Search results

  1. elebish

    DSP/Amp Problem (Reversed Polarity)

    " Using a Fluke DMM set on the diode setting we get .618 and .468 and when we reverse the leads they both read 0." That should not be! When you reverse the leads to the DMM it should read INFINITE! .618 is ok for the zener D2 and .468 is ok for the protector diode D32. Those are the forward...
  2. elebish

    Hantek DSO5072p Oscilloscope?

  3. elebish

    Hantek DSO5072p Oscilloscope?

    Stick with an analog scope. They are easier to use and will not give you an "alias". I also have an Iwatsu SS 5711D analog that I have been using for many years and it has been one of the best scopes I have ever used. I think I have used them all working in the labs at Boeing for almost 38 years.
  4. elebish

    Negative Voltage - Theory Question

    The ground may just be common but could be chassis ground or earth ground (or both). In the case of USB, there would be a +5 source with a common and 2 pins for neg and pos data. As you know, a USB connector has 4 pins. See https://en.wikipedia.org/wiki/USB
  5. elebish

    Resistor calculation

    One must know the load you are connecting power to and the current that load will draw. You must also know the voltage. Voltage divided by resistance of load equals current. Voltage divided by current equals ohms. This is in dc circuits. Current is expressed in amps. You might want to take a...
  6. elebish

    Hantek DSO5072p Oscilloscope?

    Look on EBAY. I bought a Tek 2465BDM for $550. It's a 400 Mhz with all the goodies. The users manual was still in the plastic bag, unopened. It works perfect and looks new. You can get real bargains but you must know what you are looking for.
  7. elebish

    Tektronix 2215 Help

    This may be normal for this scope. I would check with the Tektronix people.
  8. elebish

    DSP/Amp Problem (Reversed Polarity)

    With a 25 A fuse, you could be in trouble. I would check D34 and D2 for being shorted. D2 is for spikes and D34 could be an input power reversal protection diode which is designed to short out and blow the fuse when power in is accidently reversed. This will protect the unit. D32 should be a...
  9. elebish

    Tektronix 2215 Help

    Almost all scopes above 5 megahertz BW, will dim down when checking progressively higher frequencies. This is due to the higher horizontal sweep speeds and the persistence of the screen phosphor. The better scopes will have a circuit that will brighten the crt when advancing the sweep speeds...
  10. elebish

    Are tantalum caps sometimes used as a circuit protector ?

    Kapp and Collin are right about the low resistance to high frequencies of tantalums, Stick with the tantalum as a replacement.
  11. elebish

    Hello Everyone, Newbie here ! Need help repairing a amplifier.

    Q6 is heat sinked but not necessarily on the chassis. R20 will probably be good unless Q6 has a collector to base short. D14 (1n4004) is suspect since you have dc at the speaker output, assuming the output transistors are good. Check all diodes in fact. Another good idea is to finger test all...
  12. elebish

    Power connector mod - use DC connectors for AC application?

    The current rating is the most important, not whether it is ac or dc.
  13. elebish

    Need a replacement power cord- dont want to burn down house

    18 ga wire is all you need with a good flexible covering and a strain relief at the mixer.
  14. elebish

    garage door opener

    This motor is NOT made for continuous duty!
  15. elebish

    Varistor

    A varistor will change resistance with applied voltage changes. It is also known as a voltage dependent resistor (vdr or an mov) a metal oxide varistor. Most mov's are used for voltage spike protection in ac inputs to electrical appliances. When an ac spike exceeds the rating of the mov, it will...
  16. elebish

    Problems charging a garden tractor battery

    A brother-in-law once connected a 12 volt battery across a 6 volt battery in an old car and the old 6 volt battery blew up and threw pieces of battery and acid all over. Luckily he was not hurt but it could have been fatal. The old battery may have had some ice in it because it was in winter...
  17. elebish

    Sansui SP-2500 Speaker Crossover Repair

    Check phasing in this manner: Apply the dc voltage of a 1.5 volt battery to the speaker input terminals and all speakers in the cabinet should move in the same direction. If not. they are out of phase. Check both speaker cabinets. When speakers within the cabinet are out of phase, one speaker...
  18. elebish

    Need a little help repairing a Toshiba Laptop

    Substitute the power supply to eliminate that as the problem.
  19. elebish

    Are tantalum caps sometimes used as a circuit protector ?

    Tantalums have high capacitance for size but are mainly used in selected circuits because they have an extremely low leakage rate (2 micro amps) at their rated voltage due to the insulator between the dielectrics. They will not take a voltage much higher than their marked ratings and only pass a...
  20. elebish

    Problems charging a garden tractor battery

    If you are using an electronic type pulse charger, it is possible that the battery voltage is too low to accept current from that charger. Try a cheap regular charger to get the voltage up a bit, then hook it back up the electronic charger.
Top