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  1. dorke

    Zeroing out a LM317 reference voltage with a zener - PSU build

    I have just seen this thread. Forgive me for not reading it all. Here are a few thoughts : 1. I wonder why do you need to get down to 0-Volts? I know all bench power supplies do get to 0 ,but let me tell you ,as far as I remember. In decades of using various kinds,I have never used one below...
  2. dorke

    Detecting alternating current in my PSU heat sink (leak?)

    Check these things. 1.Resistance between the heat sink and the 3 noted points. 2.The voltages should be stable,see if they drop on the flicker.
  3. dorke

    Check if schematic is correct

    Looks fine the LED is dropping about 2.25V,must be a green led ...;) If it works with the receiver, you need to replace the defective push button.
  4. dorke

    Check if schematic is correct

    Please measure the voltages at the points marked,with the short as you did before. Make the short permanent ,then insert the battery for a short period of time (to prevent damage) and measure.
  5. dorke

    Chip`s plastic protection removing ?

    You should use a hot air heat-gun with temperature control. It isn't very difficult but you should know how to,and there is a risk of damage. look here from 5:08 on. and here from 12:10 on. Also note that if the IC doesn't come off easily it may have it's "belly" glued to the board.
  6. dorke

    Check if schematic is correct

    Is the device actually working with a receiver? Please measure resistance between the 2 yellow circles when the button isn't pressed(no battery).
  7. dorke

    Chip`s plastic protection removing ?

    That is something I wouldn't recommend! Make sure you cleaned the paint remover very thoroughly it can be corrosive and in time may damage the traces on the board!
  8. dorke

    Detecting alternating current in my PSU heat sink (leak?)

    I agree with @duke37 about the bridge being ok if the TV works. Please mark the Caps replaced on the board itself.
  9. dorke

    Clean square waves using a 555 timer?

    Chris, The behavior of the output is due to the fact that the load isn't purely resistive, rather it is a series combination of a largely capacitive one and a resistor. Test 3 in post #61 should show that the IC has no problem of driving it by itself (i.e a "plateau" output).
  10. dorke

    Check if schematic is correct

    Did it work before? If so you can use a short-wire to bypass the switch.
  11. dorke

    Detecting alternating current in my PSU heat sink (leak?)

    Welcome to EP. Gary From the way you speak of current in volts it is obvious you don't have a lot of experience,do you? I would like to worn you of the high voltages found in the area you probed ,400VDC is very common. Take great care! Which capacitors have you replaced and with what kind...
  12. dorke

    Help with Automatic light PCB

    Welcome to EP. What type of LDR are you using? Please measure the voltage on the LDR with a DVM in light and dark conditions.
  13. dorke

    Check if schematic is correct

    This is how I see this. There is a need to measure the switch contacts when it is pressed,can you do that?
  14. dorke

    Clean square waves using a 555 timer?

    I agree with your interpretation. Regarding the current drawn from pin 3 : at point A the current is at it's Max and at point B at it's Min. The higher the current drawn the lower the voltage drop at the output of the 555. The result is you have a ramping exponential-like output level instead of...
  15. dorke

    Clean square waves using a 555 timer?

    Here is another simple test for you: In the "working " circuit , use the same R-C from the" non-working" one as a load between pin3 and gnd. remeasure the signal of pin3 ,what do you get?
  16. dorke

    Clean square waves using a 555 timer?

    Well this must be Collin's view of that "Bad to the Bone" IC. "Wicked" ,isn't it'?;)
  17. dorke

    Digital potentiometer ?'s

    Please post a link to the systems datasheet.
  18. dorke

    search for a Varistor replacement compatibility

    Yes that is definitely a defective Varistor. The explosion black marks are evident in the last 2 photos. That Varistor is a so called "fireproof" type. The outer casing minimized the damage to the surrounding components and indeed minimized the fire hazard due to the exploded Varistor. What I...
  19. dorke

    Clean square waves using a 555 timer?

    "vindicated"? you are too quick to let him off the hook;) Calling the best selling IC(ever?) "nasty", Is ....well, you fill in the dots.:( This wonderful IC is truly ubiquitous (more so than the 32.768kHz watch crystal?). It came out in 1971(45 years ago!) and is still manufactured by about...
  20. dorke

    Clean square waves using a 555 timer?

    You can achieve better results even on the "nasty" breadboard,by following these simple steps . 1. From post #38 "In the case of the non-working (circuit) there is a load(on pin 3) an R-C one, R being 1k. What you can do to get the output a bit higher is use a higher value for R say 33K and...
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