Hi Bob,
take care with switching power supplies
: many of them do not work properly when they are not connected to
a load. In some extreme cases, the power supply can even be
damaged as it can not regulate properly (the output capacitors can
be charged over their voltage limit)
So if you want to test the power supply
without connecting it to the synth main board, the best thing to
do is to put a dummy load on the main output (+5V in most cases).
Loading the power supply at 25 or 30% is enough most of the time
to allow the regulation to operate properly (so if the power
supply can deliver 1A on 5V for example, adding a 22 ohms/2W
resistor is enough to load the power supply. Take care however :
such a resistor becomes really hot !)
Benoit
Le 19/11/2020 à 15:59, Gunter Weeks via
groups.io a écrit?:
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Just a quick question, I replaced the
Caps when testing the 5 V side its reading 7V. Ive checked the
Switched side and there is a signal on the optical Isolator.
Ive pulled all the Transistors and
put them in a Tester and they all read ok
Question, Does there need to be a
load on the 5V line before the switching takes effect or Do I
need to look further?
REgards
Bob
On 13/11/2020 15:36, Grant B wrote:
On the main board, probably not. Some Yamaha things have +-18v
on the power supply that is further regulated to +-15 on the
main board, but those parts won't be under as much stress as the
PSU caps. You could take a look for leakage or swelling on those
if you like. I've never personally needed to replace those.
Anything that is suspect on the PSU should be changed. I've had
a couple of small signal resistors and ceramic caps on the PSU
that were eaten away. You might not know until you start the
removal and cleaning of the PSU.
GB
On 11/13/2020 7:22 AM, Gunter Weeks
via groups.io wrote:
Just
a quickie,
Ive ordered all the Power supply Caps.
Is it worth re-caping the main board It sounds fantastic No
humm etc..
Do I need to replace all the other type of Capacitors too?
Whilst Im doing this I thought I would re-cap my Original 1979
Korg MS20 Had it since new and this is starting to hum and
there are a few driy joints on the board which I thought I
would re-flow at the same time.
Regards
