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Faint display on Aiwa Tuner

Discussion in 'Troubleshooting and Repair' started by Roadtoad, Dec 7, 2015.

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  1. Roadtoad

    Roadtoad

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    Dec 7, 2015
    I have an old Aiwa separates stereo system. The display on the tuner has always been dimmer than the other separates. Recently it became so dim that I couldn't make out anything at all. I have taken the cover off and checked for dry joints and cleaned the contact pins on the board connectors. The display has got a little brighter so that I can at least read it but compared to the other displays its still dim ( see photos) I downloaded a service manual but Im still unsure as to what to do next if there is anything that can be done. The service manual can be found here http://elektrotanya.com/aiwa_z-d9300m_mx-z9300m,fx-wz9300,tx-z9300,ge-z9300.pdf/download.html
    Page 67 shows an adjustment page and from what I can make out SFR1 is for the brightness but I have tried turning it slightly while the display is lit but it has no effect. Any suggestions ?
     

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  2. GPG

    GPG

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    Sep 18, 2015
    Nothing helpful on p67 Check C915, 916, p49 and -30V WH805. SFR1 seems to be for signal strength meter adjust p49
     
    Last edited: Dec 7, 2015
  3. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Which IC is driving the dimming Display? Could be faulty or the LEDS were over driven and they gradually faded
     
  4. shrtrnd

    shrtrnd

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    ARE, those LED's?
    It kind of looks like it might be one of the old flourescent vacuum displays, and they just get dimmer as they age (and nearly impossible to find a replacement)
    (And no, I didn't look at the manual, just the pictures, ... )
     
  5. Roadtoad

    Roadtoad

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    Dec 7, 2015
    To be honest Im not 100% sure if they are LEDs the thing is its quite an old system knocking on for 20 years old. As you say if it is the vacuum filament type they do wear out but....the tuner has always been dimmer than the other displays so if anything were to wear out it would be the brighter ones nes pas ? Also Im sure Ive read something about boosting the display with a higher voltage but I have no idea how to go about this. I have three options 1. Look out for another tuner on the second hand market. 2. Live with it. 3. Fix it. Option 3 is my choice as I am retired now and have the time to mess about with it and although this may sound strange I have got attached to the thing. They dont make them any more indeed Aiwa although an excellent make went bust not through quality issues but because they didnt plan ahead into the digital era. Also Im a nutter
     
    Martaine2005 likes this.
  6. Martaine2005

    Martaine2005

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    May 12, 2015
    The FL901 is a filament heated display to Pins 1,2 and 34,35.
    Check voltages and the capacitors as GPG suggested.
    I would go further and check all the capacitors.
    In you middle picture, bottom cap looks swollen. Or is it camera angle? C80 I think.
    You could try reflow the solder to all the pins of the display in case there are cold joints.
     
    Last edited: Dec 7, 2015
  7. Roadtoad

    Roadtoad

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    Dec 7, 2015
    Thanks GPG + M2005, I have an ammeter, excuse my ignorance but what level voltages should I be looking for ? How do I test a capacitor ?
     
  8. shrtrnd

    shrtrnd

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    Jan 15, 2010
    The fluorescent displays operate at a pretty high voltage. (So be careful and see if it's listed in the manual) And again, they DO wear out with age.
    There probably is a pot in there to adjust the voltage for the display (within a small voltage span range).
    If you've tried it, it may already be set at it's maximum.
     
  9. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Ahh, my bad .. simply saw the led like segments
     
  10. GPG

    GPG

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    Sep 18, 2015
    The manual you directed to, the index says 86p but only 67 are available. What model No. The VFL display whatever the model will have the filaments/cathode connected to the two pins at each end of the displays line of pins. the usual voltage is ~3Vac check for this. In the diagram I loaded, the ac voltage is coupled to the display through 2 electrolytic caps Trace and check the voltages. The -30 V is also for the display
    I'm not a believer of the shotgun approach til I establish cause
     
  11. Roadtoad

    Roadtoad

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    Dec 7, 2015
    Hi GPG,
    Its the TX-9300YEZ. The manual does indeed show 67 pages but if you scroll all the way through there are 85 pages I dont know why this is. The whole document shows it to be for the complete system the D-9300M. The tuner is just a part of the whole system. As I said before the brightness of the tuner display has always been dim but I dont think it will be wear related as the brightness of the amplifier for example has not lost any of its glow. Bear in mind, the amp is always on whatever Separate I may be using with it. There is a tape deck, cd, turntable, graphic equalizer. With the exception of the turntable which has no graphics the other items are not always on thus the graphics of the amp get by far most use. Incidentally This system when new in the mid 90s was around the £1000 mark. I only paid half this however as it was for sale in a catalogue returns shop in Bradford where I lived at the time. I could never find anything wrong with the system other than the graphics of the tuner being on the dim side. Thanks for your help BTW
     
  12. Martaine2005

    Martaine2005

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    May 12, 2015
    Hi Roadtoad,
    Apart from the obvious caps and voltage as GPG suggests, check the displays pins solder joints too. A cold solder joint will give similar symptoms. Some of the display is visible while other sections are very dim. Which is why some members thought it might be LED.

    If I were you, I would check the voltages on the amp displays four outside pins as they are very likely the same.
    I can't read the schematic properly without printing it! I keep losing myself.
    There is no shotgun approach by replacing all caps in a twenty year old audio separate!. The caps that are good have already out lasted their general lifespan.
    Also checking the displays pins for dry/cold joints is a valid point, as the unit had this fault from new..

