Author Topic: LED Goes Green, But Not Red

December 02, 2023, 07:03:25 AM
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egelmett

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Everything passed the signal check...but during that test (#5), I noticed as the gain increased, the green would go out...the led dark, but the voltage increased as expected.

Any ideas?

December 02, 2023, 10:41:23 AM
Reply #1

JPK

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Something wrong around U3, R36...R46, D5...D11.
Check components value, direction and solder joints.
JPK

December 03, 2023, 06:54:05 AM
Reply #2

egelmett

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Something wrong around U3, R36...R46, D5...D11.
Check components value, direction and solder joints.
Thank you Jean-Pierre.


I did find D9 was reversed, but correcting it made no difference. I double-checked the value of all components in the vicinity of the U3, and D11 and R46...reflowed solder over everything there, but the LED would not turn red, just turn off. Lowering the gain made the LED green so, I can only conclude I must have damaged U3, or another component, in some way.

The preamp is functional (still - despite my rework, whew!), so, I'm just going to live with it the way it is.

On the next MP566 I'm building, waiting in the box, I will be more careful.

Thanks again!

Ed
« Last Edit: December 03, 2023, 07:00:23 AM by egelmett »

December 03, 2023, 08:56:53 AM
Reply #3

JPK

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With a strong input signal, when the LED should be full red, can you report the DC voltages on every pin of U3, against 0V?


(same principle for 14 pins)
JPK

December 06, 2023, 01:22:46 AM
Reply #4

egelmett

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Input was 1VAC 1kHz sine (from the Signal check):

1. -14.08
2. 13.57
3. 4.82
4. 15.27
5. -0.18
6. 4.82
7. -14.08
8. -8.6
9. 4.83
10. -0.05
11. -15.33
12. 4.83
13. 3.27
14. 14.19

December 06, 2023, 04:19:26 PM
Reply #5

JPK

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The issue seems to be between R45, R46, D11 or the LED.
Check the value, direction and solder joints.
Try shorting R46 with a wire. If the RED doesn't come, then the LED may be damaged.
JPK

December 06, 2023, 10:17:46 PM
Reply #6

egelmett

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Bad LED.

When I jumped R46, there was no change.

So, I was able to clip onto the bad LED legs (i.e. signal right off the PCB) and clip onto the LED from my second kit, and it lit RED as expected: when saturated.

Not sure if I damaged it, or bad from the factory.

How can I replace this?

Thank you again, Jean-Pierre!

December 07, 2023, 09:51:44 AM
Reply #7

JPK

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Contact us for a replacement.
Or get one more rapidly from Mouser or Digikey: WP937EGW

JPK

December 16, 2023, 11:29:56 PM
Reply #8

egelmett

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I was able to get a replacement from Digikey...all is working.

Thank you.

December 18, 2023, 06:19:53 PM
Reply #9

JPK

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