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Old 6th April 2007, 10:45 PM   #141
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Well I found a spare hour today.... and instead of concentrating on my new amp I thought I would bypass the input on my Lepai...why not....quick job I thougt...
Now bypassed and it has absolutely nothing there...pin drops....nothing!
This is very strange! I completely bypassed everything by running the RCA inputs through shielded wire to two of the pots ( giving me a balance control!) and then onto a set of Slimic caps (left over from a Charize mod)... then to a new pair of 20K input resistors to repace the 8K2's in there (must be because of some upstream series resistance on the old tone controls...

But when I power up there absolutely nothin...not a bean..the speakers are silent...not even a turn on thump?

I have completely bypassed the entire input section with no connections to the board what so ever... is there somethimng else I need to sever on the tracks other than the input channels?

There are no bad conections/solder joints as I have DMM'ed the lot and there is no logical reason for the lack of sound...what gives?
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Old 6th April 2007, 11:08 PM   #142
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Quote:
Originally posted by Lostcause
I completely bypassed everything by running the RCA inputs through shielded wire to two of the pots ( giving me a balance control!).......
I wonder if that opamp etc. is required if you are using the balance control? Maybe it will work without the balance control.
Were you able to separate the "Boss" control from the balance control without disrupting the signal flow?
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Old 6th April 2007, 11:49 PM   #143
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Quote:
Originally posted by Fin


I wonder if that opamp etc. is required if you are using the balance control? Maybe it will work without the balance control.
Were you able to separate the "Boss" control from the balance control without disrupting the signal flow?

hey fin,
When I say balance control, I just mean that I use one channel of each dual pot.
I also completely removed them from the board and rotated them to be isolated.
You can see from the pic that there is nothing untoward...wonder what happened? Pardon the Phone/camera quality...
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Old 6th April 2007, 11:58 PM   #144
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Is it possible that something in the old "bypassed" circuit is still connected.....and somehow draining the signal away?
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Old 7th April 2007, 12:06 AM   #145
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Quote:
Originally posted by Fin
Is it possible that something in the old "bypassed" circuit is still connected.....and somehow draining the signal away?

My thoughts exactly sir.... but where?

Is there something else connected on the power side that is upsetting the apple cart?

I don't know and it's too late for me to be bothered to be honest....time for bed


New day, new thoughts.....
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Old 7th April 2007, 01:22 AM   #146
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What does the brown wire do in the twisted pair that hops off the balance contols to the caps?

I see that the white wire comes from the wiper - good. And the brown wire from ground - OK, but where does it go?

Where does the signal go after the cap and resistor? Right to the sub board? Did you break the traces from the sub board to the main PCB?

Put a finger tip on the connections of the new input caps. Got hum?
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Old 7th April 2007, 07:54 AM   #147
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Hey Captain,
That brown wire is not connected at the other end, I just left the cat5 as a twisted pair and connect one end to ground to give it a semi shielded effect.... would have used the shielded wire but it got rather fiddly in there

The resistor is connected to the board where the other one was removed so it enters the signal path in exactly the same place but creates a break from the original traces.

No hum no nothing I'm afraid sir, even when you turn her on you don't even get the customary thump!... not even a click... but the power is definately there at the pins, I measured that as well.

It's really strange!
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Old 7th April 2007, 09:49 AM   #148
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Hmmmm.... OK.

I have a modded Lepai that refuses to run on one of my SMPS - a 15V job. The LED lights, but no sound at all.
Go back to the standard 12V SMPS and all is good.

Don't know why it's that way. Bad contact at the power plug? Electric voodoo? Don't know. I put it on the shelf for the moment - might have to bring it back down.
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Old 7th April 2007, 12:03 PM   #149
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I wonder if there is some kind of signal detection on the input that mutes it when there is nothing going through that elaborate input section? That's pretty much whats happening really, it seems like it is muted.
Now that I've completely bypassed the input it may be thinking there is no signal there?
Just a thought... I'll have a closer look at the mute pins later...
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Old 7th April 2007, 03:11 PM   #150
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Yes

There is a circuit that drives the mute to high, removed and permanently grounded...........

Now she sings again, quite a lot of DC offset but it sounds really good now. I'll put in the DC servo next week and that will just about do it!

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