    Martin
     
  13. GPG

    GPG

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    Sep 18, 2015
    As far as I can make out (without printing and taping) there are two sources for the filament supply for different units. One is from the Mains transformer and the other from a converter. This is one of the reasons I used to advise against these type of systems, they are not truly separates. The page No's for measurements/components I noted are Adobe PDF not the ones on the document. Do not adjust anything on spec. The control you adjusted sets the "tuned" threshold and without the test gear is not able to be accurately reset.
     
  14. Roadtoad

    Roadtoad

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    Dec 7, 2015
    Thanks folks, So Ive checked all the pins and all look to be ok. On document 65 I can make out the main voltage supply to the VFD as being C915 and C916 which go through F1 and F2 and switched through the controller IC901. Should I now test the voltage at F1 and F2. I am a complete novice at this so Im not sure where to place the probes of my multimeter or what voltage I should expect. Im sure this is just an isolated display problem on the tuner as the sound is perfect and all other functions seem to work fine
     

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  15. GPG

    GPG

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    What meter do you have?
    Doc 65-66 Measure voltage at display pins F1 to F2 AC voltage. Measure between F1 ,F2 on con 2 AC
     
  16. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Toadroad . . . . . .

    Whoooops! my dyslexia kicking again . . . . amend that to Roadtoad

    Submitted herewith are snippets from the schematics of the 3 principal display units of your magnificent system, with its GRAPHICS EQUALIZER display utilizing totally different display technology.

    The CASSETTE display electronics uses a 12V supply passing thru Q152 voltage regulator to feed power to cross coupled Q901-Q902 F/F transistors into T901 to provide -22VDC and 1.6 (or) 3.2 VAC to
    the filament of the display unit.

    The display of the MAIN AMP unit initially has 6VAC coming out of P(ower) T(ransformer) 2 that then passes down the RED DOTTED PATH until one leg feeds into the Q95-96 pair of switching transistors,
    utilizing tandem NPN and PNP transistors to alternatively pass both polarities of the 6VAC. . . . . IF . . . . . a common base turn voltage is coming in to them from Q74.
    The initial AC voltage, now being switched and reduced (by the Q95-96 semi junctions) then passes on down the RED DOTTED PATH to the end 1+2 and 34+35 filament string connections of the FL901
    display unit.

    Now here's your one of importance . . . . . its TUNER unit display :

    The very same 6VAC supply voltage that fed the MAIN AMP display is also being routed from the power amp, out its FC801 connector to the tuners CON2/PIN902 connectors.
    The pins 6 and 7 of connector PIN902 exit as F1 and F2 lines passing down the GREEN DOTTED PATH and immediately encounter C915 and C916 in line and are each presenting a 8 ohm impedance at AC line voltage frequency of 60~.

    A voltage dropping occurs and the GREEN DOTTED PATH of the filament supply line continues direct to the pins 1+2 and 34+35 of the string filament within the FL901 display.
    ( Remember . . . . . on the like circuit of the MAIN AMP display unit, a voltage drop was incurred by the switching transistors junctions, on this tuner supply they opted to use cool running electrolytics
    instead of dropping resistors )
    BUT . . . . .with onset of time, that seems to have proven to be a fallacy.

    Now what to do . . . . . . what to do . . . .either just jump in there and change out the two 330 ufd units.

    OR . . . to fully satisfy your curiosity . . . pull the cover to get access to the same family display in the MAIN AMP unit and read the AC voltage across the end pins of that display, and then compare it
    to the present AC voltage that is being found on the filament pins of the TUNER display unit .

    On both units there is being a -22 VDC supply involved with all the "Plates-Anodes" of the switched display segments, but I do not suspect it at all, just a reduced filament string voltage, due to progressive
    loss in capacitive values of C915-916.

    Take particular note in the treatment of the POLARITIES of the capacitors involved, when being used to pass AC voltage through them.

    Thasssit . . . . . .


    Its in the book . . . . . and here's da' book :

    (Clickee-clickee . . .to makee mo' biggee )


    [​IMG]


    73's de Edd


    .
     
    dorke and Tha fios agaibh like this.
  17. Roadtoad

    Roadtoad

    13
    1
    Dec 7, 2015
    Thank You 73's de Edd for that comprehensive breakdown of the possible problem and for the compliment of my system which I think deserves to be repaired. Im not sure about how to test the two caps but I have confidence in your diagnosis and I will just swap them out. See pics. Should keep me busy for a while.I also show my cheap multimeter which I dont know is up to the task 003.jpg
     

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  18. GPG

    GPG

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    Sep 18, 2015
    Use the meter 200V~ (white) setting, If you can borrow one with a lower range would be better. 200V= for the -30V .
     
    Last edited: Dec 16, 2015
  19. Roadtoad

    Roadtoad

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    Dec 7, 2015
    I cant find the exact spec (330uf 16v)capacitors for sale so could somebody tell me if I can change the spec I can only see 330 uf with either 6.3v or 25v ?? Thanks
     
  20. 73's de Edd

    73's de Edd

    3,068
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    Aug 21, 2015
    Sir Roadtoad . . . . .

    Perfectly fine to upgrade up to the 330 uf at 25v, with its greater voltage specifications safety cushion.

    Pee Ess . . . . .
    That meter looks just fine to me, with its available ranges, and particularly, its separate high current reading capability.

    BTW . . . . .since you showed its pic.
    I placed yellow highlighting on all but one of the central filament strings that transverse the display unit.
    With our suspicions being, that the temperature for optimal electron emissivity, to cross over to the displays plates/anodes is currently being a bit deficient,
    [ Probably due to a slightly lowered supply voltage being supplied to it (the displays filament string) .]

    Le MARK UP:
    [​IMG]


    73's de Edd
     
    Last edited: Dec 16, 2015
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