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  1. KrisBlueNZ

    CRT TV Board Replacement

    Oh. Do you have a schematic for your original board? Have you removed the filter from the board and measured it? Do you know exactly what is wrong with it? Is there an open circuit winding? Is the adjustable core broken? Have you looked inside it for obvious damage?
  2. KrisBlueNZ

    74hc238 binary decoder info

    Have you connected ALL inputs somewhere? There are three enable inputs (pins 4, 5 and 6) and three select inputs (pins 1, 2 and 3) and they all have to be connected to something. Pins 4 and 5 must be low, and pin 6 must be high, to enable the IC. Pins 1 and 2 must be driven by your Raspberry...
  3. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    You're right, that hole is not going to do any harm apart from cutting out one channel on one input. To fix it, first clean up the crumpled copper. Use a large drill bit, pressed gently into the hole on the copper side, and twist it so it leaves the edges of the hole clean. Or use a razor blade...
  4. KrisBlueNZ

    Nixie Clock

    Have you replaced the MC34063s? They're cheap and still readily available. They would be my first suspect.
  5. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    It's ironic, because there isn't even anything wrong with the loudness circuit! All of these other problems are in other parts of the amplifier. You probably won't find that IC outside of Digi-Key and Mouser. It's not a common component. Standard op-amps aren't suitable because (a) many of them...
  6. KrisBlueNZ

    FunFactory Yooo battery problem

    If you can find an identical replacement battery, great. Otherwise you need to find out what else is in there, apart from the battery. It could just be a fuse of some kind. If you can break it down as far as the internal battery, you should be able to replace that with a generic 500 mAh Li-Pol...
  7. KrisBlueNZ

    Finally got me a 'scope - Have some questions

    "Worn out"? That's not a very technical term. What does he mean? Is he talking about the burn-in? Or does he mean that it's low-emission? Is it dim and out-of-focus? Did he check the filament voltage? Switches can be replaced you know... I was thinking it migh be a bad earth. Have you checked...
  8. KrisBlueNZ

    Fine temperature control (Triac + temperature sensor)

    For power sources use "voltage" and "current" under the main components menu, or "battery" under the "misc" subfolder. Make SURE you put a 0V point (the downward-pointing triangle) on your 0V rail or LTSpice will barf badly.
  9. KrisBlueNZ

    CRT TV Board Replacement

    Wouldn't it be easier to take the chroma filter from the new board and put it on your existing board? Edit: Ask the seller of the new board to tell you the part number of the chroma filter, and if it's the same as the one on the board you have, buy the board, remove the good chroma filter from...
  10. KrisBlueNZ

    how i rewrite a microchip

    Cheertek seems to be a Chinese manufacturer with no web site. If that device is reprogrammable, the information you need to be able to reprogram it is probably not available publically. If a manufacturer wanted to use that device, they would have to contact the manufacturer and sign an NDA...
  11. KrisBlueNZ

    how i rewrite a microchip

    Give us a list of the numbers marked on some of these microchips, or post a photo of some of them.
  12. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    The problem is not that Q519 and Q520 "can't handle" the current. They are being forced to generate about 2.6 watts (total) in heat energy, and I have to assume that the heatsink can't dissipate this energy, because it's getting a lot hotter than it should. The reason why Q519 and Q520 are...
  13. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    OK. The tone control board is drawing at least twice as much current as it should, and this is why Q519 and Q520 are getting too hot. Rather than starting to replace the transistors on the tone control board, I suggest some radical surgery - remove all 18 transistors, and install two ICs...
  14. KrisBlueNZ

    Timing Circuit? Counter?

    You can't really heatsink a SOT-23 package. It will transfer some heat through its legs to the circuit board, and an area of copper around it will help, but you have to limit its power dissipation, otherwise it will overheat. I think your mistake was to choose "Up to 16V" as your input voltage...
  15. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    Right, and right.
  16. KrisBlueNZ

    Fine temperature control (Triac + temperature sensor)

    It's really just the range of resistance, and a gut feeling. You would want the thermistor to vary your conduction angle over most of the 0~180 degree range over a relatively small temperature range, for reasonably accurate control. So you would need an NTC where most of its resistance range...
  17. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    OK. The tone control section is drawing about 50% more current than it should. This could be why the Q519/Q520 heatsink is getting too hot. I missed out some steps from my step-by-steps in post #101. Can you make some more measurements? I want to know the voltages across R555 and R556 with only...
  18. KrisBlueNZ

    Fine temperature control (Triac + temperature sensor)

    I don't have much experience with control loops and PID, but I suspect you don't need PID either. At worst, you could do simple on/off thermostat-type control, but I imagine that any proportional system would give better performance than that, without PID. You could try to control the firing...
  19. KrisBlueNZ

    Nixie Clock

    Hi and welcome to Electronics Point :) As Dave says, it's reasonable to assume that something was damaged by a voltage spike. I would suspect the MC34063s first. It's also possible that the output diodes were damaged; these are connected between pin 1 and the output smoothing capacitor on each...
  20. KrisBlueNZ

    Am I asking the impossible? 12v (input) LED drivers

    Yes, if you're prepared to replace the driver power supply with one that's powered directly from 12V, instead of converting 12V to 120~350V and feeding that into the existing driver power supply, that's tidier and more efficient. But that driver power supply is set up specifically to provide the...
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