Korg SP250 Electric Keyboard - No Power - Fault Finding Advice needed

Thread Starter

Hecla_1

Joined Dec 5, 2017
6
Hi All,

First post.....looking forward to learning from the wealth of experience here.

I have a Korg SP250 keyboard that won't power up.

It has a seperate power supply (transformer) that I have tested and is outputting the 12 odd volts it requires, but the unit itself shows no signs of life.

I have opened it up for a look, specifically looking at the power stage PCB and see no obvious signs of issue (no burn marks or visibly blown caps).

The only other thing I have tested is the switch, which I bypassed to see if it was a faulty connection.....but no positive results.

Can some knowledgable person advise me on my next move?

Many thanks in advance!

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For context, I am an Audio Eng by trade, surface (day to day) knowledge of electronics and used to problem solving. I have fixed and built plenty of things in the past, yet lack deeper understanding and/or techniques of a regular electronics engineer. I am always willing to learn.
 

Thread Starter

Hecla_1

Joined Dec 5, 2017
6
Hiya,

Just checked two regulators as per the schematic....and they both appear healthy, outputting 5v and 9v as they should. (IC4 was 5v, IC3 was 9v)

So any further ideas would be much appreciated!
 

Alec_t

Joined Sep 17, 2013
11,137
Top right of the schematic it says
"* The amplifier is turned on by applying approximately 2.5 V or more to the STANDBYSW pin.
This is Pin5 on boards using the LA4708 and Pin4 on boards using the LA4628"
Are you getting that 2.5V?
 

Thread Starter

Hecla_1

Joined Dec 5, 2017
6
Thanks for this Alec_T

This is the IC you pointed out.... Just to check, am I right in saying they are counted 'left to right' from this image's angle? Many thanks! IMG_0599.jpg
 

Thread Starter

Hecla_1

Joined Dec 5, 2017
6
Black on 4 (or any other ground point).
Cool.

In looking at the schematic, I thought it would be Pin 4.

So I should see 2.5v (or close to) on the meter when I run the 12v power through the board.

I will report back. Thanks Alec_t
 
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