Arfa Daily wrote:
"Puddin' Man" wrote in message
...
New here ...

Yamaha PSR-12, has maybe 72 keys, around 24 voicings, flexible-speed
percussion, canned tunes, etc. About 20 years old.

I turn it on lately, it works fine for 2-10 min., then freezes.
The little light that is supposed to come on for beat 1 (when
percussion accompaniment is running) locks on. That and the power led
are the only things functional.

The case has 2 halves. I workbench the thing turning the business
end (with keys and most PCB's) up 90 degrees to tinker, and it plays OK
for up to 3 hours (presumably lots longer). I figured the problem
has to do with either gravity or heat buildup, but I just left it
normally assembled and on for several hours and it didn't freeze up,
so maybe heat isn't the problem.

There are PCB's for power and switching, and 2 big PCB's presumably
for tone generation, special effects, etc. I tried some ribbon
cable connections: wouldn't budge. I'm afraid of breaking a
board or connector or ?.

It's gotta be repairable. I think. :-)

Any/all help/advice much appreciated.

Thx,
Puddin'


Stuff with micros locking up, often is a heat problem to do with the power
supply, especially if the item really is 20 years old, and more especially,
if it makes use of a switchmode power supply. As a first move, I would feel
inclined to pop a meter on the main 5v rail, and see where it's at, then
leave it on there, and see if it's any different, when the unit locks up. A
'scope on there wouldn't hurt as well. The rail should ideally be no lower
than about 4.85v and no higher than about 5.2v. The 'official' limits are a
little wider than that, but it won't have been designed to run outside of
the limits I've said. The rail should also be 'clean' with hash or ripple no
higher than say 20mV.

If there are any issues with voltage level or noise, look to caps and
resistors in the regulator circuit, for your trouble.

If the power supply turns out to be ok, the next place I would turn my
attention, is to the system control processor's clock crystal. Old xtals
sometimes get reluctant to oscillate, and will just stop after a short
while, in just the way you describe. You can often 'prove the point' by
taking the xtal out, and refitting it reveresed to its original orientation.

Finally, I have a dim recollection of a keyboard having a problem like this,
some years ago. As I recall, it too had a couple of large logic boards, and
ribbon style interconnects looping the boards and power supply together. The
'launch' level of the power supply was fine at 5v, but by the time it
reached the second board, having passed through tracks from one end of the
board to the other, and the in and out board connectors, it had dropped to
perhaps 4.8v, due no doubt to age-deterioration of the connector plating,
and the large current that all this logic draws on the older stuff. Anyway,
it was enough to cause the thing to keep locking up. Eventually, I decided
that there was no particular need for the supply to the furthest board to
loop through the nearest one, so I gave it its own heavy gauge wires
straight back to the power supply, which cleared up its problems completely.

Arfa


It`s just possible that a reset to factory settings might help[1].
There`s a list of Yamaha reset procedures here
http://www.yamaha-europe.com/yamaha_...ist/index.html

I dont see one for the PSR-12 but it`s possible that one of the other
PSR resets would work.

[1] It`s a long shot but it might work!

Ron(UK)