1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Standby Circuit - Your opinion is needed

Discussion in 'Repairing Electronics' started by lynx, Jul 25, 2017.

  1. lynx

    lynx Member

    Joined:
    Mar 19, 2009
    Messages:
    221
    Likes:
    2
    Location:
    10km perimetrically
    Hi

    i need some guidelines for the repairing of an old home theater...
    probably some of you will say "why i bother and i don't get a new one"...

    i'm not fan of such devices but if i manage to repair it i will make a
    friend happy :)

    the model is Philips HTS3164, the VFD is not working neither the power led..
    there's no video output, thus looks like a dead unit.

    the power supply voltages seem fine .. 12V, 32V (for the amplifier), 5V, also manually
    ejecting the DVD tray it automatically closes when you connect the device to the
    mains...also some of the ICs on the main board they do power on becauce
    they get a little bit warm.

    i'm thinking the problem might be the standby circuit...in the following
    picture / schematic seems the standby is controlled by an MCU... P89LPC931
    (it's the fine pitch IC in the second picture over the connector)

    i need your help to diagnose if the problem is the standby circuit because
    i'm not that expert with such kind of repairings...but i'm able with a little
    bit help.

    thank you
     

    Attached Files:

    Last edited: Jul 28, 2017
  2. lynx

    lynx Member

    Joined:
    Mar 19, 2009
    Messages:
    221
    Likes:
    2
    Location:
    10km perimetrically
    any help?
     
  3. avionicsmaster1958

    avionicsmaster1958 New Member

    Joined:
    Nov 15, 2012
    Messages:
    4
    Likes:
    1
    Is there BK5V on the power supply board?
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. lynx

    lynx Member

    Joined:
    Mar 19, 2009
    Messages:
    221
    Likes:
    2
    Location:
    10km perimetrically

    Hi

    yes there is and it's 4.59V.

    also i've noticed that if i remove the red 7 pin connector seen in the photo
    on the previous post and then i connect the device to the mains, the
    power button led finally turns on but of course nothing else works.

    is this an indication that indeed the problem is in the main board?
     
    Last edited: Jul 28, 2017
  6. avionicsmaster1958

    avionicsmaster1958 New Member

    Joined:
    Nov 15, 2012
    Messages:
    4
    Likes:
    1
    There are two red connectors in the picture.

    4.59 seems a little low. Is that when it's connected to the rest of the system or disconnected?

    I think you have the service manual. Have you followed the TSS tree?
     
  7. lynx

    lynx Member

    Joined:
    Mar 19, 2009
    Messages:
    221
    Likes:
    2
    Location:
    10km perimetrically

    hi

    i'm referring to the 7pin red connector, if you remove it the power button led turns on
    4.59V everything connected, is low for the BK5V? what voltage i should expect?

    also the manual indicates i should check the standby circuit.
     
  8. lynx

    lynx Member

    Joined:
    Mar 19, 2009
    Messages:
    221
    Likes:
    2
    Location:
    10km perimetrically
    BK5V should be exactly 5 volts? not near that voltage??
     
    Last edited: Jul 29, 2017
  9. crutschow

    crutschow Well-Known Member Most Helpful Member

    Joined:
    Mar 14, 2008
    Messages:
    10,592
    Likes:
    477
    Location:
    L.A., USA Zulu -8
    ONLINE
    I had a dead VCR with low voltage on the 5V standby supply and, as I was poking around, nearly burned my finger on a hot electrolytic capacitor.
    It had gone bad and was leaking enough current to pull down the 5V.
    Replacing it restored the VCRs normal operation.
    You might check/replace all electrolytics to ground on the 5V.
     
  10. lynx

    lynx Member

    Joined:
    Mar 19, 2009
    Messages:
    221
    Likes:
    2
    Location:
    10km perimetrically
    hi, thank you for your reply, most capacitors already replaced but i will check again...

    i need a clarification, BK5V shouldn't be 4.59V? i think it's quite close to 5V with tolerance.
     
  11. lynx

    lynx Member

    Joined:
    Mar 19, 2009
    Messages:
    221
    Likes:
    2
    Location:
    10km perimetrically
    Finally repaired, for anyone else searching tips for similar units i suggest refitting the cables to exclude bad conduction issues.
     

Share This Page