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President AX44

Discussion in 'General CB Services Discussion' started by Smokinone, Oct 20, 2021.

  1. Smokinone

    Smokinone Well-Known Member

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    I'm working on a AX44. I can't find anything particular to this so I am using a Cobra 25 manual. I've replaced the electrolytic caps in this, and I checked everything in and out. Most caps were within tolerance, a few double the value, a few out of the game. 4.7 seemed to be the worst of the bunch for some reason.
    I've been going over the cap placement and pulled and checked a few just for curiosity's sake. All I have checked are good, no solder bridges, no components with bad connections
    I've no receive nor transmit...sometimes. Mostly not, but oddly, when I hold the radio at an angle it sometimes starts working. Receive and transmit. Well, it did for a while, but now I can't seem to duplicate that even. My x-tal is reading at 10.239, as close as you get for 10.240.
    Channel 1 has 16.270 and channel 40 has 16.710
    Also the PA works perfectly.

    Well, it started to work again, then quit. I don't know if it's under the mic connector, or some where on the mixer, pll side. It's just a hit or miss that it kicks in, and I can't duplicate it on a consistent level.

    Driving me knuts.



    Help? I'm running out of ideas.

    voltage(s) chart looks good as far as volt readings.
    ax44_voltage.jpg



    AX44.JPG AX44_2.JPG AX44_3.JPG AX44_5.JPG ax44-1.JPG
     

  2. NZ8N

    NZ8N Well-Known Member

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    Have you checked the ribbon cable from the Channel Selector to the main board? If the PLL does not "see" a valid 7 Segment Display code, it only takes 1 glitchy (intermittent) line to make the PLL shut down.
    I have one of these AX44's in my storage, I need to pull out my radios and go back over them sometime.

    From the PLL Data Book (Lou Franklin)

    PLL Data Book - TC9106 (Cobra25).jpg

    PLL Data Book - TC9106 (Cobra25) Pinout.jpg
     
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  3. Handy Andy

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

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    I concur with @NZ8N - if you needed a second opinion...:)

    One of the main things I see in this...

    This is similar to a Cobra radio - like a 25 - but this one got "baked" in a hot car, can tell by the wax wetting and scorching it took from the heat and cooling cycles the thing survived in.

    So that means - when you "tilted" the radio - there must have been loose - by hairline cracks - soldering or even the BCD channel selector needed work - note the soft riveted plastic - can deform. This can loosen the BCD switch's innards to a point they don't make the best contact - on top of the age of the radio the last setting is what it remembers the most during storage.

    upload_2021-10-20_7-56-58.png

    If you ever saw the BCD switch it's a miracle they even work, they are dual sided wafers one side with the programming for the PLL, the other side handles the LED display channel "digits" and there is a set of wipers, small arms or "tangs" that rub against the dual sided wafers - making contact. So one side is "hot" for channel, the other side is cold, for the PLL to ground specific pins for the ROM access - on top of, a separate "clear to go" signal switch that works on a detent that sends all the pins to GROUND for the proper ROM selector to even engage - so you can inadvertently mis-set the ROM encoding by setting those wafers on the rotary to mid-detent to try and skip channels.

    I've "oven baked" the BCD switch and using oven gloves worked the wafers to try to re-seat and reliquify the lube that these things used for their lifetime - so it will need TLC to recover this radio.
     
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  4. Smokinone

    Smokinone Well-Known Member

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    Without having a specific manual, it makes this a little more difficult. For instance TR15 has differing voltages depending on which voltage charts I have downloaded. It is also a 2sc380(0). I do have the 10.240 at the base of TR15 feeding pin 2 of the PLL.Pin 9 of the PLL has 16.710 on channel 40, and 16.270 on channel 1. I also get those frequencies at R6, one of the test points.

    All the readings on the PLL seem to be OK, they are changing voltages on the PLL for the channels. Wouldn't that indicate the PLL and the encoder/channel knob is working? Not questioning your knowledge, just mine. I'm trying to get an understanding of all this.

    It's almost like it stuck in between receive and transmit if that makes sense. Then, now and then it's golden and it all comes to life...but I can't do it twice consistently. And it seems also that I can be holding it a different way. It's like...haunted.

    I can flex the board, slightly, and nothing changes, touching the foil side of the board produces all kinds of weird noises, but doesn't drop into receive.

    It may have been in some kind of smokey environment that's for sure. Nothing looked burned or melted as far as aesthetics as far as case, knobs. The faceplate is unglued, so it probably was in a car as I have a radio or 2 that have done that. I cleaned a lot of black soot off on the inside of the radio.

    Just found my photofact 207 for the Cobra GTL. It's a little different that what I have collected. But, the PLL alignment initial readings are all good, except the transmit portion at the antenna feed.

    AX44-align.jpg
    I'll be trying to check some voltages to see where I lose whatever it is that needs to be turned on to get this operational. There should, I would think, be something missing somewhere that could point me to the area of concern...I hope.
    I haven't been able to get it to come back to life lately.

