+ Post New Thread
Results 1 to 8 of 8
  1. #1
    Newbie level 3
    Points: 30, Level: 1

    Join Date
    Jan 2020
    Posts
    4
    Helped
    0 / 0
    Points
    30
    Level
    1

    HKTS 220 Power Supply board troubleshooting

    Hi everyone

    I was hoping that someone would be able to help me out with my HKTS subwoofer power board. Having disconnected it for christmas, i was reconfiguring the setup and noticed it wasnt working so I decided to open it up and found some issues on the power supply side. I should mention that my electronic knowledge is rather novice but I am eager to educate myself in order to fix it yet at the current moment my limits have been reached.

    Initially I discovered a rather darkened resistor (R23) and decided to swap it for a new for good measure. The old did however test out and was within tolerance.
    Click image for larger version. 

Name:	IMG_0887.jpg 
Views:	5 
Size:	430.6 KB 
ID:	157292
    I also encountered a lot of burnt glue which I removed to the best of my ability.
    Thirdly, I replaced two capacitors (C5 & C26) which according to others tend to go back even though mine looked fine. I dont have an ESR meter so wasnt able to confirm whether or not they were actually bad.
    Click image for larger version. 

Name:	IMG_0888.jpg 
Views:	7 
Size:	285.7 KB 
ID:	157293
    I saw a video on youtube describing the MOSFETS as the culprit and decided to check them out. I tested them with my multimeter and they work as intended.

    Currently, I am out of ideas.
    I did have some issues with the soldering and especially around the resistor the board looks somewhat damaged, perhaps from before as the board was darkened a bit. I tested the continuity and it does beep. Do you think it could be an issue?
    Click image for larger version. 

Name:	IMG_0890.jpg 
Views:	8 
Size:	284.3 KB 
ID:	157294

    What would be my next steps? Any help is appreciated.

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 82,712, Level: 70
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,584
    Helped
    4519 / 4519
    Points
    82,712
    Level
    70

    Re: HKTS 220 Power Supply board troubleshooting

    Those two new blue upright capacitors are probably unsuitable. I can see you folded the wire to make radial construction fit an axial footprint and the values might be correct but check they are rated for 105C temperature and are low ESR types. The wrong types will work fine for a while but nowhere near as long as the correct ones.

    Very often on power supplies like that when they refuse to start up but don't blow fuses, it is because the smaller electrolytic capacitors have 'dried out'. Their value gradually drops with age, particularly if they are in a hot environment like a power supply. Usually there is no visible fault with them but their value can drop to almost nothing. It would certainly be worth the small cost of replacing them and they should be readily available. I can't see the part numbers in the photographs but in the middle one I can see three small upright cans near the two you replaced, there may be others out of camera shot. It is unlikely to be one of the other tall ones.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



  3. #3
    Newbie level 3
    Points: 30, Level: 1

    Join Date
    Jan 2020
    Posts
    4
    Helped
    0 / 0
    Points
    30
    Level
    1

    Re: HKTS 220 Power Supply board troubleshooting

    Hi Brian

    Thx for your reply. Yeah i know the blue capacitors are not the ideal solution but it was the only thing i could get at the moment. Unfortunately I dont know where i can locally get the needed parts. I have found several online stores but the shipping costs alone generally tend to be way higher than the actual parts which is quite annoying.

    In terms of the capacitors there are five additional (small) ones mounted on the board. Moreover, there are the larger ones (2x 220MF/200V and 2x 470MF/60V). Do you think it is neccesary to change all of them?
    I was trying to the read the voltage which i assume is the standby yet I only have 3.3v. According to the schematic map, am I reading it corret that it should be 7v (upper right hand corner)? Could that be due to the capacitors?
    Click image for larger version. 

Name:	Schematic map.jpg 
Views:	5 
Size:	181.4 KB 
ID:	157324



    •   AltAdvertisement

        
       

  4. #4
    Super Moderator
    Points: 82,712, Level: 70
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,584
    Helped
    4519 / 4519
    Points
    82,712
    Level
    70

    Re: HKTS 220 Power Supply board troubleshooting

    Capacitors are the most likely cause. All the other parts have long lives but capacitors start to degrade from the day they are made, even if not used although if they are in use they degrade faster. If a voltage is present at all it means there is some life in the primary side of the supply, if completely dead nothing would leave the transformer T1 and all the voltages on the secondary side would be zero. A low voltage generally indicates a capacitor is failing to store charge and what you are seeing is the pulses feeding it rather than their accumulation to a steady level. A meter measuring pulses will give a lower reading than the same voltage but steady.

