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  1. KrisBlueNZ

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

    Q442 and Q444 are the main output transistors for the right channel. They drive the right speaker. They should be mounted onto a big heatsink. Q441 and Q443 are the output transistors for the left channel. OK, I need more accurate measurements of the voltages across R555 and R556. Set your...
  2. KrisBlueNZ

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

    Right. The wire that goes into CN401 goes off to PCB 9 the tone control board. The wire that goes into CN402 goes off to PCB 10 the "BASCON" board.
  3. KrisBlueNZ

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

    Those are good photos and you've done a good job replacing those components. Everything looks good. Try this. 1. Disconnect CN401 and CN402. 2. Power up the amp and measure the voltages across R555 and R556. 3. Wait to see whether the heatsink gets hot again. 3. Power off, reconnect CN402. 4...
  4. KrisBlueNZ

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

    Don't leave it running if anything is too hot to touch. Are the other eight transistors still getting very hot? Can you upload close-up photos of both sides of the board in the area of the heatsink and the resistors please.
  5. KrisBlueNZ

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

    No, that's not right. It's only Q519 and Q520 on that heatsink, right? And there's 0.43V across R555 and the same across R556? (polarity doesn't matter) And there's about +22V on Q519 emitter and about -22V on Q520 emitter? No, don't reconnect CN403. That would just cause more problems.
  6. KrisBlueNZ

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

    No, that's OK. If you have 0.43V across R555 and the same across R556, that means there is 43 mA flowing through each regulator. That's fine. That will produce about 2 watts total dissipation in Q519 and Q520 which will make the heatsink warm, but not too hot to touch, right? So does the amp...
  7. KrisBlueNZ

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

    OK, that voltage across R556 is too high. It means the current is 470 mA. R556 will be dissipating 2.2 watts and is probably getting very hot! Can you unplug CN401 and CN402 and check the voltage across R556 again. It should be almost zero with CN401 and CN402 disconnected.
  8. KrisBlueNZ

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

    Measure ACROSS the resistor. Disconnect the black meter lead from 0V and put one probe on each end of the resistor. Then repeat for the other resistor.
  9. KrisBlueNZ

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

    Can you measure the voltage ACROSS R555, and the voltage across R556?
  10. KrisBlueNZ

    Help understanding solar lamp circuit

    Hi Colin and welcome to Electronics Point :-) I wasn't expecting to see you here! Please, introduce yourself on the new user introductions forum: https://www.electronicspoint.com/forums/introductions.168/
  11. KrisBlueNZ

    Timing Circuit? Counter?

    Right. Economies of scale, simpler packaging, less material. Manufacturers generally sell small active and passive components on reels of 2000 or more. That's great! :-)
  12. KrisBlueNZ

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

    Hi and welcome to Electronics Point :) Your LED panel lights are specified for an input voltage range of 85~265V AC. This strongly implies that they have a switching power supply inside. Can you see inside? Look for a circuit board that looks a bit like this one: The distinctive features are...
  13. KrisBlueNZ

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

    OK, so is Q908 emitter at around +12V now?
  14. KrisBlueNZ

    Timing Circuit? Counter?

    Yes, that's right. Those regulators need decoupling capacitors - one between the input and 0V, and one between the output and 0V - for stability, so that's three components for each local regulator, but the idea is right. It's not normally done though - normally you have only one regulator for...
  15. KrisBlueNZ

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

    OK. As I said... ... you need to replace R555 again. OK. Good.
  16. KrisBlueNZ

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

    OK. Keep CN403 disconnected. The phono board must have a fault that makes it draw a lot of current, because with it disconnected, your ±50V rails have increased from about ±40V to ±47V. This is good! So you've fixed the problem that was causing R555 and R556 to go up in smoke? Was it caused by...
  17. KrisBlueNZ

    Including libraries

    .h files (header files) are stored in a specific folder on your hard drive. Read the development system documentation to find where they're kept, and make sure that one is there. If it's not a standard part of the development system, you may need to download and include it. The header file...
  18. KrisBlueNZ

    Before all publications went through the marketing department first...

    LOL! That's a bit ironic anyway... Perhaps in the 1970s National Semiconductor was an important company, but since I started in electronic design, I've always associted them with mediocrity. Before they were bought out by Texas Instruments (one of the companies they pooh-pooh in that...
  19. KrisBlueNZ

    Timing Circuit? Counter?

    Yes, you could do that. The 78L05 (http://www.digikey.com/product-detail/en/L78L05ACZTR/497-1184-1-ND/586184) is a three-terminal regulator rated for 100 mA maximum output current. In an application where they are dropping 12V down to 5V, power dissipation restricts the output current to less...
  20. KrisBlueNZ

    mosfet basic calculations

    That circuit symbol is not a MOSFET. It is a JFET. There are important differences. Also, it is a P-channel JFET so the bottom rail of the circuit is positive and the top rail is negative. This is the reason why voltages and currents are negative. This is implied by the "-E" marking but the...
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