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previous: aris Crate GX212...I'm wondering if it's... -- 1087925475 View Thread

Re: Crate SS amp problem...?

6/22/2004 11:16 PM
Enzo
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Re: Crate SS amp problem...?
OK, it is the preamp. Now make sure both 15V rails are there. On the 8 leg dual op amps, the supplies are on pins 4 and 8. Pick a few chips scattered around the board and check. A line could have opened between sections of the board, but it is more likely that if there is power trouble, it is one of the supplies missing.  
 
Touch each chip with your finger. If any are hot they are bad. A bad chip can load down a power rail, so check for hot ICs first if one or both supplies are low. That your LED doesn't work makes me think missing supply.  
 
If the supplies are OK, then check the ICs. On the op amps, pins 1 and 7 are the output pins. Mostly there should not be any DC offset on those pins. If there is a couple volts or more, the IC is suspect. SOme ICs drive LEDs however, so in those cases we do expect DC. Making the lights go off and on can verify if that is what an IC is doing.  
 
After that, get the schematic, apply a sine wave to the input, and trace along until you find the cancer.

 
Replies:
aris I'm not really sure where to start ... -- 7/7/2004 2:09 PM