At my SID-Synth i have the problem, that the SID´s only give a sound at the second power connection.
The Display and LED´s are ok at the first start. When i disconnect the Synth and connect it new, the SID-Modules also ok.
I use the PSU-Poweroptimize option for 8 SID´s.
The voltages i have checked at start. it´s ok. (5,2VDC, 14,2VDC).
I have soldered 2 new Power Optimizer and at this was the same Problem. I have it checked with a new C64 PSU. The same Problem.
Have any a idea?? 
hey good question, i experience the same exact thing w/ my PSU based on TK’s optimized circuit. The only extras i have running is a LCD, 2 banksticks, and a power LED. I am using a c64 power brick to run my MBSID. more details on my build can be found here for comparison: http://www.midibox.org/forum/index.php/topic,10585.0.html
I currently have installed a salvaged 6581 chip but soon i will be putting in a new 6582, perhaps it will make a difference? It doesnt really bother me but I’d like to compare notes and see if we can figure it out. I suspect that perhaps the cap’s in my power brick or PSU circuit need to cycle once to charge & then hit everything w/ proper voltage on the 2nd… either that or the chip needs to warm up or something. Anyone else experience this phenomenon?
edit: I’m certain it has nothing to do with SmashTV’s kit either, it always powered up fine before. I only experience this since building my custom PSU & using c64 power brick.
The problem was, in this moment i have checked, only in self ordered parts. On my SmashTV Part Modules was everything ok. I checked in few days again and solder any new Modules for a difference of tests . . .