Vintage Synth Repair

Whenever I encounter hum I check for loose ground connections.

Take care
Arnar

----- Upprunalegt skeyti -----
Frá: "duncan" <ferrograph@...>
Til: vintagesynthrepair@yahoogroups.com
Sent: Mánudagur, 16. nóvember, 2009 20:16:16 GMT +00:00 Monrovia
Efni: [vintagesynthrepair] Re: Crumar Trilogy repair






>>Next there is a another strange problem: 
> When I switch on the unit, after appr. 1-2 minutes there is a hum, that can be heard best in the string section and in the synth section. If I only play the organ section I don´t hear it. 
> 
> The LFO speed is influencing the hum. Very nice effect... 
> 
> If I pull a few of the voice cards, it seems to be, that the hum is lower in volume, and that it is starting after 3-4 minutes after I switched on the machine. 
> 
> What is the problem here?? PSU? Or anything else?<< 

are there power regulation components on any of the voice cards? I don't know the trilogy, but if there are regs or smoothing caps local to each card, these could need replacing. the effect you describe sounds like something loading the supply beyond it's capacity to remove mains hum from the dc. are there any tantalum caps in there? maybe have a feel of the tops of the chips, see if anything's getting warm... 

duncan.