Zapped by Crack! FIXED!

M

monsterdonkey

New member
I finished my Crack today. I did the voltage checks and visually inspected all of the solder points.

Plugged in the 'phones...I got though one song and got some crackling. I thought maybe the 12AU7 was a little dirty. I cleaned the tube pins with Deoxit and fired it back up. The crackling may or may not have gone away I didn't have it on long enough to find out. When I attempted to wiggle the headphone jack I received a mighty jolt!
Needless to say I immediately powered down but since then I haven't touched the machine. I wonder if I didn't allow the Deoxit to evaporate completely and shorted something? I'll go in and really try to find a cold joint or something touching something else. Fuse not blown. Ouch.

A thing, since the jolt the volume is gone and with the power off I can faintly hear the signal through the headphones.
 
monsterdonkey said:
I finished my Crack today. I did the voltage checks and visually inspected all of the solder points.

Plugged in the 'phones...I got though one song and got some crackling. I thought maybe the 12AU7 was a little dirty. I cleaned the tube pins with Deoxit and fired it back up. The crackling may or may not have gone away I didn't have it on long enough to find out. When I attempted to wiggle the headphone jack I received a mighty jolt!
Needless to say I immediately powered down but since then I haven't touched the machine. I wonder if I didn't allow the Deoxit to evaporate completely and shorted something? I'll go in and really try to find a cold joint or something touching something else. Fuse not blown. Ouch.

A thing, since the jolt the volume is gone and with the power off I can faintly hear the signal through the headphones.
Click to expand...

If I were you I'd do a thorough visual inspection like you said.  Then do the resistance checks and voltage checks again. 

You're also getting power to ground if the chassis nailed you so look close at things like two tube socket pins touching each other.  Or maybe an untrimmed lead somewhere.  Also look at all the ground points like where the terminal strips bolt into the chassis and make sure you didn't accidentally wire a hot to ground.

Probably two tube socket pins touching or something.  I doubt too much deoxit would direct short you to ground.

John
 
Agree with John... Do the voltage checks. If its wrong, post your findings here. PB can probably tell you whats wrong. Something is definitely not right..
 
Here are the readings I've taken, cold and hot. I found one unattached wire: the black where it first attaches to the volume knob was cold. I reheated the biggest joints and anything that looked suspicious. One thing I did was follow the revision that attaches power transformer 4 to 14U instead of 22L. It's crowded in there so I reheated all that. Also I'm not using the stock output caps yet (mine are in the mail) I've got 100uF 250V in there instead for now. This isn't the problem is it?

The tubes are lit, the LEDs are lit, no wires or pins touching where they should not.. I don't know how to test for electrocution potential without actually being electrocuted.  :o  Play time is over for now. I'll check in tomorrow.

COLD k ohms
1=O.L
2=O.L
3=0
4=O.L
5=O.L
6=2.47
7=2.95
8=0
9=2.9
10=2.4
11=0
12=0
13=up to 335
14=0
20=0
22=0
B3=2.9
B6=2.9
RCA JACKS
GR=0
RED=108
WHT=100

HOT VDC
1 = 74
2 = 161
3 = 0
4 = 161
5 = 79
6 = 0
7 = 99
8 = 0
9 = 102
10=0
11=0
12=0
13=161
14=0
15=182
16=0
17=0
18=80
19=76
20=0
21=201
22=0

A1=79
A2=0
A3=1.5
A4=0
A5=0
A6=74
A7=0
A8=1.5
A9=0
B1=74
B2=160
B3=99
B4=79
B5=161
B6=102
B7=0
B8=0
 
Your voltages look good.  You've already done the tests to see if you'll get nailed.  Some of those voltage checks are to ground.

Just to be safe set your meter on AC and then DC and simply place both leads on the chassis.  If you get 0V you can manhandle it all you want.

If your LED's are all lit and your voltages are on you're probably making music.

John
 
It works. I'm going to bet on that loose connection I found and hope for no more shocks. When I finally put on some music I had no left channel. What now? Oh, loose connection on my HD600s.  :D

Thanks everyone!

Rob
 
I have been here for 10 years.  You are the only "shock" I can remember.  But memory isn't what it used to be.  The wire on the volume control only carries 1 or 2 volts maximum.  You couldn't feel that. 

