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Old 22nd November 2012, 12:25 PM   #1001
AndrewT is offline AndrewT  Scotland
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I would expect offset<5mVdc from start up and not have to wait for days.
regards Andrew T.
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Old 22nd November 2012, 12:42 PM   #1002
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Location: Milan, Italy
Originally Posted by bcmbob View Post
Dario answered them but somehow the notice showed but the post didn't. Here is a try.
I've deleted my message because I thought we were talking about the FE...

Some answers still apply, some not, like the one on C102/C202 or on DC offset, as already pointed out by Andrew.
ClaveFremen "Bailando Salsa en el Sietch"
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Old 22nd November 2012, 12:46 PM   #1003
bcmbob is offline bcmbob  United States
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You are too quick at the trigger. Wondered what had happened to your reply/post.
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Old 22nd November 2012, 12:59 PM   #1004
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Thanks all, and I will be using the Lightbulb tester as per the instructions on Decibel Dungeon.
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Old 26th November 2012, 03:39 PM   #1005
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OK, I finally wired up the MyRef C (original version from UDaily), and went through all of the checks with the light bulb tester, however some problems, the chief of which is no sound.
  1. Rails measure fine at 35 V dc
  2. OpAmps measure at a little over 12V dc
  3. LM3886 has 35V dc at the pins
  4. DC Offset is around 3mVdc

The strange thing, apart from no sound, is the power LED's. Only one channel had the LED shine when I switched on, the other channel's LED didn't shine. However, when I switched off the amp, after a few seconds the channel who's LED didn't shine, lit up briefly.

Now both channels LED's do not shine, although that is my fault as my probe slipped on the LM318 when measure for voltage. There was no smoke, but the one working LED went out. However, when I power the amp off, after a few seconds both LED's shine briefly and then go out.

From reading the threads it looks like the LM318's are the culprits, although I don't understand the LED behaviour.

All my LM3886's are insulated from the heatsink, including the shoulder spacer for the screw.

I've checked the polarity of all the capacitors and they are fine, however I don't hear the relays kicking in anymore. One certainly did (the channel who's LED originally worked), but after I'd had a slip with the probe, that relay stopped clicking in.

Comments on my issues, and symptons?
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Old 26th November 2012, 05:56 PM   #1006
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The rails look ok, and the output DC offset is fine (this should be measured between the output and PGND). You probably need to re-check the protection relay circuit - values, shorts, opens.

Another quick sanity check is to swap the LM318 with a TL071. If it works with the slower TL071, then it's probably a stability issue with the LM318.
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Old 26th November 2012, 06:29 PM   #1007
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Thanks Linuxguru.

Values I can easily check, however how would I go about checking for shorts and opens, apart from visually checking it?

I'm confident my soldering is good, so I doubt it's a dry joint, however you never know, so that leaves shorts.

Oh, and what particuar TL071 would you recommend?

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Old 30th November 2012, 05:59 PM   #1008
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Hi all

Some partial success; I now have one channel working, however the original channel that would not work, still will not work.

I've replaced the LM318's with new ones, and I've also tried a TL071, but it refuses to work.

I'm thinking that it's now more likely to be an issue with the relay/related fuse values, however some expert advice would be appreciated.


Edit: I just turned the amp on without any Op amp in the channel that refuses to work, and and I now get the power LED lighting up, whereas before (with the op amp in place), the power LED would not come on.
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Old 30th November 2012, 10:15 PM   #1009
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hi westers,

youll want to check the feedback comp caps (15,22,150,220pf valued caps) i had the same problem as you when i had burned one of those caps.
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Old 1st December 2012, 11:58 AM   #1010
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How can you tell if those capacitors are ok? They look fine (solder joints are shiny, no obvious signs of burning), and the values are correct.
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