Search results

Search Forums New Posts
  1. KrisBlueNZ

    newbie question - burnt resistor

    Ah, gotcha. It looks like TR20 is supposed to detect overcurrent in the output stage. It monitors the voltage across R72, which is in the emitter circuit of the NPN output transistor. Check R72 and R78. They are supposed to be 0.33 ohms. If they read much higher than that, some (maybe all) of...
  2. KrisBlueNZ

    CRT Sync Symbol

    Oh I think I know what these symbols are. The diagrams represent the image displayed on a CRT and they indicate what the controls adjust. If that's right, the controls are: P1 "FH" - could be field hold aka vertical hold - adjusts the free-running frequency of the field oscillator so it will...
  3. KrisBlueNZ

    HP 1741A Oscilloscope

    Hmm. Those voltages don't entirely make sense. It looks like something is pulling the voltage on Q1 and Q2 emitters down, but it's pulling it towards 0V, not towards -160V which is what I would expect if Q1 or Q2 were shorted or leaky. Can you make a few more measurements please? 1. positive...
  4. KrisBlueNZ

    HP 1741A Oscilloscope

    OK. Here are the measurements I need. 1. Positive lead to R1 east; negative lead to R6 west. (Q1 base wrt 0V.) 2. Positive lead to R3 east; negative lead to R6 west. (Q1,2 emitters wrt 0V.) 3. Voltage across R6 (positive to east end). (Q2 base wrt 0V.) 4. Voltage across R4 (positive to north...
  5. KrisBlueNZ

    newbie question - burnt resistor

    Hi there and welcome to Electronics Point :-) I downloaded the Sansui G-5500 service manual (from hifi-manuals.com) and I can't find either R46 or TR20. The transistors in the power supply section are numbered 600 upwards. Without seeing a schematic I can't say whether you just need to replace...
  6. KrisBlueNZ

    transistor Rbase value

    You need to connect pin 3 to something. If you don't need the sleep mode, connect it to ground. Otherwise it will float and the device's behaviour will be undefined. You also need to connect pin 5 to ground. It is a secondary temperature sense input; if you're not using it, it must be tied to...
  7. KrisBlueNZ

    CRT Sync Symbol

    I don't understand your question. What does the picture represent? What do you want us to do?
  8. KrisBlueNZ

    HP 1741A Oscilloscope

    OK. I can translate those measurements into descriptions with reference to the picture you posted in post #60. First we need to fix the markings of Q2 and Q3 on that picture - you have them swapped over - and add markings for the other components. Can you post an unedited copy of the original...
  9. KrisBlueNZ

    Sony receiver in protector mode. How to check transistors?

    I suggest you buy a digital multimeter. You don't need to spend much - $20 will get you something reasonable. Analogue multimeters are cool but measuring resistance is different from digital meters and it's probably best to avoid confusion. In general when a direct-coupled output stage fails...
  10. KrisBlueNZ

    HP 1741A Oscilloscope

    Perhaps I wasn't clear enough about where to connect the negative multimeter lead. Try this. 1. positive lead to Q1 base; negative lead to 0V (available at bottom end of R6) 2. positive lead to Q1 emitter; negative lead to 0V (available at bottom end of R6) 3. positive lead to Q2 base; negative...
  11. KrisBlueNZ

    HP 1741A Oscilloscope

    Aha! Progress. Can you measure the voltages on the following points with the negative multimeter lead connected to the right hand end of R2 (that is, the bottom end of R4, bottom end of R7, and emitter of the off-board Q2). 1. Q4 base Edit: 1.5. Q3 emitter And can you measure the voltages on...
  12. KrisBlueNZ

    HP 1741A Oscilloscope

    Oh, I see now. There are two copies of the schematic in the service manual! That one is the second one, and it's very clear. The first one is scanned at such a low resolution that it's unreadable. OK, now we have the schematic. Are you able to measure voltages in that circuit? Can you power it...
  13. KrisBlueNZ

    HP 1741A Oscilloscope

    There are many components there that could have failed. The 120V circuit doesn't use an IC; it's all discrete transistors. I've read the circuit description. Without being able to refer to the schematic, I don't find it very useful at all. Perhaps you could try to find vintage electronics...
  14. KrisBlueNZ

    HP 1741A Oscilloscope

    Those markings are probably HP-specific part numbers, used by the actual manufacturer at HP's request. The actual components are probably standard devices, perhaps members of the TIPxxx family, just badged with HP's part number instead of the standard one. If the HP documentation doesn't state...
  15. KrisBlueNZ

    cant play mp4 files saved from youtube

    What? Are you saying there's something inherently wrong with downloading and saving YouTube videos made by other people? I know YouTube don't like it, because they want you to see their advertisements each time you watch the video, but no copyright violation is occurring. Oh, you were kidding...
  16. KrisBlueNZ

    powering a LED help

    LEDs running at 30 mA or less can be powered "directly" from the mains supply using a series capacitor and bridge rectifier. This is normally frowned upon because the LEDs are live, but if it's part of an enclosed product, and you're careful that everything is properly insulated and firmly...
  17. KrisBlueNZ

    Help with light-sensing automatic LED bicycle headlight

    Hi Adam and welcome to Electronics Point! I've had a look at the See.Sense. project and I want to raise a few issues to perhaps save you some trouble. I think the See.Sense light relies on the fact that it flashes in order to sense its environment. If the light is on continuously, it will...
  18. KrisBlueNZ

    Problem with 7 segment display and CD4055

    This may seem like a silly question, but you are using an LCD are you? The voltages needed to drive an LCD alternate constantly over a relatively small voltage range. I don't know the details. But you shouldn't expect the segment and digit output pin voltages to remain stable.
  19. KrisBlueNZ

    Need ALOT of help on an interesting project.

    Perhaps a number of cameras with image processing software, or a large pressure pad at the back end of each parking space. The first option is sure to be cheaper and lower-maintenance.
  20. KrisBlueNZ

    Vaporizing circuit

    Do you mean that the quantity of vapour from the first coil plus the quantity of vapour from the second coil must remain constant regardless of how much vapour is coming from each? If so, you need to know how the coil current relates to quantity of vapour. Below a certain current, the coil...
Top