C4S Board LED on and off every 5-10 minutes [resolved]

[prtuc2]

Hi guys, I been having trouble with my crack with speedball upgrade for a while. The problem started when I plug in my headphone into the headphone jack like a year ago. So, at first I just spin the headphone cable the cracking sound would go away then every 5 minutes or so the crackling sound would start on again. I didn't have time back then, so I left it be.

A few days ago the new 12AU7 tube arrived, thinking perhaps the tube might have been bad. The problem continues as the new tube was being replaced. Then, I was looking to re-solder some joints near the headphone jack area and the RCA connector. Tighten up the RCA nuts. Problem still remain unsolved and this morning as I was doing some measurement for the amp here is what I got for the resistance values that didn't match the manual:
Terminal 7             2.9k Ohms ----- (OL)
Terminal 9             2.9k Ohms ----- (OL)
B3                        2.9k Ohms ----- (OL)
B6                        2.9k Ohms ----- (OL)

basically, all the 2.9k Ohms terminals in the manual I got OL reading.

Then I took the VDC readings for each terminals
1                          66.1V
2                          170V
3                          0
4                          170V
5                          66.1V
6                          0
7                          95V
8                          0
9                          97V
10                        0
11                        0
12                        0
13                        165V
14                        0
15                        184V
20                        0
21                        206V

Here is the strange parts when I was taking the reading, terminal 1-5 need constantly holding in different positions to get reading then I realized the C4S board led on all 3 boards were not ON. I move the capacitors on terminal 7 or 9 or wiggle the terminal 6-10 strip then the LED came back ON and I retake the values on terminal 1-5 now is just a tap no need to reposition multiple times for a reading.

As I plug in my headphone after 5 minutes the static, crackling sound is back again then I look at the C4S LED on the board it were OFF then I press on the top metal plate at the headphone jack/ volume knob/ input tube area the static went away. If I let my hand off the metal plate static comes back again.

Is it a loose connection or soldering problem? I am kind of confused. Thanks in advance for any inputs everyone.

[Paul Birkeland]

If moving the headphone cable around makes a difference, you have a loose connection.  It's ultra common to have a loose wire where the two black wires meet on the headphone jack.

The resistance measurements you took are from the stock Crack manual with 3K resistors.  You will not get a 3K reading on 7/9/B3/B6 with the Speedball installed, that's normal.

The voltages you posted are totally fine and would likely change if you disturbed the loose connection. 

[prtuc2]

I recheck the headphone wires everything is solid no loose part. I should say that after I tighten up and re-solder moving the headphone cable around didn't make a different in the crackling sound. Now, only the holding down the metal plates or moving the strip from terminal 6-10 can turn on the LED light.

[Paul Birkeland]

I recheck the headphone wires everything is solid no loose part.

Please reheat every solder joint in your amp other than A3, A8, and the power switch.  You still have at least one loose joint.

[prtuc2]

Thanks Paul, re-solder all the joints seem to fix the problem.