korg sdd2000 resets when input volume peaks

[rothers]

ive got a korg sdd2000 that cpu resets when the audio level goes into the red , i have done the usual replaced most of the caps, and checked psu levels which all look fine. If i disconnect vu leds delay does not reset using basic functions ,but resets when i use the sampling function ,i can manually put a high input on the reset pin on the cpu which stops the cpu resetting but not ideal, anyone come across this on korg sdd's?

[nosaj]

ive got a korg sdd2000 that cpu resets when the audio level goes into the red , i have done the usual replaced most of the caps, and checked psu levels which all look fine. If i disconnect vu leds delay does not reset using basic functions ,but resets when i use the sampling function ,i can manually put a high input on the reset pin on the cpu which stops the cpu resetting but not ideal, anyone come across this on korg sdd's?

Did you replace the caps because of this issue or did this issue happen after you replaced all the caps?
service manualhttps://elsonidodeu2.files.wordpress...ice-manual.pdf

nosaj

[g1]

Lower left of pg.11 in schematic posted by nosaj. IC24, pin1, is 5VDC holding up when it resets? Also check for AC voltage ripple on that pin when it resets.

[rothers]

i replaced ic24 and q23 during my fault finding, it was resetting like this before i changed all the caps. Just cant find the component thats dropping the voltage..to cause ic24 to reset. It all works ok if i bypass ic24 with a high5v dc on the cpu reset pin.

[mozwell]

IC24 replaced, Q23 replaced....
Are + & -15V supplies ok when input signal goes into the red
Is the +5V supply ok when the input signal goes into the red
Maybe when the red led turns on, it momentarily pulls down the 5V supply causing a reset.... problem in IC12 or leaky cap ?

The leds run from IC12 & the 5V supply (top right of page 10), the reset line around IC24 & Q23 does not connect to this at all...
I would check all the electrolytic caps around IC12, especially the small 10u ones. These can cause problems when they are old. I'm not sure how many of them there are on the board, but maybe its worth while replacing them all .... and see if this helps maybe also the 47u electrolytics and any other small value electrolytics

You could also try changing C75 to 100u & maybe R90 to 1k

If there are any tantalum caps, replace these with new ones, and replace any electrolytic caps up to 47u

But i would check the power supplies first !

[rothers]

thanks will have a look at that, ive changed all 47uf and 10uf caps but no tants, voltages look fine ,not checked the 15v when it brownouts as i was concentrating on the 5v that feeds ic24, ive even put a new 7805 in for the 5 volts!

[rothers]

i also was going to remove ic12 altogether as it only drives the leds!

[g1]

You can replace IC24 and the 5V regulator that feeds it, but you still have to monitor pin1 of IC24 and see if the 5V is holding up when it resets.
This is a quite critical.

[rothers]

fixed!!!
hi came back to this and finally fixed it. It was a faulty diode in the 5 v bridge rectifier , as the leds lit with audio in an ac ripple appeared on the 5v dc , enough to trip the cpu reset. should've spotted that earlier before i replaced all caps,etc!!! least its been fully refurbished....

[g1]

Yep, that's the ripple I meant in post #3.
Glad to hear you got it working right.

[rothers]

yes thanks for the tip , that's what spured me on to look for ac in 5 volts , tracked it all way back to the bridge rectifier , the big cap must gave been smoothing it until it went under load