On Thu, 25 Jan 2007 09:54:35 -0000, "Mungo \"Two Sheds\" Toadfoot"
put finger to keyboard and composed:

Hi all.

My Roland E-500 has a problem: after ~5 minutes of being switched on it will
turn itself off and immediately switch back on again. It will then do this
every few minutes, or after a longer period of time, or sometimes not at all
and will work normally. There is nothing happening physically to the
keyboard to trigger a restart and the mains lead is good.

It has an internal switching power supply board and a seperate power
amplifier board with a small relay on it which clicks when the power goes
on, and when the keyboard restarts itself.

I found a discoloured and cracked 220ohm resistor on the power board and
replaced it, even though it was still testing at 200ohms, but this has made
no difference. I've also re-soldered any joints which looked suspect.

One other possible symptom is that the main transformer on the power board
hisses. The sound changes if I push on the transformer itself, or on the
board. There are two large capacitors near the transformer, one of which has
a small bulge on the top, which can be pushed back down easily, but shows no
sign of leaking, nor do any of the other caps.

Any thoughts?

I can put some pictures of the power board on the internet if it would help.
It has big "proper" components on it :-)

Simon.

I don't think the largest caps are your most likely culprits. Instead
I think that the one near R12 is probably the root cause of your
problems. As a general rule I always check the smaller electrolytics
on the primary side of switchmode PSUs (eg the one near R2) as these
often go high ESR. But as others have advised, change all the caps on
the supply secondary for good measure.

- Franc Zabkar
--
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