1. You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
    Dismiss Notice

Uniden Washington no modulation

Discussion in 'General CB Services Discussion' started by Spec2079, Mar 24, 2019.

  1. OldTech03

    OldTech03 Sr. Member

    Joined:
    Dec 15, 2017
    Messages:
    524
    Likes Received:
    755

    I can give you some idea of possible issues but it's speculation, But it's base on 50 years of component level troubleshooting on this type of chassis.

    I usually say that it's not rocket science but it can seem that way.
    There is a transistor in the radio that is directly modulated by TA7222AP since you have receiver audio it's a given? that the Audio chip is good? anyway, the transistor I previously spoke of is generally fed directly by TA7222ap IC. It has been known to carry the numbers TR35 AND TR34 respectively if either one of these is bad it would or could cause no modulation on transmit. Problem is you are not seeing any SSB output as well so this circuit may or may not be an issue.
    First If I were training a new tech to troubleshoot this from the wiper of the mic gain control on through the path to C121 making sure you have audio along that path right up to R99 then checking TR32 for Collector > emitter short so forth and so-on etc. Oh I included a schematic of the Washington it may help.




    washington11.JPG

    Ok well if you send it in you should know that the few that know what they are doing will suggest you replace all the electrolytic caps which most would here would also suggest do you have to do that YES/NO it is possible that the radio could function fine for some time but the caps are all 35 years old. This can run anywhere from 60 to 100 depending on where you send it and what quality of Caps they use another $25 or 30$ for shipping and then if the Caps don't fix the issue Well it would be more most likely.

    Well, I got it started if I made any mistakes, misspellings, goof-ups etc please, by all means, somebody speak-up.



     

    Attached Files:


  2. Spec2079

    Spec2079 New Member

    Joined:
    Mar 24, 2019
    Messages:
    19
    Likes Received:
    4
    Thank you will check those transistors.
     
  3. Spec2079

    Spec2079 New Member

    Joined:
    Mar 24, 2019
    Messages:
    19
    Likes Received:
    4
    I found something strange I see odd transistors put in backwards and are labeled A628R3F I found about 6 of them.
     
  4. Robb

    Robb Yup

    Joined:
    Dec 18, 2008
    Messages:
    11,099
    Likes Received:
    2,798
    Some replacement transistors may have a reversed pinout.
    emitter-collector base -OR- base-collector-emitter for an NPN transistor
    No real surprise there . . .
     
  5. Spec2079

    Spec2079 New Member

    Joined:
    Mar 24, 2019
    Messages:
    19
    Likes Received:
    4
    Found couple more and found tr-11 c945 as well reversed , don't know if that is the issue
     
  6. Handy Andy

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

    Joined:
    Apr 23, 2018
    Messages:
    2,068
    Likes Received:
    1,869
    PartLeadPinout.jpg
    This is a sheet I grabbed a screenshot of in one service manual from that era - The radio is a Uniden but not exact, this radio uses the 945AQ amongst other SEMICONDUCTORS and Transistors that the chassis you have DOES USE. So this may provide some help in properly orienting the parts back onto the board.

    IT has been mentioned before, and I can't stress this enough. ...

    Since you got that radio from an unknown owner (you don't know the person that owned this radio before you and what they did to it) you are on your own when it comes to troubleshooting and any form of maintenance .You have to think of this as a start over, you'll have to recap, reflow and replace parts as you go - this is an old chassis and as said before AGE related issues like no modulation do come up with fixes that are some pretty wild places you'd never think would require a part replaced - again AGE and Owner related problems - else this radio usually would be a keeper for any good radio operator - they'd keep it - no need to sell it - sort of thing.
     
  7. OldTech03

    OldTech03 Sr. Member

    Joined:
    Dec 15, 2017
    Messages:
    524
    Likes Received:
    755
    Well, you must keep in mind according to what you have told us you only had an issue with modulation and TR11 would not be in the running for that issue. And all those other transistors most likely they are 2SA628's. I would say the issue is in the area that I pointed out in my previous post at the very minimum you need to eliminate that possibility. You need to know if any audio signal from the microphone is reaching C121 and then make sure it is passing through C121 and coming out the other side. Then you need to know if it is reaching R99 and passing through R99 and reaching C86 this is the kind of tracing that is easy to do with a scope and a good probe. Start at the wiper of the mike gain control set the scope to a sensitive enough level to see the audio produced by the mic at the wiper with the wiper full clockwise position. When you know that there is audio being found through the path laid out above it will let us all know what you may be dealing with or at least what you are not dealing with. Know you could jump right to C121 and R99 junction if you don't have an audio signal there then you could work backward or suspect TR32 has an Emitter/Collector short or even C192 could be shorted, is it probable C192 is shorted Maybe/Maybe not but if you do this tracing through the circuit with the scope you will maybe find the answer. In the old days, I and even now I use a simple signal tracer for things of this nature at least when training someone how to do this level of component testing. I love my new Rigol scope it's great so I use it most of the time. Anyway, you will never get a better feeling when you accomplish finding a problem using methods of this nature.

    I uploaded the schematic for Washington just look at the mic circuit like a water pipe pin one is hooked up to a water line and trace the flow from there as you would expect the water to flow. Now, this is very simplified but in this circuit, it works to look at that way.
     
    #22 OldTech03, Mar 25, 2019
    Last edited: Mar 25, 2019
  8. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    2,778
    Likes Received:
    2,563
    A reversed transistor is ALWAYS "a" problem. Might or might not be "the" problem.

