Replacing TL074 opamp in Soundstream CA 3.0

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#42
Perry Babin said:
It's better if you repair these cards in place. If you have to remove them for some reason and you have a soldering iron with a variable temperature, use ChipQuik. It will help protect the pads on both boards.

ChipQuik is also good for removing the driver transistors. Most people damage the board trying to remove them.
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I would have left them in, but there are electrolytic caps standing in the way on both sides of the cards. I could not get my iron and solder sucker in there without risking making contact with the caps. Either way, removing the cards were fairly easy. I replaced the MPSA18, MPSA92, and the 1n914 diodes along with the KSA1381/KSC3503 drivers. I need to start looking at the opamp on the main board because I still have 200mV and 16.5V at the speaker output. If the opamp checks out, then I guess I'll think about replacing the 2SC3067 again. I've already pulled all the TIP102/107 off the board and they all test good. This has been the most stubborn amp I've worked on. These amps are not that complicated - it shouldn't be this difficult to repair it.
 
#44
Perry Babin said:
You don't need to use much. A 1" length would likely be more than you'd need to remove a board like this. 1/2" may have been enough.

I know of no other supplier of that type of product.
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I'm quite happy with the brand but wondered if there was a cheaper place to buy it other than eBay..

this doesn't seam bad value for money and the more you buy the price goes down 🙂

CHIPQUIK CHIP QUIK REMOVAL ALLOY 4.5 FEET | eBay
 
#46
How much current flow (2mA total?) is there suppose to be through the differential pair formed by the 2SC3067? I'd like to check this by either measuring the voltage drop across R213, R214 or R230 on the preamp card. Thanks guys.

Rgs, JLH
 
#47
JLH said:
I've been still working my way through this amp. I traced one of the problems to a defective 2SA1479 driver transistor on the preamp card. I couldn't find any, so I substituted a KSA1381 for the 2SA1479. I also substituted a KSC3503 for the 2SC3789. Looking at the data sheets the KSA1381/KSC3503 are dead ringers for the obsoleted 2SA1479/2SC3789.
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I noticed the originals are "d" sub type for a specified hfe 60-120. I can only locate a "d" of one and "e" (hfe=100-200) of the other at mouser. Would this really be a problem or nothing to worry about? I've got a 2sc3789 that appears to be leaking, tests ok out of the circuit, but hooked up, I have almost rail voltage instead of ~-0.9V shown here.
 
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#48
durwood said:
I noticed the originals are "d" sub type for a specified hfe 60-120. I can only locate a "d" of one and "e" (hfe=100-200) of the other at mouser. Would this really be a problem or nothing to worry about? I've got a 2sc3789 that appears to be leaking, tests ok out of the circuit, but hooked up, I have almost rail voltage instead of ~-0.9V shown here.
Click to expand...

You should be fine. It really doesn't make much difference.
 
#49
JLH said:
How much current flow (2mA total?) is there suppose to be through the differential pair formed by the 2SC3067? I'd like to check this by either measuring the voltage drop across R213, R214 or R230 on the preamp card. Thanks guys.

Rgs, JLH
Click to expand...

Just bumping this to see if anyone knows the answer to the above quoted question. Thanks guys!
 
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