Mackie 1604 VLZ Pro issues

[Showey]

This is an older mixer and hopefully there is someone here that has had a similar issue.
Channel 4 is pretty much dead, several of the others are weak (as compared to eachother or my old CR1604) and there is scratching noises at times when all else is silent, and the right side bus is down 10db.
I have found that if i push down on top of the board near the mounting screw near channel 5, the scratching noise stops or comes on / changes etc. and ch 5 will get very loud (probably normal output).
similar thing if the same spot near ch 7 pressure is applied.
I had it apart for cleaning bu I really didn't SEE anything. I was hoping to see a cracked solder joint or something along those lines but I may have missed it.
Any thoughts or similar experience with this board?

[petemoore]

"This board''...no...but boards as a wider topic would be appropriate I think.
With that I have some experience.
I have found that if i push down on top of the board
Whenever this happens and other things that would be problem or intermittent problems [the hardest to find solutions for, IMe] are associated with the board moving.
This can mean a number of things, and can occur in a large number of place [boards have many places for problems to occur]:
A broken trace, unlikely unless it was physically bent and stressed to that point.
A piece of something which doesn't add a jumper when the board is pressed on, also unlikely, especially when jacks that seal the holes are used.
A cold solder or somehow otherwise compromised solder point.
Anything else...and can be hard to find. If you can find a voltage or connection change associated directly with what 'fixes it' [pressing on the board], it is pretty certain you've located the area which may need repair.
First inspect for exposure to say liquids, anything sticky or look like there may have been a 'river' at one time ? A foreign object of the smallest type may be enough to add a connection.
But I've also had channels go dead for a reason [such as railing the input with the gain up, such as when plugging something in], and, for no reason at all.
We're not really working on a very similar board [about the same thing I expect except more channels, and maybe a different feature or two], this isn't mine and stays in the rack mount though. If barked into, it pops on for a while.

[Enzo]

And any channel with an insert jack, the insert jack itself is immediately suspect. it is like an effects loop send and return in one jack. When not in use there are internal contacts that connect tip to ring. Those get dirty and you lose signal. I have a TRS plug wired tip to ring here on my bench, I use it to plug into insert jacks to test this very thing.

[oc disorder]

Had one with failed smd chips in the channels.
Not one of my favourite repairs. Used a thermometer to find the ones with elevated temperatures (yes got desperate ! ) and after a deep breath and some tlc managed to replace them and all worked fine !
This had got to the point of shutting down the power supply so the temperature trick may not work. A can of freeze applied carefully to suspect chips while monitoring the output may be helpful.
Fader cleaner may be useful too !

[martinnez]

i've had some with bad conectors from the main board to the input board,and those that come with ribbon cables also have sometimes bad solders at either side, they behave like that making false contact now and then. resoldering and or cleaning solved that!!

[jrfrond]

Ribbon cables are a major source of headaches in those units. You may need to just reseat them, clean them (using DeOxit or ProGold) or even squeeze the crimp tighter on the connectors, usually all three. Before you do ANYTHING else, make sure that all interconnects are good, because there is a good chance that's your entire issue.

[mozwell]

If you need a schematic there is one at Professional Mackie : Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
If its not there now, it should be there within a few days

or email me at andymac1962 aaattt hotmail dddooottt com & i will send it