    Thanks for the input. I'm probably missing the point, but will re-solder the area.
     
  5. Smokinone

    Smokinone Well-Known Member

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    Did some cleaning of the board, top and bottom just to basically clarify what I was looking at. Re-flowed the areas mentioned. No changes. I actually pretty much re-flowed the complete board. No changes. I'll come back to it a little later and think about it.

    clean1_a.jpg clean2a.jpg
     
  6. Handy Andy

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

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    When you checked the PLL, this leads more into what you did to troubleshoot, so you're progressing fine...

    The Tilt problem then looks less of a loose connection or board assembly - but doesn't rule out bad soldering.

    There was a concern if the radio got "face planted" - dropped off a counter landed on one of the sides or a control - usually the channel knob - you'd know it by it binding or "lobbing" where it rotates more eccentrically than just a true plumb rotation.

    Doesn't sound like it now...

    Keep at it though...

    To me the "locks in then quits" tells me there's some issues around what I call Wax Creep , the wax you removed there's still more caught between components and the coil - so not only will it need a recapping - the intermittent problem could be just from the wax creep itself contaminating the parts
     
  7. Handy Andy

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

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    This is why I mention "wax creep" as well as bad soldering...

    Just two spots in a quick overview - I use Windows and "Magnifier" tool - to catch this...
    upload_2021-10-20_20-53-39.png
    It may be nothing but a shard off a ground pin next to a BCD programmnig pin raises an issue of reflow.
    The other one to the left deals with what is over by the coil (L15) and what you may have inside it...but the arrow points to a blip I would reflow to see if a lead didn't get covered well enough.
    • that (Gosh Darn) Wax that may have entered into the base of the can and now may have changed the resonant cap used to "tune" the coil to a range of tuning in MHz
      • - that cap looks like a tiny canister - might need to remove the can and clean it out.
    This is what I meant when a radio sits in a hot car and the wax then can melt and creep into
    and around and thru spaces changing the peaking frequencies.​
     
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  8. Handy Andy

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

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    Ok with this so far?

    You mentioned several times the radio works if given the "right conditions" - you'll need to closely observe the radio during this time for things like...

    S/RF meter - showing indication of any signal?
    • One of my favorite and simple go-to methods is to simply use an older CB radio on a dummy load using a portable power supply and set up that radio to throw a dead key - even with the mic engaged- to help you "listen" to this radios (your AX44) performance and operation under these conditions of receiving. Any empty channel so you don't annoy the locals will do... Sometimes the speaker of your test radio - is the one causing you not to hear anything because of something wrong with the speaker, the spyder cage it's cradled in, or the speaker wires are loose.
    CB/PA switch and Volume and SQ controls work like they should?
    • You hold it the "right way" it seems to work...
      • is the Front panel securely fastened?
      • Do switches seem to work - flipping - toggling them - introduce a lot of static or change the working condition?
      • How about the back panel?
    This is why I ask this...
    upload_2021-10-20_22-2-58.png
    The radio is certainly used, and has oxides and shows there was some hands back there...

    So was this radio a drivers "slip seater" one that he used to take in and out of a truck?
    OR in some vehicle or environment exposed to smoke or harsh fumes?​

    It's little things that help develop a picture of how a radio was used, can also give you insight into how much abuse or potential of other things that did go wrong that interrupted this radios life with it's owner?

    A bad speaker jack, a loose front panel switch (or well used one) or even bouncing inside on a dashboard with all the wires torqueing the case and chassis in different ways while the driver drove this with windows open ... I mean this thing was last made in the late 80's maybe early 90's - so whomever had this - used it for some time.

    Even the Mic Jack, and plug are suspect as being potentaitlly damaged - easier to abuse when in use - and especially prone to failure and easier to notice of anything to see - if the RF meter works to receive your dummy load carrier - but you don't hear it - means you've got more of a wiring problem than failed circuits...

    I see "heat" marks on a lot of the wire insulation in the point to point wire jumpers - so this radio got a good workout and you have some more work to clean up - so what to look for?

    You've seen the Wax - creep and other things, but also too - the slugs, the pots inside the radio and their condition and location of rotation when first found - also can tell how this radio fared in the hands of a previous owner...

    upload_2021-10-20_22-16-21.png

    I'm not putting you under Analysis, just using the radios pictured conditions of specific areas to help you determine what is your next move...The Yellow Box is IF gain - looks like it's turned up all the way so you know it isn't the BEST setting but someone did do something to this radio. The Purple Pulled Coil and the AMC (a.k.a. - MOD pot) cranked to off are other Strong clues.

    Various little things can make a radio "stop working" because of an adjusted coil or wrong pot turned - the components themselves are suspect too. You know there was a lot of "dirt" inside - so are those components affected have been exposed too - age and heat are two main killers - vibration finishes them off.
     
  9. Smokinone

    Smokinone Well-Known Member

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    I addressed those areas you pointed out, looked like some of the resin or shellac left over, I did re-flow and clean without any results. I pulled the L15 can out. I really didn't know what to look for but from the underside it looked clean I didn't want to try and pull the shield off the coil area, should I have? Anyway, when making adjustments, the L15 was able to adjust voltage to the 3.5 on 40 as stated in the alignment procedure.