    I don't ever remember seeing a type 2SC945 built with reversed pin assignment. I have seen several other types this way, but NEVER a 2SC945.

    That being said, this is sounding more and more like a sabotage radio.

    Not in the meaning of intentional sabotage.

    More than once a customer has brought in a radio that someone else had tried to fix, but failed to get it working. I tell the customer that for every time someone "tried" but failed to get the radio fixed, you should expect at least one or two new problems to be found in the radio. New problems in addition to the original fault.

    This is sabotage, just the non-intentional kind.

    By the time three folks try and fail to get the radio working, it may have a half-dozen or more separate things wrong inside the radio.

    The charitable way to describe this is "muddying the water".

    Leads me to the question, how many attempts have been made to fix this radio since it first broke down?

    Sure does sound like more than one.

    73
     
    Robb likes this.
  9. OldTech03

    OldTech03 Sr. Member

    Joined:
    Dec 15, 2017
    Messages:
    524
    Likes Received:
    755
    Nomad this response is meant for Spec2079's benefit but all that you have stated below I'm in complete agreement with.

    Also, the only numbers I could find for the
    2sA628R3F would be 2sa628 which is a PNP type and if Speck2079 could confirm that the transistors he is seeing like this are maybe TR7,14,31,45,30 these are where we would normally find 2SA733's in a radio of this vintage?

    And just for Spec2079's info, a 2SA is always a PNP type as Nomad will tell you as well so if TR7,14,31,45,30 if these are where you found them it's quite possible that Nomad's theory of someone messing around in there is correct as these may have been subbed for the original. Also the 628 and 733 appear to have the same lead configuration but again like Nomad I can't tell you the 628 was ever configured differently so ARE WE HAVING FUN YET?

    A reversed transistor is ALWAYS "a" problem. Might or might not be "the" problem.
    ==============================================================
    The above is certainly true that being said it was stated by Spec2079 the only problem was no modulation on AM and no SSB so it seems inconceivable to me that TR11 could be an issue unless he also has no receive.
    ==============================================================
    I don't ever remember seeing a type 2SC945 built with reversed pin assignment. I have seen several other types this way, but NEVER a 2SC945.
    ==============================================================
    Again the above in your world and mine goes without saying never seen a 945 in any configuration other than the one we all know and love.
    ==============================================================
    That being said, this is sounding more and more like a sabotage radio.

    Not in the meaning of intentional sabotage.

    More than once a customer has brought in a radio that someone else had tried to fix, but failed to get it working. I tell the customer that for every time someone "tried" but failed to get the radio fixed, you should expect at least one or two new problems to be found in the radio. New problems in addition to the original fault.
    ==============================================================
    Again you are correct we have both had customers walk in with "I had Joe take a look at it but he couldn't find the problem" and this could very well be one of those. But again Spec2079 stated that the only issue he had was no modulation while having good receive and I assume all else was working.
    ==============================================================
    This is sabotage, just the non-intentional kind.

    By the time three folks try and fail to get the radio working, it may have a half-dozen or more separate things wrong inside the radio.
    ==============================================================
    The charitable way to describe this is "muddying the water".
    More like water skiing in muddy water with boulders just inches below the surface LOL

    ==============================================================
    Leads me to the question, how many attempts have been made to fix this radio since it first broke down?

    Sure does sound like more than one.

    Ok, Nomad please chime in as I respect your knowledge and as I said this response was for 2079's benefit and if I'm wrong about what I understand he as well should correct me. This is as much for my sake as anything trying to keep an Old mans failing memory relevant.
     
  10. Spec2079

    Spec2079 New Member

    Joined:
    Mar 24, 2019
    Messages:
    19
    Likes Received:
    4
    I'm taking it in for repair as I'm confused.
     
  11. Spec2079

    Spec2079 New Member

    Joined:
    Mar 24, 2019
    Messages:
    19
    Likes Received:
    4
    Thanks guys I sent it in for repair I didn't want to screw it up
     
  12. OldTech03

    OldTech03 Sr. Member

    Joined:
    Dec 15, 2017
    Messages:
    524
    Likes Received:
    755
    Where did you send it? And Happy birthday we both share April 20th
     
  13. Spec2079

    Spec2079 New Member

    Joined:
    Mar 24, 2019
    Messages:
    19
    Likes Received:
    4
    Mikes radio repair he has done other radios for me.
     
    NZ8N and loosecannon like this.
  14. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    2,778
    Likes Received:
    2,563
    Mike will get to the bottom of it, no doubt.

    73
     
    357magnum and NZ8N like this.
  15. OldTech03

    OldTech03 Sr. Member

    Joined:
    Dec 15, 2017
    Messages:
    524
    Likes Received:
    755
    Yes, I will be waiting for the video always like to know what the end result is. I'm Kinda having withdrawal symptoms not having my shop/bench setup but I will soon have it again.
     
    357magnum, Spec2079 and NZ8N like this.

Share This Page

  • About Us

    The WorldwideDX Radio Forum was originally established in 2001. We pride ourselves on welcoming Radio Hobby enthusiasts of all types, while offering unbiased, informative, and friendly discussion among the members. We are working every day to make sure our community is the best Radio Hobbyist's site.
  • Like us on Facebook

  • Premium VIP Member

    The management works very hard to make sure the community is running the best software, best designs, and all the other bells and whistles. Care to buy us a beer? We'd really appreciate it!

    Donate to us!