The wires that can shock are the incoming AC wires and the output of the transformer that goes to the diodes.  Those last wires are not likely to touch the chassis plate.  I would check that none of the wires I mention don't get too close to the chassis plate.  BTW, the ground lug is supposed to touch and be "bonded" to the chassis plate for your protection.
 
Yes there is a fundamental connection on the amp that MUST be checked. Make sure that your safety ground screw has the proper connections, and make sure that the outlet you have plugged the amp into has been wired properly and that the third, ground wire in it is actually grounded. While it is possible to get a shock by reaching into a live amp and touching certain terminals (and this is why we give very specific safety instructions when you get to the testing part of the assembly manual) the chassis and power transformer should not be able to be live when connected to a properly wired outlet.

Unplug the amp from any outlet, leave the power cord attached to the amp. Set your meter to a low ohm setting, or better yet switch on the continuity beeper if you have that setting. Touch the black lead to the third, grounding prong on the power cord plug. Touch the red lead to the chassis plate where there is no insulating material like paint covering it. Make sure you see a very low reading, like 3 ohms or less, or that your continuity checker beeps. Also check the power transformer end bell the same way.
 
The continuity test checks out. I'm going to ride over to one of our home improvement centers this evening and pick up a 120V circuit tester. This house is 100 years old and it has been electrically updated but who knows for sure how well.
 
Save the dough, just use the meter you have.

Line to neutral should be same as line to ground.

If you have any voltage neutral to ground, you have a problem.
 
BTW, to follow Mike's suggestion above you need to know that the larger opening is neutral, the smaller one is hot (line as he says).
 
  I assembled and installed the Speedball upgrade yesterday. It didn't go completely smoothly. The first test had one of the LEDs on the 12AU7 not lit. Then others did not light. Those damn LEDs are great for alerting the builder to trouble. I love how I mangled the wiring and didn't blow anything up. It works perfectly now.

  A few problems I had: Where a wire is attached to the pad marked I on the small boards, near the I pad  ??? there is a pad marked - which I guess could look like an I when tilted over. I soldered a lead there. On the second board I got the correct pad but I switched the two red wires. The third problem was while checking for loose connections etc I snapped a few wires off where I had scored them too deeply with my knife using Herculean strength to cut the casing off. Teflon is heat resistant, not cut resistant.

  The troubleshooting process was fun though. Once you stare at the thing long enough it starts to make sense. Rock on!
 
monsterdonkey said:
  there is a pad marked - which I guess could look like an I when tilted over.

I snapped a few wires off where I had scored them too deeply with my knife using Herculean strength to cut the casing off. Teflon is heat resistant, not cut resistant.
Click to expand...

Yeah one should always check one's work against the photos as well as the written instruction.

The proper tool for stripping wire is a - you guessed it - wire stripper. Make sure to use a gauge setting that does not nick the copper right where the insulation is cut. We hear about that happening a lot to customers. People will go on and on about their solder stations and their DMMs, but I think an equally important place to invest in really good tools is your wire stripper and side cutters. You will use them a heluva lot more than the meter.
 
But...but...but...the multimeter is digital!!! All things digital are cool and valuable and worth spending a lot of money on. Not something as mundane as a wire stripper or side cutter...[sorry, had to stifle a yawn there].

:P ::) ;)
 
It is true. My current wire stripper/crimping tool is old and cheap, like a dollar store type of thing. It has a few notches for stripping a few different gauges but not for wire as thin as this. On the list!

I found myself kind of skimming the instructions, hence the errors.. It's my learning style. Wreck the first one and clean up from there. As long as I'm not committing open heart surgery. But still, silly mistakes like that can be costly. I used to work in a lab at a high tech machinery factory. Engineers would design something and I would attempt to put it together. A mistake was sometimes seen as a positive thing because it would help us head off potential production line problems in the future. Mistakes like attaching wires to the wrong places despite clear instructions were just embarrassing.

rm
 
I'm such a cheap bastard I refuse to get rid of my favorite wire stripper because its getting dull. I'm trying to figure out how I can sharpen it! Thats sick! Right?
 
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