Harman Kardon HK 3490 Amplifier Completely Dead, No Standby

Discussion in 'General Electronics Chat' started by NTL1991, Jan 30, 2013.

  1. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    Hello,

    I've got a Harman Kardon HK 3490 Stereo Integrated Amplifier and it won't turn on. It's completely dead. With the unit plugged in and the main power switch on the back of the unit turned on, even the amber standby LED won't illuminate. No buzzing, humming or any clicking noises from relays. The main power switch tests good and mains voltage is getting to the board. From there I'm not sure... Both fuses in the unit test fine.

    Would the main power transformer be suspect? What feeds the amber/blue power LED on the front of the unit? I have the Service Manual for the unit attached.

    Any ideas where to look next?

    Thanks!
     
  2. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Start by checking the area on page 39 lower right.
    The small secondary transformer, more fuses, regulators etc.
     
  3. tindel

    Active Member

    Sep 16, 2012
    568
    193
    If nothing is happening then I'd guess that you lost the 5V standby voltage for some reason.

    I'd start by checking pin 3 on IC11 (s/b 5.6V). If 5.6V is present, then I'd check all the cables and make sure they are all fully engaged and/or don't have any problems (signs of excessive heat, bent connectors, frayed wires, etc). If 5V is present, let us know, and explain in detail what you found and there will be additional testing to perform.

    If 5.6V is not present, then I'd look at pin 1 on IC11 (s/b > 7.6V). If it is greater than 7.6V then I'd check the voltage at pin 2 (s/b ~0.6V). If pin 2 is anything other than 0.6V then IC11 or D108 needs replaced. If pin 1 is less than 7.6V then I'd check the output of T102... please be VERY careful double check that you are looking at the output pins and that you meter is in voltage mode (as opposed to current). You should expect an AC signal voltage higher than pin 1.

    Above all, please be careful - this card that you will be probing has lethal voltages (110 in the states, 220 abroad). If you're not comfortable doing this take it to someone that is.

    Really, my guess is that IC11, D108, or both are failed based on your description - or a bad connection somewhere.

    Usually if a transformer goes, you know it... lots of smoke, sparking, and a high possibility of fire. The intact fuses indicate that your transformers are okay too.
     
  4. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    Thanks for the lightning fast replies.

    I'll be sure the check the circuits mentioned. I'm glad the non-blown fuses are an indicator that the power transformer should be okay.

    I've done quite a bit of work recapping antique radios, but looking at the circuit diagrams for this modern amp had me a bit intimidated.

    I took the DSP, Video, and Tuner boards out to look for any obvious signs (dark areas on the main board, bulging caps, wiring issues), and then put everything back together so I wouldn't loose anything in the meantime.

    I'll pull the boards back out and start probing the main board tomorrow, posting my findings when I'm through.

    I really appreciate the help!

    Thanks,
    Nick
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Look for any bulging/tilted/odd looking electrolytic caps in the power supply section.
     
  6. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    OK. 0 Voltage at both the input and output pins of the 5V regulator (IC11). Input side of T102 has 117V (I'm in the US), secondary side has 0V.

    Nick
     
    Last edited: Jan 31, 2013
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Is there any voltage across the fuses on the secondary side? Sometimes they can look good, but be blown.

    If the transformer output is 0V with all secondary connectors disconnected from the PC Boards, then there is an issue with the transformer.

    Are the other voltages showing OK, is it just the 5V that doesn't have input?
     
  8. tindel

    Active Member

    Sep 16, 2012
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    With mains unplugged, I'd start by removing the output terminals from the transformer I'd check the resistance across C113 (red wire on the 'high side' and black on the grounded side to eliminate the diode.) If the resistance is low say less than 100ohms then it's probably the capacitor or diode has failed. I'd also check C114 and D112 in a similar manner. I'd also check C112. You're looking for a shorted cap.

    If you don't find a shorted cap, then I'd do what thatoneguy suggested, remove the output connections to the transformer and see if the transformer is still 0V. If it is 0V, it's the transformer.

    The good news is that you didn't see smoke, fire, etc from the transformer so it might be fixable if you're handy and can find the open circuit in the transformer.
     
    Last edited: Feb 1, 2013
  9. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    I pulled T102 and checked for resistance. I have 5.5ohms of resistance between pins 3 and 4, the secondary side, and an open between the primary side, pins 1 and 2.

    I got this receiver in a non-working state so I'm sure as to what it did before it went out. Not sure if it gave off any smoke, flames or anything of that nature.

    So it looks like the transformer is dead? It's labelled "CLT5J033ZU", "SKP0204 - A161" and "9K1 SK" as well as "SP935002TF". There are a few sources for it on the web. Does this sound like the problem?

