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Thread: Kenwood AVS Receiver KRF-V5300D in protect blinking LED

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    Default Kenwood AVS Receiver KRF-V5300D in protect blinking LED

    Kenwood AVS Receiver KRF-5300D in protect with blinking LED. Would apply to other models like KRF-V5200D etc.

    Unit would briefly power up and go protect, Standby LED rapid blinks.

    Found both AVR & IC-PROT2 , & AMP DC-PROT1 active high

    Checked -12V (7912 reg IC4) & +12v (7812 reg, IC3) missing voltage

    Checked input side of both regs, missing -22.7V & +22.3V

    Checked Transformer output at CN2 pin 1 12VAC & pin 3 -12VAC, both present

    identified R527 , 528 1 ohm 0.25w flameproof resistors , discoloured, burnt , open cct.

    Replaced resistors, At this point the receiver was effectively fixed but remained with the same fault symptoms. So this was my dumb moment I'll share.

    voltages were restored but not in spec and unstable.
    +12V was erratic and 11.2-11.5v
    -12V was about -6V, replaced that 7912 and -12V but I'll get back to this.

    unit still failed.

    looking at the cct where the two protection circuits are, there was a checkpoint at zener cathode D305 3.3V and c303 + of 3.6v.
    I had 10V and suspected bad zener, purchased a replacement but diode check indicated it was ok but swapped out anyway - no change

    then proceeded to check all voltages and for anything shorted or open etc, could not find anything obvious

    If connector cn601 is removed the unit will powerup since the protect signals are now isolated. Risky move but i could not find any shorted items especially the amp modules.
    Nothing bad happened so connected cn601, earthed the protects and turned on, nothing bad, no smoke, hooked a speaker up and amp could be heard coming online through the speaker.

    So I'm back at the 10V which should be 3.6 or less I suspect. If 10V is on the zener reversed it should be conducting and pulling that down

    I've already checked that zener and swapped an axial 1/2w 3.3v so i'd run out of ideas. I thought I'd try it again but this time earthed to chassis and then on the + side on the cap. Voltage went from 10v to 2.5v

    I think some of you know where this is heading.

    Where did I go wrong? Nothing earthed correctly, floating gnds!

    None of these boards earth with the mounting screws but via earth brackets screwed to the rear panel. none of these were bolted as i had removed all these.

    Yeah, 2 nights poking and pondering the schematic with a dead end.

    So what about the 7912 reg coming good, well i'm pretty sure I used the chassis gnd for the low reading and after replacement used the actual gnd at the reg so original was most likely good.

    have not gone back to the original as I could not be stuffed now but once I realised what was going on, bolted all earth points up and working.

    So short version, missing +- 12V rails , open cct resistors cut AC before the rectifiers.

    I used the KRF-V5200d service manual as the boards are virtually the same, definitely the power board was.


    Edit
    Extra info.

    discovered this was after lightning which I forgot about. been sitting around for months, did a little work ages ago so explains both resistors blowing together. that's my theory on it
    Last edited by tw2005; 22-05-15 at 02:48 PM. Reason: lightning

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    I think we've all done that once or twice (or more)

    IE spend time chasing a fault we've introduced while tracking down the real problem but as long as there's a happy ending all's good.

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    Nice story. Well done on the fix.

    I scrolled slowly while pondering your tale and concluded that you had no ground return. In the past I've fixed a few AVRs with similar genuine faults due to poor grounding caused by rear chassis screws not making contact.
    Symptoms have ranged from annoying low level hum to no audio output. Took a long time to find the first time but it is one thing I check on all amps / AVRs. I fit star washers to make sure the repair doesn't bounce.

    As far as self induced fault go, I went through a stage where I would remove faulty parts, get distracted and then proceed to fit the same faulty parts back in the product! Many hours of fruitless activity followed until my stupidity was realised.
    This has led me to marking all parts I remove with a paint pen to protect me from my own foolishness. I also fully reassemble any repair that is going to be attended to at a later date. Lessons learned the hard way tend to be remembered.
    "The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom." - Issac Asimov

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    Default same problem

    Quote Originally Posted by tw2005 View Post
    Kenwood AVS Receiver KRF-5300D in protect with blinking LED. Would apply to other models like KRF-V5200D etc.

    Unit would briefly power up and go protect, Standby LED rapid blinks.

    Found both AVR & IC-PROT2 , & AMP DC-PROT1 active high

    Checked -12V (7912 reg IC4) & +12v (7812 reg, IC3) missing voltage

    Checked input side of both regs, missing -22.7V & +22.3V

    Checked Transformer output at CN2 pin 1 12VAC & pin 3 -12VAC, both present

    identified R527 , 528 1 ohm 0.25w flameproof resistors , discoloured, burnt , open cct.

    Replaced resistors, At this point the receiver was effectively fixed but remained with the same fault symptoms. So this was my dumb moment I'll share.

    voltages were restored but not in spec and unstable.
    +12V was erratic and 11.2-11.5v
    -12V was about -6V, replaced that 7912 and -12V but I'll get back to this.

    unit still failed.

    looking at the cct where the two protection circuits are, there was a checkpoint at zener cathode D305 3.3V and c303 + of 3.6v.
    I had 10V and suspected bad zener, purchased a replacement but diode check indicated it was ok but swapped out anyway - no change

    then proceeded to check all voltages and for anything shorted or open etc, could not find anything obvious

    If connector cn601 is removed the unit will powerup since the protect signals are now isolated. Risky move but i could not find any shorted items especially the amp modules.
    Nothing bad happened so connected cn601, earthed the protects and turned on, nothing bad, no smoke, hooked a speaker up and amp could be heard coming online through the speaker.

    So I'm back at the 10V which should be 3.6 or less I suspect. If 10V is on the zener reversed it should be conducting and pulling that down

    I've already checked that zener and swapped an axial 1/2w 3.3v so i'd run out of ideas. I thought I'd try it again but this time earthed to chassis and then on the + side on the cap. Voltage went from 10v to 2.5v

    I think some of you know where this is heading.

    Where did I go wrong? Nothing earthed correctly, floating gnds!

    None of these boards earth with the mounting screws but via earth brackets screwed to the rear panel. none of these were bolted as i had removed all these.

    Yeah, 2 nights poking and pondering the schematic with a dead end.

    So what about the 7912 reg coming good, well i'm pretty sure I used the chassis gnd for the low reading and after replacement used the actual gnd at the reg so original was most likely good.

    have not gone back to the original as I could not be stuffed now but once I realised what was going on, bolted all earth points up and working.

    So short version, missing +- 12V rails , open cct resistors cut AC before the rectifiers.

    I used the KRF-V5200d service manual as the boards are virtually the same, definitely the power board was.


    Edit
    Extra info.

    discovered this was after lightning which I forgot about. been sitting around for months, did a little work ages ago so explains both resistors blowing together. that's my theory on it
    hi, I need help, I have the same problem with my krf5200 d, I have followed all his procedures but I can not solve. You could specify the repair procedure, I'm not an expert, and my English is not perfect, so I have difficulties.
    thanks in advance Giovanni.
    ps. excuse me if I have broken any forum rules.

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