Low staticky crackle on right channel (solved)

[Julyan9]

I'm running out of ideas what to do I did the grounding test.

Measure resistance through this grounding path:


It jumps to the 2 left lugs of the volume pot, measure both lugs.  Then it jumps to the back to the RCA jacks.  Measure to the outer jacket of the RCA jacks.  OK

From the top left lug of the volume pot there is a grounding jumper to the two bottom lugs of the headphone jack.  The jack in the picture may be different than what is being delivered today.  Measure to both headphone jack lugs. OK

The power supply ground comes from those bottom headphone jack terminals to terminal 12.  Measure to terminal 12.  From there it jumps to terminal 14 and ends at terminal 20.  Measure to both. Cant get a reading from bottom hp jack terminals to 12. 12->14 also blank and 14->20 too. Ground ok from hp jack lower terminals to 20

Also from terminal 3 you go to the center lug of the 9 pin tube socket.  This is the ground route for the LEDs in the cathode circuits.  Measure here. OK

The heater (AC) supply gets its ground from a wire from transformer terminal 4 to terminal 22.  Measure both. This I didn't understand, 4->22 gives no reading but what is supposed to be the starting point of this.

Other points that should be a solid ground are pin 8 of the large tube, pin 4 and 5 of the small tube, T8, T11, T14, T16, T17, T20, T22 and the ground post on the IEC power connector, the one with the bare wire to the chassis. OK if i did this part correctly

[Paul Birkeland]

Cant get a reading from bottom hp jack terminals to 12.

These are connected by a piece of wire.  If they don't measure as being connected by that piece of wire, then you have a solder joint at one end or the other that isn't doing its job. It's very common for the solder joint on the headphone jack end to not flow around both wires, so I would check there.

The heater (AC) supply gets its ground from a wire from transformer terminal 4 to terminal 22.  Measure both. This I didn't understand, 4->22 gives no reading but what is supposed to be the starting point of this.

What version of the Crack do you have? (If there's green wire in it, it's the newest one).  The 6.3V AC winding gets its ground from the ground lug back by the IEC power entry module unless you have a previous version of the kit.  The place to measure this reference would be B7 and B8.

[Julyan9]

HP jack to 12 is fixed now, i still cant get anything from 12->14 or 14->20 but hp jack to 20 works fine.
Also from IEC ground lug to B7 and B8 is ok

[Paul Birkeland]

Consider reheating and flowing those joints to get good ground continuity throughout.

[Julyan9]

Could that also help with the sound on other channel or are those two completely separate issues?

All grounds are good. Don't tell anyone I was trying to measure them from the transformer instead of the terminal strips 

Attached a pic of the HP jack as of now. Im going to reflow everything one last time and see if that helps.

Left the amp on overnight again, same thing happens . When I use the amp normally and it's on like 4-6 hours the sound is barely noticeable. When I leave the amp on overnight and it has time to warm, the sound is very prominent after.

edit no5. Again I reflowed over the whole circuit with 0 change

[Julyan9]

I was wiggling B4 and B1 and reflowed B4 and that sorted out B4. Swapped the whole wire from B1 to L1 since both ends looked a bit scuffed. Poking at the joints doesn't affect the sound anymore but its still there like before.

[Paul Birkeland]

The next thing to do is to find a wooden chopstick and a cheap pair of headphones.  With the cheap headphones on and plugged into the amp with the amp upside-down, poke around the amplifier with the wood chopstick until you can activate the noise, then you'll know where the issue is.

[Julyan9]

The next thing to do is to find a wooden chopstick and a cheap pair of headphones.  With the cheap headphones on and plugged into the amp with the amp upside-down, poke around the amplifier with the wood chopstick until you can activate the noise, then you'll know where the issue is.

Yeah I've been doing that for days. The noise is not there all the time and some times very faint. I cant find any more connections that make it come or go. I've fixed all I thought were the issue but apparently werent. Could be any of the red wires. I go all the red ones over once more.

[Paul Birkeland]

If the noise is not persistent, it would be a good idea to look into external sources. For example, any appliance with a motor in it (fridge, washing machine, dryer, bathroom fan) or a switching power supply can set things off.  Your phone and/or wifi router can also broadcast periodic noise that can get into components. 

Generally folks find it helpful to take their amp to a different location (office or a friend's house) to see if it behaves in the same way in a different environment.

[Julyan9]

Did all the red ones again for the tenth time. Still the same. Yeah its not persistent. Sometimes the amp can be silent for a couple of minutes or more before it happens again. Make the chopstick test very difficult.

I tested it in another room and switched off wifi. Still there. If I don't get this to work during the weekend I'm just going to send it back and pay for the repairs. I will be baffled if its still a cold solder when I have reflowed all joints 10 times and swapped couple of the wires.

[Julyan9]

With speedball installed should I still get the 2.9K ohm resistance from 12U to B3 and B6? I cant get a reading anymore. Same goes for 12U to terminal 7 and 9. It passed the test earlier.
Also from 12U to Left RCA center pin I get 115 but to Right its 122.5

I may be grasping at straws here but I'm running out of ideas

Took new readings from the Speedball circuits aswell (havent touched these since the problem was even before speedball, which i realized only after I installed speedball, thought I fixed it before)

Large Board OA 63.7 OB 60.7 G 0 B+ 137.7
Small Board OA 33.8 IA 138 B-A/B 0 to 1 IB 137.7 OB 37.5

These are by using 234V wall socket

[Paul Birkeland]

Your boards are not working properly.  Getting 38V out of the small board is likely the root cause of the problem.  Your high voltage rail is also low.

Can you pull the 6080, leave the 12AU7 in, then let me know what the OA and OB voltages are on the small board?

[Julyan9]

OA 28, OB 31

[Paul Birkeland]

Flip that board over and resolder all of the solder joints, especially on the MJE350.  Can you post some photos of that area of the build?  Are the LEDs on the socket lighting?

You're only passing about 1/3 of the current through the small board that you should be.

[Julyan9]

Yes sir, all the LED's are working, the ones on the small board seem a bit dim though. I will go over the small board now and measure again after

Went over the soldering, IB and IA got up to 175 now but OB and OA are the same as before.

Edit. Tried to reflow the center legs again couple of times to no avail. The solder moves around the leg but the numbers are the same from OB and the center leg