SX 980 protection circuit concern

creeve

Active Member
Happy Memorial Day All! I have an sx 980 that I’m in the process of bringing back from the dead. It’s was a real basket case. Anyway after I rebuilt the amp boards with new caps and trim pots I fired it up and it had over 2 volts of dc offset on one of the channels BUT it came out of protect. I was able to dial the dc offset in although it’s very jumpy. So why is the protect circuit not protecting??? 2 volts would have damaged speakers if they were connected.
 
2-3V is about right to trip DC protection. Did you wind it up can check when the protection kicks on to verify?

2-3VDC isn't going to cause any damage to your speakers for a short time.
 
The IC should be set for a voltage of +-1.8vdc max.
Check R5 and 6 for proper 75k ohm value.
A poorly operating chip?
 
The IC should be set for a voltage of +-1.8vdc max.
Check R5 and 6 for proper 75k ohm value.
A poorly operating chip?
Yeah definitely went way past that. I will check the resistors. Only other thing I can think of is maybe because there was no load connected but that really doesn’t make sense either.
 
Yeah definitely went way past that. I will check the resistors. Only other thing I can think of is maybe because there was no load connected but that really doesn’t make sense either.
Hi Creeve ,
Just curious as to what you found on the resistors ? I’m having a issue as well my sx-980 won’t come out of protection mode either... I definitely will be checking R5 &R6 when I get home .
 
If you confirm that the DC offset and the idle current are OK but still in protection check the overcurrent transistors, Q8, on each channel. 2SC869s are known troublemakers and will cause the amp not to come out of protection. Correct idle current will let you know there's no overcurrent condition. If you see any light blue Sanyo capacitors while you're in there get rid of them also.

Craig
 
If you confirm that the DC offset and the idle current are OK but still in protection check the overcurrent transistors, Q8, on each channel. 2SC869s are known troublemakers and will cause the amp not to come out of protection. Correct idle current will let you know there's no overcurrent condition. If you see any light blue Sanyo capacitors while you're in there get rid of them also.

Craig
Thanks for your reply!
 
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