Quoted from mbwalker:Any chance your have a scope? If so, take a look at the ripple on those lines. You can even check from ripple on the boards ground too (pick up the scope ground at perhaps the power supply, the check the ground at whatever board you are checking).
A little bit of a side issue, but I should probably mention - make sure wherever you add the 470uF, that the circuit supplying the voltage can handle the inrush current from the 470uF. Somewhat obscure, but better safe than sorry.
Floating grounds...I can relate to that. When 1st starting looking at mine, I bet there was only 2 ground screws per board.
I do have a scope and plan on pulling it out. I did watch the DVM on the 18V lamp supply and it was fluctuating a bit so it looks like there is some ripple on that line.
From what I can see on the schematics I don't see any issues with adding a 470uf cap but it is a good point to bring up. I'm going to get to see what the ripple looks like and if the cap helps or not.
There is one ground strap on the lower right side of the head that isn't connected in my Rocky and Bullwinkle. I posted the question in that forum topic to see if someone can get a picture of where those ground straps go so I can attach it to the proper place.
I have all the ground screws in the boards and they are tight. What I am seeing/hearing is that the issue shows up and varies by swapping out some different MPU boards (all other boards are untouched). So that leads me to believe that there is something going on with certain MPU boards that are generating some noise while others not. It seems to be one of the only unexplored areas in this whole thread. If it ends up being the source of noise then I think it would be good to resolve it at the source.
While the DE design of the power, MPU, and sound work I feel that some things are at the limits and right at the margins. If everything is perfect then it may be quite. If not then any of several different things could push it over the edge past where it should be and we get noise.
At the moment I am looking at the lamp matrix since that seems to make noise on some MPU's. I have theories as when the issue could be but it would help to get some data from other DE owners. If you aren't running the extra switching supply I (or of you are and had to) I really need to know what transistors are used in that matrix. Are they TIP42, TIP42C, TIP122, TIP 102, brand ST, Vortex, M Motorola, or something else? It would be interesting to see if there is any sort of pattern.
Maybe a certain brand or batch of parts were just off and although work may cause extra noise.
Anyone have a chance to peek in the backbox and see what is in there??