Connect with us

Backlight Screen problem AIWA 999

Discussion in 'Troubleshooting and Repair' started by nangeo, Jun 26, 2016.

Scroll to continue with content
  1. nangeo

    nangeo

    2
    0
    Jun 26, 2016
    I have an AIWA 999 stereo HIFI.
    The backlight of the screen doen't light. So i can not resd the digits.
    Only when i come very close to the screen i barely see something of the digits (frequency )
    What i can do ?
     
  2. 73's de Edd

    73's de Edd

    2,773
    1,159
    Aug 21, 2015
    .

    Sir nangeo . . . . . . .

    A cursory examination reveals that your illumination failure is not going to be a "burnt out lite bub" from a backlight illumination source.
    BECAUSE your unit is using a VFD . . . .Vacuum Fluorescent Display unit.

    Referring to the attached informative schematic snippets from that unit reveals:

    That unit needs an AC filament supply of ~4.9VAC, which is being derived from a dedicated winding on the main power supply transformer.

    ALSO there is a negative supply voltage being required for the display unit.
    It is initially derived as a 84VAC supply from the main power transformer and rectified and then processed and its
    regulation is being derived from Q102 and Q112 and it then comes out as a regulated minus 24 volts DC.

    All of this info and signal flow can be derived from parts A and B of the snippets.

    The REAL helpful info is from C where it gives the connections present on CON602.

    Find that CON602 connector on the unit and make an AC measurement across pins 7 and 8 to see if you have that ~5 being there.

    Then move down and use pin 3 for DC ground referencing and measure up to pin 5 to see if that required ~ 24 VDC is being there.

    About time for you to now seek and find.

    Relevant Schema / Snippet References:

    [​IMG]

    73's de Edd




    .
     
    Azlan and nangeo like this.
  3. nangeo

    nangeo

    2
    0
    Jun 26, 2016
    I want to thank you very much for your very fast response.
    i am not a technician of electronics but i will try to follow your instructions.
    i understand that i must:
    find CON602 connector on the unit and make an AC measurement across pins 7 and 8 to see if i have ~5 being there.

    Then to use pin 3 for DC ground and measure up to pin 5 to see if that required ~ 24 VDC being there.

    i thought , i had to change only some bulbs and thats all. lol

    thank you , anyway
     
  4. 73's de Edd

    73's de Edd

    2,773
    1,159
    Aug 21, 2015
    I was also hoping that your problem would just be a lamp (s) replacement, but after fully researching your unit, a more sophisticated display was found.
    I just have a feeling that the problem is not to be with the lower AC used for the filaments of the display, but with that minus 24 volts DC that the. display also requires.
    If so, we can then track it down, using the referencing shown on part B of the info that I supplied to you.


    73's de Edd


    .
     
    nangeo likes this.
  5. Azlan

    Azlan

    1
    0
    Jan 29, 2020
    Sir,i m also got same problem of my hifi unit.i ve try to use your circuit that you attach but found no match with mind.could you help me on this.my set was aiwa Z 1800.thanks
     
  6. 73's de Edd

    73's de Edd

    2,773
    1,159
    Aug 21, 2015
    Sir Azlan . . . .

    On my original plotted schematic for the 999, the unit concept is the SAME as yours in the power supply ( the right half of schema)
    You just need more relevant info on the left sides YELLOW marked up VFD panel portion . . . . .s o o o o o . . . . .

    Here is a custom UNITIZED schema of the Aiwa Z1800, of ONLY the relevant circuitry of one otherwise, somewhat co-MMMMM-plex schematic of your unit.
    The very top portion is being relevant to the visual display unit as the RED flagged unit and some relevant injection of the minus 30 volt VFL supply voltage .
    In addition, the display units extreme ends . . . of pins 1-2 and 48-49, are receiving a constant AC voltage of ~ 5.5VAC from terminals 11 and 17 of one of the PT1 power transformer windings.
    GREEN arrows are the power flow for the panels filament strings.
    BLUE arrows are the VFL negative 30 DC volts supply for the display.
    The -30 starts on the PT1 with a secondary of a power audio supply winding . . .with Term 14 ground and Term 16 supplying ~28 raw AC via the PURPLE arrow path to get voltage doubled with D106 and D107 . . .filtered with C106-107-108.-109 E-caps.
    Then Q102-Q112 along with Zener D114, regulates the now DC supply, on down to -30VDC and exits as VFL supply via the BLUE arrow path.
    This relevant schematic portion is also being BLUE flagged with its support / construction components..
    In the upper schematic portion, there is another, likewise, BLUE flagged area with its support components.

    Sooooooooooo . . . it now just looks like you need to place meter probe ground on CONNECTOR 601 or 101 pin #21 and power up the unit and probe pin 20 to see if you have the NEGATIVE -VFL voltage . If not, research at its point of origin back in the power transformer area.
    Then, switch metering to AC mode and check between pins 15 and 16 of CONNECTOR 601 or 101 to see if you have the filament voltage for the display. Finally lift either the 1-2 or 48-49 wiring end to disconnect the AC filament supply line, and test across the filaments to confirm flament continuity..
    Or in a TOTALLY dark area you might be able to see the frontally spaced out filament strings light up, HOWEVER, they do run at a VERY, very dim orange.

    AIWA Z1800 . . . . . UNITIZED SCHEMATIC SNIPPET . . . .

    [​IMG]

    https://i.postimg.cc/Zbyr69hq/AIWA.png


    Thaaaaaaaasit . . . .

    73's de Edd . . . .

    Having . . . Fun . . . Fun . . . FUN ! . . . at work . . . . .
    Put decaf in the coffee maker for 3 weeks.
    Then, once everyone has unbeknowingly and gradually gotten over their caffeine addictions,
    Switch to espresso !

    then . . . . its . . .


    https://i.giphy.com/media/j2MdMFNumkFeAAxfch/200.webp



    .
     
    Last edited: Jan 30, 2020
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-