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Old 2nd January 2013, 05:42 AM   #721
PMA is offline PMA  Europe
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Quote:
Originally Posted by chiily View Post
I've disconnected the shunt reg and the trace is present on the +18V, -18V and GND pins coming out of the shunt. It is also still present on the GND and OUT pins...is this RFI I'm seeing?

I've read back through the thread and noticed that there was the posting of another trace, some oscillation and also -5V on pin 6 of the servo...I'm seeing that too (though only with the shunt connected!!).
Most probably it is not RFI only. The amplitude is too high, voltage swing about 70mVp-p, ripples with approx. 5MHz repetitive frequency. What happens if you turn off the mains power for the power supply? Do the oscillations disappear?
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Old 2nd January 2013, 05:44 AM   #722
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Quote:
Originally Posted by chiily View Post
I've disconnected the shunt reg and the trace is present on the +18V, -18V and GND pins coming out of the shunt. It is also still present on the GND and OUT pins...is this RFI I'm seeing?

I've read back through the thread and noticed that there was the posting of another trace, some oscillation and also -5V on pin 6 of the servo...I'm seeing that too (though only with the shunt connected!!).

I'm running about 37V into the shunt.
If the signal is also visible on GND then there is something in the environment that induces this signal in the connection leads of the scope.
You need to check the scope connections and the mains connections.
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Old 2nd January 2013, 06:07 AM   #723
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Quote:
Originally Posted by FdW View Post
If the signal is also visible on GND then there is something in the environment that induces this signal in the connection leads of the scope.
You need to check the scope connections and the mains connections.
If there is an HF oscillation, the ground may become easily contaminated as well. He has too switch of the power with everything else connected same. He also should seek for equipment with switched mode power supplies connected to the same AC line. Anyway, the plot he posted is to regular to be a product of SMPS, these products usually measure as bursts of high frequency damped impulses with some lower repetition frequency. And he complains for hot transistors.
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Last edited by PMA; 2nd January 2013 at 06:10 AM.
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Old 2nd January 2013, 06:30 AM   #724
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Quote:
Originally Posted by hesener View Post
thats not a big problem, it is the servo compensating the offset of the amplifier. 5V is high but still within the capabilities of the opamp. I would suggest to let it settle another two weeks turned ON and see what happens, eventually this voltage will come down or at least become stable.
Thank you for your answer, so this high voltage will come down after a while.
I will check again after some time.

The 2,2 V across the ext. RIAA is no problem also? Both boards.

My 0,0000 V at the input looks strange, as I said the trimmer has no function to the input. Both boards.

Should I change the trimmers?

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Old 2nd January 2013, 08:06 AM   #725
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Quote:
Originally Posted by chiily View Post
I've disconnected the shunt reg and the trace is present on the +18V, -18V and GND pins coming out of the shunt. It is also still present on the GND and OUT pins...is this RFI I'm seeing?

I've read back through the thread and noticed that there was the posting of another trace, some oscillation and also -5V on pin 6 of the servo...I'm seeing that too (though only with the shunt connected!!).

I'm running about 37V into the shunt.
Can you give me the voltages at TP101,102,103 and 104 and also TP201,202,203 and 204.

Running the shunts from 37V is a bit much, try to run them from 30V or slightly less.

Remove C105 and C205 and see if the oscillations/noise are/is gone.
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Old 2nd January 2013, 10:07 AM   #726
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Quote:
Originally Posted by FdW View Post
Can you give me the voltages at TP101,102,103 and 104 and also TP201,202,203 and 204.

Running the shunts from 37V is a bit much, try to run them from 30V or slightly less.
Yes good advice
either get different trafo or ad same more CRC (Capacitor Resistor Capacitor about 20 Homs)

With 36 V and R2 sinks (bit biffier than ones I had with goodies bag) temperature was up to 70 C
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Old 2nd January 2013, 12:17 PM   #727
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Thank you for your help so far...

Quote:
Originally Posted by FdW View Post
Can you give me the voltages at TP101,102,103 and 104 and also TP201,202,203 and 204.
37V into shunt, amp not connected.

TP201 -18.07
TP202 -19.45
TP203 -22.06
TP204 -0.533

TP101 18.06
TP102 19.66
TP103 22.16
TP104 0.552

Quote:
Originally Posted by FdW View Post
Running the shunts from 37V is a bit much, try to run them from 30V or slightly less.
I don't have a Traffo 18V handy. The next one down I have is only 15v, which isn't enough. I did try the 15V one but half the LEDs under the heatsink didn't illuminate correctly.

At 37V in the heatsink does get a little toasty I've only run the board for periods of about 15mins so far.

Quote:
Originally Posted by FdW View Post
Remove C105 and C205 and see if the oscillations/noise are/is gone
Okay, not tried this yet.
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Old 2nd January 2013, 12:27 PM   #728
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I let some magic smoke out today.

Click the image to open in full size.

The two bottom LED's on the left hand edge of the board burnt out along with the 337 that you can see with its die exposed.

Was this likely caused by a failure in one of these 3 components or is it more likely a failure or a short on one of the components on the heatsink?
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Old 2nd January 2013, 12:43 PM   #729
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Did you have the 337 under the heat sink and its top was very close too or hitting the sink ?
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Old 2nd January 2013, 01:10 PM   #730
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Under normal operating conditions the 337 will carry 2mA's of current, that will be 2mA * 24V (if the supply is 42V) = 48mW (about/max). The only reason for this failure is a broken power transistor (the output voltage is 18V so the shunt was operating as expected). You should replace Q101, Q102, Q103 and Q104 (I'm almost sure that Q101 or Q103 is broken). Check for shorts between Q101, Q103 and the heatsink (that could be the source of the damaged transistors).
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