Yamaha CS80

> If I plug in the main wire loom into the psu and turn it on, the middle fuse blows immediately
> and I lose the +8.5 and -6.5. If I unplug the main socket into the PSU and turn it on (after
> replacing the fuse it doesn't blow)
>

--- In yamahacs80@yahoogroups.com, "Heath Finnie" <heathfinnie@...> wrote:
>
> If I plug in the main wire loom into the psu and turn it on, the
middle fuse blows immediately
> and I lose the +8.5 and -6.5. If I unplug the main socket into the
PSU and turn it on (after
> replacing the fuse it doesn't blow)
>

I am having the same problem... even worse some idiot had even put a 2.5A fuse instead of the 500mA and it still blows! Did you find out where it shorted, is there a particular place I should start at?  I would appreciate any help I can get!!!

Martin

On Oct 2, 2013, at 4:12 AM, rikard.latvala@... wrote:

I haven´t serviced a CS-80 yet, but on the CS-50 the +8,5 and -6,5 power the
KAS and SH board. Are your CS-80´s recapped and have all new logic installed ?

It should not be a big problem to find which board has the short, desolder the
E, +8,5 and -6,5 set a DVM to continuity test (diode mode) and probe E and +8,5
if there is resistance between these tracks try E and -6,5 if the DVM beeps or gives
a very low reading you will have found your shorted board and the rails that have
a short. Do this test without the power on.

On the CS80, these also power the TKC and two TSB boards and the KBCs.  I spent a lot of time (some detailed in posts here) tracking down a short.  It can be pretty tricky.  The actual short turned out to be old caps on a TSB board that were loading the +8.5v supply.  However, most chips running off the +8.5v don't return the power to ground.  Instead, they go to -6.5v.  Basically, they're CMOS digital ICs running off 15volts, but the 15volts have been shifted down by 6.5volt so that they can handle the audio and CV signals that are +/- around ground.  Anyway, the short on the +8.5v was therefore pulling extra current from the -6.5v supply and actually causing that fuse to blow instead of the +8.5v fuse!

I've now run into shorts on the TSBs on a few CS80s from old caps going bad.  I would re-do the TSBs boards first.  Gavin's kit on eBay is a very convenient way to do this.  You definitely want to have a desoldering tool with a dozen DIP ICs and a couple hundred capacitors to replace.

Good luck!

 David