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Subject: Re: [yamahacs80] CS-80 loss of +8.5 and -6.5 voltage on PSU

From: David Rogoff <david@...>
Date: 2014-01-16


On Jan 15, 2014, at 12:47 PM, <nightmusic1974@...> <nightmusic1974@...> wrote:

Hi everybody, i'm new to this group, and it happens that i have the exact same issue with +8,5 and -6,5 for a few days now.I would follow Heath Finnie procedure by replacing IC722, and both 1000uf caps.I would also check TR09 and TR14 as you suggested Christof, but where do you find those ones? i dont see them on the SVU circuit board and wiring? (http://therogoffs.com/cs80/manuals/CS80_Service_Manual/60%20-%20SVU%20Circuit%20Board%20&%20Wiring.jpg)

Welcome to the group!   As to the +8.5/-6.5 supplies, I’ve always found the problem to be a semi or hard short, usually one of the caps on the TSB boards.  It’s possible it’s the op-amp or transistors in the PS, but I haven’t run across that.  As to where TR9 and 14 are hiding - they’re on the heatsinks, not on the PCB.  I can’t remember right now whether they’re the big TO3 transistors or (I think more likely) the TO220 transistors.  If the latter, they’re a massive pain to get to!!!

Good luck and let us know what you find.

 David