Why test button no worky?

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76nemo

76nemo

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Ogdensburg, NY
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You may not be able to tell by the picture, but the transistor has a hole blown in the side of it. As you can tell, work is slow, so I took the time to disassemble this to see just what let go. I should of snapped some pics of all the spiders nests in it before I cleaned her up:roll:
 
76nemo

76nemo

Senior Member
Location
Ogdensburg, NY
quogueelectric said:
Ma`am you have a spider situation here. I have heard it all now.
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Never said it had anything to do with spiders. I'd have to say it was a matter of a box in a very wet location not properly sealed, there again, by the age and abuse the device has seen, I couldn't pinpoint it to moisture, but I'd have to guess it played a good role:roll:
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
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76nemo said:
You may not be able to tell by the picture, but the transistor has a hole blown in the side of it.
Click to expand...
Don't look now, but that's a full-wave bridge rectifier (i.e., four diodes.) Note the two sine waves and the + on top.

The waves are directly over the AC input terminals, the DC+ output is under the +, and the unmarked one is the -.
 
G

gar

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76nemo:

In the second photo the black object you are pointing to is probably an SCR. But I do not see it in the first photo.

In the first photo you are pointing at a 15,000 resistor with a burn spot. A 15,000 ohm resistor would logically relate to the test resistor. However, the orange strip looks more red on my monitor.

Just above this resistor is a white object that may be a capacitor. Above the white device is where the black SCR of photo 2 should be. But whatever is in that spot does not look black or have the top shape of a TO-92 package.

If the SCR failed open or the trip coil, then operation of the test function would keep power applied to the 15,000 ohm test resistor and thus cause it to burn out. 120 V applied to a 15,000 ohm resistor is close to 1 W. The test resistor is probably a 1/4 or 1/2 W rating.

Where is the trip coil and mechanism and how does this circuit connect to the trip coil?

Is the trip coil burned? And is it now an open circuit?

Most likely failure of the SCR would be to short, and this could very well blow a hole in the package.

.
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
gar said:
In the second photo the black object you are pointing to is probably an SCR. But I do not see it in the first photo.
Click to expand...
The second photo is taken from about the 10:00 position in the first pic. That is a bridge rectifier he's pointing at in the second. The pen in the first pic is just propping the PCB board against his Ideal tester.

In the first photo you are pointing at a 15,000 resistor with a burn spot. A 15,000 ohm resistor would logically relate to the test resistor. However, the orange strip looks more red on my monitor.
Click to expand...
I believe that is a 1.5K resistor, and part of the low-voltage DC supply circuit, along with the bridge and the cap you identified.

Just above this resistor is a white object that may be a capacitor. Above the white device is where the black SCR of photo 2 should be. But whatever is in that spot does not look black or have the top shape of a TO-92 package.
Click to expand...
No, the bridge he's pointing to in the second pic is behind (at that angle) the resistor and cap. There is a TO-92 transistor (or may be a low-power SCR) with a painted flat face directly above the cap. It's between us and the bridge in the second pic.

If the SCR failed open or the trip coil, then operation of the test function would keep power applied to the 15,000 ohm test resistor and thus cause it to burn out. 120 V applied to a 15,000 ohm resistor is close to 1 W. The test resistor is probably a 1/4 or 1/2 W rating.
Click to expand...
The large resistor is a 1- or 2-watt unit. For reference, the resistor next to the 8-pin DIP IC is a 1/2-w unit. The "test button no worky" because the circuit has no power supply. It would not respond to a real accidental shock in use, either.

Where is the trip coil and mechanism and how does this circuit connect to the trip coil?

Is the trip coil burned? And is it now an open circuit?

Most likely failure of the SCR would be to short, and this could very well blow a hole in the package.
Click to expand...
The coil and output side of the contacts (receptacle and feed-thru terminals) are on the other half of the receptacle, not shown in the pix.

Possibly, but that shouldn't damage the power supply, which is not in line with the power circuitry.

My guess is a high-voltage spike blew out the supply, or something in the circuitry has shorted downstream of it.
 
G

gar

Senior Member
Location
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Larry:

You did a much better job of looking at that circuit than I did.

The resistor band did look quite red, and I should have compared the resistors sizes.

.
 
76nemo

76nemo

Senior Member
Location
Ogdensburg, NY
LarryFine said:
Don't look now, but that's a full-wave bridge rectifier (i.e., four diodes.) Note the two sine waves and the + on top.

The waves are directly over the AC input terminals, the DC+ output is under the +, and the unmarked one is the -.
Click to expand...



Maybe I should go back to the "Certified Dummy" signature if you don't think I know what different bridges look like:roll: I am pointing at the TO-92 package, not the bridge. My camera sucks:cool:
 
76nemo

76nemo

Senior Member
Location
Ogdensburg, NY
gar said:
090309-0657 EST

76nemo:

In the second photo the black object you are pointing to is probably an SCR. But I do not see it in the first photo.

In the first photo you are pointing at a 15,000 resistor with a burn spot. A 15,000 ohm resistor would logically relate to the test resistor. However, the orange strip looks more red on my monitor.

Just above this resistor is a white object that may be a capacitor. Above the white device is where the black SCR of photo 2 should be. But whatever is in that spot does not look black or have the top shape of a TO-92 package.

If the SCR failed open or the trip coil, then operation of the test function would keep power applied to the 15,000 ohm test resistor and thus cause it to burn out. 120 V applied to a 15,000 ohm resistor is close to 1 W. The test resistor is probably a 1/4 or 1/2 W rating.

Where is the trip coil and mechanism and how does this circuit connect to the trip coil?

Is the trip coil burned? And is it now an open circuit?

Most likely failure of the SCR would be to short, and this could very well blow a hole in the package.

.
Click to expand...


Yes gar, it is a TO-92 package, a Motorala with MX28963I47 stamped on it, with a nice big chunk blown out of it. It does not read shorted although. What looks like a burn mark in the 15K resistor is actually not, it reads fine and is 1W. And yes, it is an open circuit.
 
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LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
My apologies

My apologies

76nemo said:
Maybe I should go back to the "Certified Dummy" signature if you don't think I know what different bridges look like:roll: I am pointing at the TO-92 package, not the bridge. My camera sucks:cool:
Click to expand...
Sorry. I looked closely at both pics, and it looks like you're pointing at the bridge in the lower pic.

No insult intended.
 
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