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Thread: National Panasonic SA-6200

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    Default National Panasonic SA-6200

    After many years I have fired up this unit. It works but sensitivity on FM seems to be well down and on AM all I get is noise.

    Anyone have a copy of the service manual that has a circuit schematic and alignment details?

    TIA.
    If Australia is a democracy why, then, is voting compulsory?

    "What has changed between the arrival of the First Fleet and today?"
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    Sounds like an antenna problem.
    another thing to try is earthing the chassis.

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    When I last used it the ferrite rod antenna worked well but a long wire really made it perform.

    I have never had to earth the unit ...
    If Australia is a democracy why, then, is voting compulsory?

    "What has changed between the arrival of the First Fleet and today?"
    "Wearing leg irons is now not required."

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    That's a nice 1973 vintage receiver you have there!
    Unfortunately I don't have a service manual for it in my repository.
    There are a couple on that e-pay site, but the prices are beyond realistic.

    Given:

    the age of the unit
    the fact it's been sitting for a long time
    your comment that when you last fired it up it worked well
    both FM and AM are not working as they should

    my suspicion is leaning towards electrolytic caps, and *possibly* resistors that have drifted over time.
    It's a long shot (but can't rule it out) that some of the transistors have started to degrade.
    I am seeing this a lot in vintage hi-fi equipment now - transistors especially from the 70s and early 80s which haven't failed completely but
    have degraded to the point where they don't function as transistors any more.

    Knowing the general layout of receivers of this age it will be all discrete components, I doubt if it will have any IC in it.
    The first place I'd start is in the power supply. Check all electrolytic caps for ESR and value.
    Then check all voltage rails.
    From there you'd need to address the FM and AM sections individually.
    It may turn out to be something common to both, but it's hard to give an educated guess without it being on the bench in front of me.

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    Keep in mind they werent very sensitive receivers in the first place , designed for citys where there was a huge signal , No comparison the today radios sensitivity by tenfold
    . Please treat people as you would like to be treated yourself.

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    Quote Originally Posted by Studio1 View Post
    my suspicion is leaning towards electrolytic caps,
    I am intending to recap the unit and take it from there. A schematic would make the task a lot easier though!

    Quote Originally Posted by hinekadon View Post
    Keep in mind they werent very sensitive receivers in the first place , designed for citys where there was a huge signal , No comparison the today radios sensitivity by tenfold
    Sorry, I disagree with you there.
    If Australia is a democracy why, then, is voting compulsory?

    "What has changed between the arrival of the First Fleet and today?"
    "Wearing leg irons is now not required."

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    Quote Originally Posted by Studio1 View Post


    It's a long shot (but can't rule it out) that some of the transistors have started to degrade.
    I am seeing this a lot in vintage hi-fi equipment now - transistors especially from the 70s and early 80s which haven't failed completely but
    have degraded to the point where they don't function as transistors any more.
    That is a very long shot and affecting the HF section highly unlikely.
    High current and the associated thermal stress would cause semiconductor degradation which is found in the power amp and power regulation.
    It could be as simple as a single zener diode that has degraded to a point that the supply voltage to the HF section has dropped below a workable value.
    Generally I would expect the HF supply to be 9-12V or more on these older appliances. 5V questionable, 3V not back then unless portable.

    Aged zeners can exhibit all kinds of strange behaviour and that would be the first place I would look before changing all the electro caps, although the filter cap parallel to the zener could have bad leakage and drop the supply too. If it comes from a much higher voltage you see the resistor that has got hot and left a stain over the years on the PCB and could have changed it's value.
    Last edited by Uncle Fester; 21-05-19 at 06:22 PM.
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    Quote Originally Posted by nomeat View Post
    That is a very long shot and affecting the HF section highly unlikely.
    Not as unlikely as you may think.
    I have just finished replacing almost every transistor in the AM, FM and SW sections of a portable all-band receiver from the early 80s.
    Pretty much every one of them was bad. Some were so degraded they had gains of less than 5, one of them measured a gain of 1.
    As I said I am seeing this a lot in vintage gear - amplifiers, tuners, cassette decks, receivers.
    Last week I had to replace half a dozen small signal transistors in a hi-fi tuner for similar reasons.
    There are some well known types of transistor that are more susceptible to this 'rot' than others and many of them appear in vintage equipment.
    Whilst it may not be the case with the SA-6200, it's worth bearing in mind.
    Last edited by Studio1; 01-06-19 at 12:16 AM.

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    I am an avid collector of portable AM receivers from the 1960's and they all work well after restoration that did not require transistor replacement.
    What you experience might have been a certain rare batch of transistors where the encapsulation was done poorly for whatever reason so that moisture/oxygen could do it's worst but hardly a general feature of old semiconductors, where thermal, current or voltage overload were not the cause.

    I got a box full of OC139 (originally from 1959) and they all read an average hfe of 40 (datasheet 20-85)

    Care to list these 'well known' types here?
    Last edited by Uncle Fester; 01-06-19 at 01:10 PM.
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    Quote Originally Posted by Uncle Fester View Post
    I am an avid collector of portable AM receivers from the 1960's and they all work well after restoration that did not require transistor replacement.
    What you experience might have been a certain rare batch of transistors where the encapsulation was done poorly for whatever reason so that moisture/oxygen could do it's worst but hardly a general feature of old semiconductors, where thermal, current or voltage overload were not the cause.

    I got a box full of OC139 (originally from 1959) and they all read an average hfe of 40 (datasheet 20-85)

    Care to list these 'well known' types here?
    Sure. 2SA725, 2SA726, 2SA798, 2SC458, 2SC1000, 2SC1312, 2SC1313 to name just a few.
    There are many other 'problematic' transistors.
    I'm not the only person who has encountered widespread issues with these (and other) silicon transistors.
    Read any of the Hi-fi forums and you'll find the same things being mentioned.
    I am seeing the same problems with quite a few silicon IC as well, and again it's not just me.
    A number of colleagues who are electronics technicians are reporting having the same issues and needing to replace many silicon devices from the 70s and 80s.

    Your germanium devices are likely to be fine.
    I don't see many electronic units with germanium devices in these days so I can't comment on their longevity or reliability but in general when I do find them, most seem to be Ok.

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