    Thanks for all the continued support with this issue, I really appreciate it.

    Nick
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    You may want to test the other transformer for continuity as well. If you received it non-working, there's no telling what all led to the failure.

    Are there any dark brownish spots on the back of the PC Boards? If so, that is a sign of overheating.

    Also look for solder joints that don't look like the majority of others, indicating parts were replaced.

    I've been handed various things that don't work, but were worked on by somebody else, so it can be a huge mess. Sometimes it really is as simple as replacing the transformer or other part. Most of the time you'll need to track down what caused the transformer to fail, transformers are very robust relative to the rest of the circuit.
     
  11. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    There are no dark spots on any of the boards that I can see.

    The unit looked completely untouched, all the original cable ties were in place which had to be cut to get access to the main board. The original adhesive tape was in place on the ribbon connectors to the different cards, and none of the screw heads had any signs of removal. It seems this was just a unit that stopped working and they got rid of it.

    If it's not just a transformer defect, and something else was causing the failure, is it better that the open is on the primary side rather than on the secondary side. I'm guessing if the fault was on the secondary side, I'd have a LOT more things to check.

    Looks like I'll get two of the T102's just in case it's not just an easy replace and go.

    Thanks,
    Nick
     
    Last edited: Feb 1, 2013
  12. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Being that T102 is connected directly to the AC Line, it may very well be the primary just opened. If a short on the secondary caused it to open there would likely be a burned smell and some evidence of overload on the windings unless of course it's totally metal encased.

    EDIT: Here's at trick:
    After replacing the transformer, wire a 60-100w light bulb in series with the AC line (acts as a current limiter), then power up the unit. If all is well the lamp should go bright very briefly, then dim down. If there is a short on the secondary the lamp will stay bright. This doesn't work for all situations but is usually ok with amplifiers.
     
    Last edited: Feb 1, 2013
  13. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    Yes, no signs at all of any burnt material, smoke smell or otherwise. Even the board area under the transformer is as clean as could be. The plastic coverings on the windings are in good shape, not discolored or melted/disfigured.

    I'll let you guys know when I get the new transformer in.

    Thanks Again,
    Nick
     
  14. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If you are ordering a new transformer anyway, you could take the tape off this one (or un bend metal slightly) to see if it is something as simple as the solder joint between the winding and the input wire. I've lucked out more than once with that type of failure.

    Don't use brute force to open it up, just gently peel layers back until you see the windings and where the wires connect. If the windings aren't black, it is most likely a wire break, hopefully at the joint, which you can re-solder and re-assemble to see how it works.
     
  15. tindel

    Active Member

    Sep 16, 2012
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    I agree with thatoneguy. If it's just an open, you might just get lucky and save yourself some money and save the transformer from going to the landfill prematurely. You really don't have anything to lose.

    At the very least, go get 2 or 3 bucks for it at the scrap metal shop so it's recycled.
     
  16. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    Interesting thought. I *do* like investigating things like that. It's a tiny little thing, about a cubic inch in size.

    I did notice on the primary side, A tiny hair-thick wire connecting to one of the pins. The other pin for the primary side did not have this hair-thick wire anywhere in sight.

    Nick
     
  17. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    And TubeGuy, I built a dim-bulb tester a few months back, so I'll be sure to plug it into that before I give it full mains voltage after replacing that transformer. I ordered 2 just in case. Besides, my AVR235 also uses the same part...

    I'm thinking maybe a power surge or something of that nature was to blame for the defective transformer...?

    Nick
     
  18. tindel

    Active Member

    Sep 16, 2012
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    There's your open... now if you can just get some wire in there to fix it. ;)
     
  19. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    Hahaha! If I didn't have one ordered already (or if I couldn't find a source for one) you better believe I'd be all for trying to fix it. :)
     
  20. NTL1991

    Thread Starter New Member

    Jan 30, 2013
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    So I replaced the standby transformer, put the unit back together, and plugged her in. Flipped the master power switch and the lovely amber LED came alive on the power button. Ahh!

    Pressed the power button. It powered up with a nice click, the VFD lit up and it displayed the last audio mode selected. Then the VFD went blank and displayed "VOLTAGE PROTECT, CHECK DSP" and powered off.

    Of course, not knowing the history of this unit, I came to the conclusion that something else was wrong with the unit as well, not just this bad transformer.

    I glanced around inside and realized I forgot to connect one of the ribbon cables back to the DSP board. Plugged it in, and voila! Functioning perfectly!

    I want to thank you guys for all the help. This is one of my first successful repairs on such a modern piece of electronics. It's very satisfying, to say the least. It's been a learning experience too, navigating through those schematics.

    Thanks Again! You guys are the best!

    -Nick

    [​IMG]
     
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