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Old 20th February 2010, 05:50 AM   #1
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Default Anybody familiar with current limiting on Technics amp modules?

Trying to fix an AV amp, SU-G86, probably from the '90s. It prematurely current limits at a couple watts into 8 ohms. It should do over 100 watts. Can't find any shorts, nothing burned or odd looking, all the caps measure ok for C and D, all the resistors, diodes and transistors also measure ok. The amp modules have a line labeled Overload, shared between two modules. I assume either can declare an overload situation, pull the line and trip the relay. The relay gets tripped sooner with a load, but even without a load it trips at about 20Vpp out. Does anybody have experience with Technics power modules (RSN3305-P), or access to data sheets?

Thanks,
Conrad
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Old 20th February 2010, 12:42 PM   #2
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i will presume that ofset readings are correct and also elctrolytics arround the protection circuit are replaced ....

it is obvious that a bit of ofset will alert the protection circuit

As we speak i will try to dig a schematic

regards sakis
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Old 20th February 2010, 12:46 PM   #3
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ok i have the schematic ....please e mail me so i can give it to you its kinda big to post here
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Old 20th February 2010, 05:24 PM   #4
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Thanks Sakis, email sent. I'm hoping this is some simple leakage problem, but I'm not going to change all the caps without more of a clue as to what area might be the trouble. All the caps have been measured in-circuit and they show correct value and low D. That doesn't mean one or more couldn't be leaky, but I want to isolate the trouble before pulling parts on a guess. My fear is that something is amiss within one of the power modules, and at $70 each the repair wouldn't be worth it.

Best,
Conrad
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Old 20th February 2010, 08:52 PM   #5
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I got this thing is a somewhat disassembled state. I reassembled it with all new hardware, and now it's working. I hate it when that happens. Either there's a bad solder joint, cracked trace or the screw-down connection to the board grounds wasn't good. I think I'll beat on it a while and see if any glitches show up.

CH
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