Urei LA4 silver face issue RESOLVED !
- Thread starter innercityman
- Start date
Help Support GroupDIY Audio Forum:
..neither LED or LDR are known to fail, I'd look for errors beyond the protocells...
/Jakob E.
/Jakob E.
could be side chain related, but I would expect open side chain to command max compression, of course open circuit from side chain to turn on the opto gain reduction could result in no compression.
JR
JR
innercityman
Well-known member
Thanks guys for your advices.
I've desoldered the photo cells and tested them. Their Ohm values varie to the light exposure so they are not faulty. I tested the leds with my multimeter and both light up. So Jakob was right, the issue doesn't come from the photo cells or leds.
As the LDR were unsoldered, I fired up the unit and sent signal into it to see if the leds light up. In any threshold or ratio positions, none of them light up.
Do you think it could be a faulty op amp ? As you still can find NOS 4136N ICs on eBay for a cheap price, I said to myself that I it's worth a try to buy a pair and replace the threshold/ratio and side chain related ones. The original ones aren't socketed but directly soldered on PCB, so I decided to put the new ones on sockets.
I've desoldered the photo cells and tested them. Their Ohm values varie to the light exposure so they are not faulty. I tested the leds with my multimeter and both light up. So Jakob was right, the issue doesn't come from the photo cells or leds.
As the LDR were unsoldered, I fired up the unit and sent signal into it to see if the leds light up. In any threshold or ratio positions, none of them light up.
Do you think it could be a faulty op amp ? As you still can find NOS 4136N ICs on eBay for a cheap price, I said to myself that I it's worth a try to buy a pair and replace the threshold/ratio and side chain related ones. The original ones aren't socketed but directly soldered on PCB, so I decided to put the new ones on sockets.
Bo Deadly
Well-known member
You need an oscilloscope. But a DMM might be enough. Put a 100Hz signal through it and trace through the circuit testing for AC signal. Start with the 10K pot and then the inputs of each amp of IC3 and see that signal is present. Just be careful to ground yourself so that you don't zap something with static electricity.
If it is an op amp like IC3, that looks like a funky pin out and 36V? Check your supply to see if it's really +-18V. RC4136 is only +-15V max so you can't really to put that into a +-18V supply. You could try it but if it explodes, then it won't work.
If it is an op amp like IC3, that looks like a funky pin out and 36V? Check your supply to see if it's really +-18V. RC4136 is only +-15V max so you can't really to put that into a +-18V supply. You could try it but if it explodes, then it won't work.
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innercityman
Well-known member
I solved my issue. IC3 RC4136 side chain related op amp was faulty. Changed it and it works like it use to. I'd like to thank Jakob, JohnRoberts and squarewave for bringing me into investigate in this direction.
Love this forum, I learn everyday !
Love this forum, I learn everyday !
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