes from base to emitter of TR26.
    (not really sure how to interpret this)

    R143=10 ohms R141=680 ohms to keep the amplification factor to 10x.

    R145=560 ohms R142=470 ohms

    not quite sure how much of an increase you were talking about here.
    did you mean that i should increase R145 to around 600 ohms?

    R146=100K R143=100K

    I am going to try lowering the value to say 82K first and see if i notice the difference, then i might try going down to 68K.


    thanks for all the tips.

    I still have to find the right part to remove in order to get rid of the channel muting while changing channels.

    I figure this out for all the radios i like to play with, just havent had the chance on this one yet.
    TR32 is not the way to go BTW.

    LC
     
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  13. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Look for a line from R107 - that heads off to Pin 15 "lock check" of the '24 and there is a branch that goes to the Channel Selector - I think you should look at it as a pull up scenario.

    The Channel selector runs a "detent" that operates a switch - once the knob is settled on a channel, the selector itself should have all the pins and wipers lined up internally to display channel and the proper BCD for the PLL to use - remember it does use a ROM to "check validity" of the input PINS for it's divisor. This switch is to enable the PLL to seek new programming and lock in to the new frequency - if it's not lined up the switch interrupts the PLL and inhibits operation until the Pin 15 "error" the switch is sending - is cleared.

    So scope or DVM the unbanded side of D26 (opposite side of Pin 15) and observe the "pulse" you get.

    You may find that the "pin 15" is the only way the PLL will even look for new programming - because it acts as if it needs a trigger to "refresh" the reading of the divisor pins - and checks against ROM for that validity else it' "halts" operation due to an "error".

    As these controls get old, that detent gets dirt and corrosion elements even in a sealed unit.

    PC-122 and 810e's are just as prone to this.
     
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  14. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    ... To Continue ...

    Now, I said the above to caution the rest of you that if the above strikes you as "Why didn't they do this in the first place" - let's take a closer look into the reason why "CB Radio" audio has such "distortion" - why did they do it like that?

    Bandwidth, and intelligibility - both are two factors that take Music end Entertainment into "Talk Radio" and "Shock - Jock DJ's".

    You lose "Paul Harvey" - but gain "Howard Stern" and "Rush Limbaugh" in the process.

    KEY_INTRO="Mission IMPOSSIBLE" TV Show theme...

    The Radio - if you decide to do this - will sound Ho-Humm and not reach a lot of users because it doesn't have the "bite" and pushing of the Envelope and its' bandwidth into the point of the intelligibility embedded in itself can be compromised due to a radio and FCC demanding such narrow filtering. You don't gain "punch" without the rapid rise and skewing, clipping and otherwise SMASHING the ceiling of the Carrier and bulging the Envelope into having to use all 440kHz of spectrum because the D*mn Dam burst...

    So - if any of your efforts are discovered, caught or demolished in the process - our Secretary will simply DELETE your Emails and refuse to return any calls made by you or your attempts.

    SEE=Hillary (SYN - Hilarity)

    This message isn't designed to destroy your endeavor to learn more. But, if you use this information to harm others...your radio might self-destruct - in less than 5-seconds.

    Good Day!
     
    #14 Handy Andy, Mar 28, 2019
    Last edited: Mar 28, 2019
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