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  1. KrisBlueNZ

    NE555 timer help (newbie)

    Hi Wille and welcome to Electronics Point :-) You're right to connect the white LEDs in series "strings", but you will need quite a high voltage to drive them. What voltage is available on the tractor? You might need a voltage booster, or you might need to change how the LEDs are connected. Do...
  2. KrisBlueNZ

    Will it be safe power more than one LED with this circuit (555 timer,Highpower LED)

    Hi and welcome to Electronics Point :-) Before I answer your question, here are three comments about the design. 1. You should always use a decoupling capacitor on the 555. That is a 0.1 µF ceramic capacitor, or similar, connected between pin 8 and pin 1 as close as possible to the chip...
  3. KrisBlueNZ

    Boost converter 12V to 36V (25 mA load) using 555

    0.5W is plenty. There must be something wrong with your new construction. Try disconnecting the inductor. If RS still overheats, there must be a short (probably to the 0V rail) around RS or RB. If RS is OK now, put the inductor back and disconnect D1. If RS is OK now, check for a short across...
  4. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    Yes you could. But here's a drop-in replacement you can get new from Digi-Key. http://www.digikey.com/product-detail/en/KA78R05CTU/KA78R05CTU-ND/1053731
  5. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    You need a load, such as a resistor between 4.7Ω and 10Ω with a power rating of 5W or higher. If you find one of those, and remove the device from the board, I'll describe how to test it.
  6. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    It's simplest just to try replacing it. If the replacement works, the old one was faulty. If it doesn't, the old one is probably OK. Here's how to connect a 7805 into that position. You need to cross over two of the leads. This will be tricky because they're flat metal, not wires, and...
  7. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    It is possible that IC701 is bad, but not definite. But the original part, Sharp PQ05RA1, is obsolete. You could replace it with a standard 7805 voltage regulator but it is not a drop-in replacement. The pins won't line up, because the 7805 has three pins not four, and two of them need to be...
  8. KrisBlueNZ

    bench power supply

    OK, it's an unregulated supply. So yes, you will need to adjust the supply to get the voltage you want with the load connected. The voltage will vary as the AC mains voltage varies, and depending on the current drawn by the load. If you need an accurate or stable voltage, you should get a...
  9. KrisBlueNZ

    Twin LED Flasher

    The reverse voltage is only small - around 0.5V. Not going to cause problems. I'll check out the link.
  10. KrisBlueNZ

    bench power supply

    Oh. Well, there's something wrong with the power supply. It's a regulated power supply, is it? Do you have a model number or a link to any information on it?
  11. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    OK. I think you'll have to try to follow the current around the board to find the fault. Unplug all the connectors except CN701, turn the board over, turn it on, and find the section of the board that I've marked up in this picture. It's underneath the regulators. Set your multimeter to volts...
  12. KrisBlueNZ

    bench power supply

    Sounds like you're overloading the power supply. The power supply is designed to give you the voltage you adjust it to, but if you connect it to something that draws too much current, that will drag the output voltage down. Find out what output current the power supply is rated for, then...
  13. KrisBlueNZ

    Twin LED Flasher

    Someone else will have to answer those physics questions I'm afraid. I learnt that stuff once but have never used it, and if you don't use it, you lose it! I can explain the astable multivibrator in terms of voltages and currents (I think in terms of conventional current, not electron flow) if...
  14. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    OK, I'm only interested in the LCD end of the CN602 wire. It looks like it goes into a small extra PCB at the top of the photo in post #26, which has some backlighting LEDs on it, I guess. Have a good look at that board and see if there's anything visibly wrong with it. Can you unscrew that...
  15. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    OK, CN602 is the connection from the 5V rail on the main board to the LCD board. It most likely powers the backlight. But there is no information on the LCD assembly in the service manual. Can you take some photos of it please? Especially the place where the two wires from CN602 come into the...
  16. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    OK, that's interesting. So unplugging some of the connectors has caused the IC701 voltage to increase from about 3V to about 4.7V? Can you plug all the connectors back in, check the IC701 voltage has gone back to about 3V, then unplug the connectors one by one and measure the IC701 voltage after...
  17. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    I don't see any tantalums in those photos. Did you find any? Have you checked the underside? Check all the semiconductors on the underside as well. Also try unplugging all the connectors (the two that go to the keyboard, and any others) and see whether IC701 still gets hot. Edit: Except CN701...
  18. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    OK, it's possible that IC701 is faulty, but most likely something is loading the 5V rail down. I can't give you a step-by-step because the service manual doesn't have images of the circuit boards so I can't trace the 5V rail, but you can try a few things. See if you can find any tantalum...
  19. KrisBlueNZ

    Yamaha PSR530 Keyboard, No Display

    OK, obviously there's a problem with the 5V rail. The low voltage on the 3.3V rail will be a result of the low voltage on the 5V rail so don't worry about that yet. The problem with the 5V rails could be IC701 faulty, or it could be an overload on the rail. How hot is IC701 getting?
  20. KrisBlueNZ

    Twin LED Flasher

    Try running it off a 6V supply instead of 9V. The two-transistor astable and monostable multivibrators shouldn't really be run from more than about 6~7V because when one collector goes low, the charge in the connected capacitor forces the base of the other transistor negative, and if this...
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