Yamaha StagePas

Did I read somewhere that it's inadvisable to use metal bodied jacks on
the amplifier module outputs as the left and right grounds are at
differing potentials?

Or did I imagine that?

Ron(UK)

Ron wrote in message
...
Yamaha StagePas

Did I read somewhere that it's inadvisable to use metal bodied jacks on
the amplifier module outputs as the left and right grounds are at
differing potentials?

Or did I imagine that?

Ron(UK)

That is the 500 has an inverted channel, 300 is nomal,
circuits etc on eservice for both.
the 300 PA units are , AFAICS, the same as the 500 including overlay numbers
just scaled component ratings , detailed in that manual.
As it happens moving from bench testing a 300 PA to powering properly in the
chassis.
Check the state of the fans while at it, see thread a week ago "white
coating ..."

Ron wrote in message
...
Yamaha StagePas

Did I read somewhere that it's inadvisable to use metal bodied jacks on
the amplifier module outputs as the left and right grounds are at
differing potentials?

Or did I imagine that?

Ron(UK)



Beware of topside solder (double sided board) of drain of Q7109 , crosslink
to Q7103 , both powerFET. Have to remove large C2124 rather than removing
the 30uH to get to that solder point
R3114 , not labelled on overlay of the 300 is 1K , not 470R as the 500

"Ron" wrote in message
...
Yamaha StagePas

Did I read somewhere that it's inadvisable to use metal bodied jacks on
the amplifier module outputs as the left and right grounds are at
differing potentials?

Or did I imagine that?

Ron(UK)



Yes, I said that.


But particularly metal right angle jacks that are almost bound to end in
disaster.


Gareth.

On 13/04/2011 19:16, Gareth Magennis wrote:


"Ron" wrote in message
...
Yamaha StagePas

Did I read somewhere that it's inadvisable to use metal bodied jacks
on the amplifier module outputs as the left and right grounds are at
differing potentials?

Or did I imagine that?

Ron(UK)



Yes, I said that.


But particularly metal right angle jacks that are almost bound to end in
disaster.


Gareth.

Ah thanks Gareth, I checked the circuit diag and yes the two amps are
'out of phase' I`ve been asked a couple of times to make short link
cables with right angled jacks for the 'docked' amp to its own speaker.
I`ll have to warn customers in future.

Ron

"Ron" wrote in message
...
On 13/04/2011 19:16, Gareth Magennis wrote:


"Ron" wrote in message
...
Yamaha StagePas

Did I read somewhere that it's inadvisable to use metal bodied jacks
on the amplifier module outputs as the left and right grounds are at
differing potentials?

Or did I imagine that?

Ron(UK)



Yes, I said that.


But particularly metal right angle jacks that are almost bound to end in
disaster.


Gareth.

Ah thanks Gareth, I checked the circuit diag and yes the two amps are 'out
of phase' I`ve been asked a couple of times to make short link cables with
right angled jacks for the 'docked' amp to its own speaker. I`ll have to
warn customers in future.

Ron


I don't quite understand how such designs ever make it to production.


Gareth.

On 13/04/2011 21:20, Gareth Magennis wrote:


"Ron" wrote in message
...
On 13/04/2011 19:16, Gareth Magennis wrote:


"Ron" wrote in message
...
Yamaha StagePas

Did I read somewhere that it's inadvisable to use metal bodied jacks
on the amplifier module outputs as the left and right grounds are at
differing potentials?

Or did I imagine that?

Ron(UK)



Yes, I said that.


But particularly metal right angle jacks that are almost bound to end in
disaster.


Gareth.

Ah thanks Gareth, I checked the circuit diag and yes the two amps are
'out of phase' I`ve been asked a couple of times to make short link
cables with right angled jacks for the 'docked' amp to its own
speaker. I`ll have to warn customers in future.

Ron


I don't quite understand how such designs ever make it to production.


Gareth.

Probably because they aren't designed by the people who use and abuse
them.

Ron

Gareth Magennis wrote in message
...


"Ron" wrote in message
...
Yamaha StagePas

Did I read somewhere that it's inadvisable to use metal bodied jacks on
the amplifier module outputs as the left and right grounds are at
differing potentials?

Or did I imagine that?

Ron(UK)



Yes, I said that.


But particularly metal right angle jacks that are almost bound to end in
disaster.


Gareth.



Assuming everyone has the eservice schema to hand. Where exactly is the
inverter in one ch of the 300 ? , I can see it in the 500 circuits

I've just noticed it written vertically at the amps . I thought the plug in
amps themselves were identical. Taking a closer look one is marked LF
6479e-01
and the other b instead of e, will have to look at the SM as otherwise
physically look the same. Just as well I marked where each came from as I
thiought they were interchangeable. But then as long as an "unmatched" pair
then would it matter which way round, assuming the ERR line worked correctly

I don't own a blink comparator, an app tacked onto a graphics package for
astronomy or anything?

Cannot see any extra transistor on either 300 amp.
Cannot see any different component
Cannot spy any trace swapping at Q7119 / 7120, where else to look for phase
swapping ? no other change of wiring seen or via pattern on the less
populated side.
Perhaps its under that white covering, only removed on the amp I've
repaired.

I also now have seen the change of arrow associated with the 300 output
jacks presumably indicating inversion also. You have to keep your wits about
you in this game for such bear traps

I don't quite understand how such designs ever make it to production.

Because its Yamaha? On some EMX I've disassembled to trace down an
immediate shut down problem I've been searching for 30 mins for a ground
connection between PSU/ PA/speaker ground to the mixer circuit ground.
Finally found it: one single M3 screw between the speakons connects the
power ground to the back plate, the backplate itself is connected to the
sheet metal shielding when assembled correctly and this is then
connected to mixer and preamp ground.
When the screw or the shielding comes loose, the PAs offset will grow
and shut down.