    You can do a 'quick and dirty' check of the secondary side capacitors by bridging them temporarily with another capacitor. They are not critical of value, especially if it is higher than needed so it is safe to bridge a good capacitor with another good one. If the value has dropped below working level and you bridge it, and the PSU comes to life you have found the problem and only that capacitor needs changing. If you have a capacitor to hand with any value between about 100uF and 1000uF, rated at no less than 16V you can try wiring across each of C3, C5, C6 and C26 in turn to see if it makes a difference.

    WARNING: You stated you are not experienced in electronics so please be extremely careful with this kind of power supply. You will notice that there are no connections between anything on the left of T1 and U2 and anything on their right. They are there for safety isolation. The left 'primary' side will have lethal voltages on it almost everywhere and may not have any isolation from direct wall socket connection whatsoever. The secondary side is considered safe, that is why it can go to consumer equipment. UNDER NO CIRCUMSTANCES EVER link the sides or try to measure a voltage from one side to the other, you could kill yourself. No second chance if you do that!

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



  5. #5
    Newbie level 3
    Points: 30, Level: 1

    Join Date
    Jan 2020
    Posts
    4
    Helped
    0 / 0
    Points
    30
    Level
    1

    Re: HKTS 220 Power Supply board troubleshooting

    Thank you Brian. That was very helpful. I guess I will go ahead and order the neccesary capacitors and try that.
    I just checked the voltage again and there is 3,4 and -4,5. Is that also due to the capacitors?



    •   AltAdvertisement

        
       

  6. #6
    Super Moderator
    Points: 82,712, Level: 70
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,584
    Helped
    4519 / 4519
    Points
    82,712
    Level
    70

    Re: HKTS 220 Power Supply board troubleshooting

    It could be. To be honest it is difficult to tell whether capacitors are working unless you monitor for residual signal across them. A good capacitor will charge on peaks of current and discharge on troughs so giving a stable voltage. A poor capacitor won't be able to store enough so the voltage will fluctuate with the charging current. The only reliable way to check is with an oscilloscope which will show a graph of voltage variation against time. A testmeter will only show the average, if that.

    Adding to the problem is if C5 and/or C6 have dropped in value, the voltage across them will be lower and unstable and it is monitored via the opto-coupler to regulate the primary side drive level. It has a kind of 'cause and effect' feedback making the true fault harder to find.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



  7. #7
    Advanced Member level 2
    Points: 3,827, Level: 14
    Achievements:
    7 years registered

    Join Date
    May 2012
    Posts
    510
    Helped
    118 / 118
    Points
    3,827
    Level
    14

    Re: HKTS 220 Power Supply board troubleshooting

    Check R3 100K to see if it is high in value, put a 1W resistor to replace it if it is. If this resistor is OK then the secondary capacitors having high leakage (and ESR) is the most likely.



  8. #8
    Newbie level 3
    Points: 30, Level: 1

    Join Date
    Jan 2020
    Posts
    4
    Helped
    0 / 0
    Points
    30
    Level
    1

    Re: HKTS 220 Power Supply board troubleshooting

    Hi guys

    So i decided to get all new capacitors as well as changed the diode (D5), as well as replaced the resistor (R3), it wasn't giving me any reading at all.
    Still no luck, and the subwoofer isn't giving me any sound. I checked the voltage again to see if it had reached 7V but now I am having 12V. What now?
    I have also tried to short the PS/ON but nothing seems to happen. I assume that when the signal is there than the power supply jumps into action and delivers juice to the amplifier board through CN4.
    Click image for larger version. 

Name:	Schematic 2.jpg 
Views:	3 
Size:	169.7 KB 
ID:	157391
    Yet when i short the PS/ON I have no reading on CN4 which in general is always Zero.
    Any ideas?
    Thanks



--[[ ]]--