    For some reason the radio started receiving again, briefly, didn't have time to check transmit but I'm sure it would be OK.
    As I was receiving and keying up with a nearby radio, I touched the large green poly cap next to the L15 can and it all dropped off, came back, then dropped again.. So, something around that area could be the issue. I am reading your helpful comments Andy, while doing all this testing, re-flow. I will pull some of the components around the L15, starting with the large poly cap C73 I think it is. It's a little crowded in there.
    So, you put me I think in the ball game here on the area of concern.
    Strange stuff going on here...
     
  10. Handy Andy

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

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    Oh geez!

    Those darn Green Mylar - polystyrene or Green Chiclets - are rearing their ugly head again...

    Sigh, then just replace them with a simple Disc cap of M or J tolerance - you should be ok.

    The "Mylar" in those things' packages or whatever - is much like a balloon for kids birthdays...
    upload_2021-10-22_9-48-35.png
    Ok, well, you don't have to get so "dirty" about it...
    :)
    Just the Mylar and the lead in the package leading (ahemn) to the Mylar inside is failing - just use a disc cap.

    Although Mylar is a good audio cap - the failure rates in mobile environments seems to be too high even for my liking - and yes, I have personal experience with those (Gosh Darn it!) things...
     
  11. Smokinone

    Smokinone Well-Known Member

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    I don't really know the history of the radio, it was in my late father-in-laws collection. The radio was working until the re-cap, after, it started acting goofy.

    I went and removed the poly cap in C73 and replaced it, checked the R60, good, and the D11. All good. Put em back in and still a no go as far as coming back to life. I also cleaned the area of the wax before replacing.

    These intermittent issues are a real pain.

    I gave the mentioned pots a little tweak back and forth, no changes there.

    The sr/f needs replacing as well. If we can get this back to operational I will get one from the multi star guy on the bay.
     
  12. Smokinone

    Smokinone Well-Known Member

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    Well, I put in a Panasonic film cap, really didn't do anything, in fact the poly was probably OK, it did check at slightly less capacitance that rated, but was within tolerence.

    I am however slightly, no extremely embarrassed as I have found the problem.
    Going over my capacitor replacements, I have found that C101,102, and 103 were @0.22uf. I don't know how I could have made the mistake of putting them in as they should be 2.2uf. Now that I have the correct capacitance, I'm up and running and made a local contact with good reports.

    I appreciate the helpfulness here, and this may serve as a reminder to me to do things in a more careful manner. For one, I usually change a few caps, then check. I didn't this time. I also should not only check, but recheck, and then check again what I'm pulling and putting back in. I always check the caps in and out, but something went amiss on these 3 particular caps. I don't do a wholesale pull either, I always pull one, check and replace. My capacitor box has only so much room so I have like the .22, 2.2, and 22uf pretty much in the same hold out in the box.

    So basically my inattention to details, brain fart, whatever we want to call it has come into play. The Cobra 25 has different values for these 3 caps as well, but I went through all the caps I had and identified what I had pulled, and what I had put in...didn't match. Evidently when I was poking around touching different parts of the radio, I added enough capacitance to kind of get it back on track, but it was short lived.

    I had started checking some of the caps to see if I had a bad one, but it was just bad values that caused the issue.

    Thanks Andy for putting me in the right area to probe, it brought me home..now to order a meter, and hope I don't make any more silly mistakes. Old eyes, old brain

    DSC02507.JPG
     
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  13. Handy Andy

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

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    That's ok, didn't mind working alongside to help guide you.

    Just understand that with experience comes a lot or rhetoric due to the nature of when someone says...

    "It don't work" - The Why takes a long time to wade thru. o_O

    Glad you have this thing working - and I'll bet the reasons for that intermitted lock was due to when you could sync it in, was from those moments the caps narrow range of tuning bandpass - allows the PLL to sense the VCO output - hence work against it's' own clock and function - if only for moments.

    It is not an easy catch but I'm glad you stuck with it and verified your work - SIGH - I've had my share of "total Losses" caused by being in a hurry or something else causing a distraction. So I'm glad you're able to recover this radio - not too many of them are left...

    This is a good thread - and I wish you well with your new addition to your radio family.

    All the Best!
     
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  14. Smokinone

    Smokinone Well-Known Member

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    I guess I was getting a little cocky...I've recapped 4-5 radios here as of late, so I got ahead of myself:cool:

    Thanks much:D
     
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  15. Smokinone

    Smokinone Well-Known Member

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    Just finished this AX44 up with a new SRF meter to replace the non-working one. Seems like it registers a little high, I may need to do a little more adjustment. When I get it at a lower reading, it doesn't quite show as high as it should when I have a strong signal, and when I adjust to the strong signal, it shows a high noise level. But at least it will be an indication that the radio is doing what it is supposed to.
    It adjusts OK on the power reading.
    newmeter.jpg
     

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