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  1. elebish

    Connected my oscilloscope up backwards

    Were you ac or dc coupled at the input? What vertical attenuation were you at? Was the input in 'invert" mode? You may not have selected enough attenuation and damaged the preamp. I would suggest removing the vertical amp circuit board and bumping ohmmeter readings of the good channel against...
  2. elebish

    Converting foreign appliances

    The voltage differences could make a significant difference in actual operation, since the output would be about 10% higher due to transformer ratio differences between the primary and secondary. NOTE: Info only. The biggest difference is when a 60 hz unit is powered by a 50 hz supply when it is...
  3. elebish

    Help with Burned out 3000 watt inverter

    I doubt that his inverter could damage the supply coming in through his main breaker which is probably 100 to 200 amps depending on whether or not he is on 120 or 240. He merely 'bucked' an out of phase incoming current if he didn't throw his main circuit breaker to off first. NOTE: Trying to...
  4. elebish

    Strange voltage reading from AC adapter

    Is this adapter an 'ac' adapter or a 'dc' adapter? An ac adapter puts out ac and that is rectified in the computer. A dc adapter puts out dc and has the rectifying circuit in the adapter. Sounds like you have a dc adapter with a bad filter cap or shorted diode. If it is a switching type adapter...
  5. elebish

    Iwatsu SS-5711

    When one gets to be my age, being useful to others is reward enough! Ed.
  6. elebish

    Iwatsu SS-5711

    Replace 19C43 and 19C64 with like values (630 vdc) and readjust 'focus 1, focus 2 and front panel focus. These caps are known to break down with voltages less than rated as the years go by. Ed.
  7. elebish

    Wanted: IF transformer

    I'm looking for a 230 kHz IF transformer (dual slug) for a tube type model number NC-140 HF radio built by National. Ed.
  8. elebish

    Tektronix 2215A

    Most scopes use a brightness enhancement circuit to brighten the trace when the time base switches to higher speeds. Sounds as though your problem is the opposite! I would check the crt cathode voltage at different sweep speeds. The potential should be approx. a negative 2400 vdc. There are also...
  9. elebish

    Oscilloscope Problem

    Remember, a X10 probe is actually a divide by 10 probe and offers isolation between the voltage measured and the scope vertical input of about 10 meg ohms. Ed.
  10. elebish

    Another HP 1741A Oscilloscope!

    Is the defective lvps of your scope a 60hz transformer driven or a switching type supply. Most Tek scopes within the last 30 years will be using a switching type to save weight and cost. They are also more efficient but are more difficult to repair. Some of the resistors used in switching type...
  11. elebish

    Connected my oscilloscope up backwards

    The batteries don't have enough voltage or current to cause damage to an oscilloscope even when connected in reverse polarity to the probe. The probe ground lead is usually connected to scope chassis ground and back to AC outlet ground (common), which is generally connected to earth ground back...
  12. elebish

    Iwatsu SS-5711

    It's a fast switching schottky! Ed.
  13. elebish

    Iwatsu SS-5711

    Let me know if replacing 19C64 and 19C68 fixes your problem. Ed.
  14. elebish

    Iwatsu SS-5711

    I have a 5711 Iwatsu that had the same problem. Replace 19C68 (.01@630v) and 19C64 (.047@630v) on the Z axis board then readjust focus 1, focus 2 and astig. Ed.
  15. elebish

    Iwatsu SS-5711

    Only an old fashion cap checker that checks for leakage at 600 vdc will work. An ESR meter (I have one), will not find this problem, besides they only work on values of 1 Ufd or above. Ed.
  16. elebish

    Iwatsu SS-5711

    You must also replace 19C68 (.01 @ 630 v). They are supposed to be rated at 630 but are marked 600v. This is a common problem in this model scope. Those caps develop leaks at voltages above 200. I just fixed 2 of them. High voltage to this crt anode is 20k, higher than any scope I have used...
  17. elebish

    Iwatsu SS-5711

  18. elebish

    New alternator to car cause relay to buzz - can you help?

    Most car and truck alternators are 3 phase alternators with 2 diodes (for full wave rectification) in each phase. It is possible that one diode in one of the phases is shorted or open, probably shorted. I say this because the relay does not chatter when car is running but does when the ignition...
  19. elebish

    Whole group of LEDs stopped working.

    If the leds are hooked together in series, you may have one led bad. If that is the case, when the leds don't lite when power is applied, read across each individual led with a voltmeter and the led that is bad will read source voltage. Verify that by shorting out that led and the rest should...
  20. elebish

    Hello ,and Help - PCB Track Repair

    You might want to scrape off the carbon deposits created by the burn. Carbon traces will conduct because they act like resistors. Your board is obviously only a 2 layer board. Ed.
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