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 Post subject: Re: What does this do?
PostPosted: Thu Aug 10, 2017 10:04 am 
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Sheep

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georgehifi wrote:

If I just pull off CN8 connector purple, no oscillations even with all PCM1704's, I/V, gic filter and output buffers still powered.

Cheers George


You have a problem with an LCD, most likely with an inverter


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 Post subject: Re: What does this do?
PostPosted: Thu Aug 10, 2017 10:19 am 
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Cow
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Extreme_Boky wrote:
georgehifi wrote:

If I just pull off CN8 connector purple, no oscillations even with all PCM1704's, I/V, gic filter and output buffers still powered.

Cheers George


You have a problem with an LCD, most likely with an inverter


LCD?? liquid crystal display?

Cheers George


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 Post subject: Re: What does this do?
PostPosted: Thu Aug 10, 2017 9:18 pm 
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Cow
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Terry.
Disconnected, 1 and 2, from connector CN8, supply for FAC (VFD1 display).

Now no display, but dam it, oscillation is still present.

Cheers George

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 Post subject: Re: What does this do?
PostPosted: Fri Aug 11, 2017 1:55 am 
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Just measured the output voltages of the three 7805 regs, U29 at 5.02v U31 at 5.02v But U5 is 4.85V.

This U5 reg is the 5vd3 feed to the laser, is it possible that the (working fine) laser is causing this .15v drop, and can it be the cause of the oscillation?

Cheers George


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 Post subject: Re: What does this do?
PostPosted: Fri Aug 11, 2017 4:16 am 
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Cow
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Changed U5 7805 and it's 1000uf cap, for 1500uF, voltage has come up to 4.95V other 7805's are all 5.02v
But the oscillation is still there.

Is it possible that while the laser reads and plays everything, that it can still be faulty and give out this malignant oscillation?

What sort of RF frequency do lasers emit?

Cheers George

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 Post subject: Re: What does this do?
PostPosted: Tue Sep 26, 2017 2:50 pm 
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Cow
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What does this do?
- Ehm. My first thought, despite the weirdly drawn schematics was "gyrator thingie". Well, reading further thru the GIC explanations on the internet proved me, somewhat, right.
Why am i writing all this? Well, to thank you for an educational moment!


Ah. May i ask?
1. It appears to me as a 3rd order low-pass, 2nd order GIC + passive stage afterwards.
2. Given 1, and the use of NE5532, why haven't they did the passive first, and then GIC?
I always strive to filter passively before going thru OpAmps.

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