Crackle in Marshall VS100

[bnwitt]

I've got one of the early Marshall VS100 solid state amps with a crackle that happens at high signal levels and when tapping the preamp board. At first you could tap anywhere on the board and make an awful noise. I have since found and repaired cracked solder joints at one of the two 12 volt linear regulators ground pin, R21 in the power supply and the reverb return phone jack. Now the crackle can be produced within the area of the regulators and very easily on connector 3 of the preamp board. Connector 2 of the preamp board will produce crackle when tapped but it is so close to connector 3 it might be transference. So, I'm thinking this is a ground issue and I've noticed there is a trace circle made for a wire connection that is marked GN1 on the preamp board with no wire coming from it to ground. All of the circuit grounds from every pc board (signal and power) go to one point on the chassis from the power board. That means the connector wires jumping from board to board are carrying all grounds through all of these connector pins and wires to the power board's chassis grounding wire in a bit of a labyrinth.

My question is have any of you run into issues with these Marshall VS100 amps having bad ground connections at these cable connectors? The customer says the amp has been doing this since it was purchased second hand. I can imagine an intermittent ground while pushing the amp really hard could stress the voltage regulators and there is overheating evidence on the traces connecting them. I'm thinking about connecting each boards main ground trace to the chassis ground point and see if this problem goes away since at this point everything seems to be connector related. Any comments?

[Jazz P Bass]

I would start by reflowing the whole board.

[bnwitt]

Boy that's alot of work for an amp of this value. I'll try that after I add one ground wire from the preamp boad to the chassis.

[J M Fahey]

Going straight to the chassis *might* work (try it) ... or introduce a new, previously non exixtent ground loop problem.
You are re-routing ground in a way not intended by the manufacturer.
I would rather bypass the *connector* suspect by hard soldering (pad to pad, from one board to the next) an extra ground wire following the original path.
Although it might not be a *ground* problem after all; *any* DC carrying connection will crackle if mechanically disturbed.
As a side note, if the customer does find replacing the amplifier cheaper than repairing it, let him be happy.
Do not undercut yourself to meet customer's unrealistic expectations.