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August 12, 2022, 08:21:57 PM

Author Topic: One LED not burning [resolved]  (Read 356 times)

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Offline Skipperrik

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One LED not burning [resolved]
« on: April 20, 2022, 12:52:34 PM »
The LED between the ground pin and A3 refuses to glow. Re-flowing the solder hasn't brought it to life.

Below are the voltage specs/values:

C4S
IA  150/147.7
IA  60-90/71.2
KregA  3-6/7.6
bKregA  150/147.7
IB  150/147.8
OB  60-90/39.2
KregB  3-6/4.0
bRegB  150/147.8

High Current 1
1A  190/193.7
OA  150/149.7
bA  0/0.4
IB  0/0.3
OB  90-110/76.5
bB  150/147.9

High Current 2
1A  190/198.7
OA  150/149.6
bA  0/0.4
IB  0/0.5
OB  90-110/95.6
bB  150/149.6

If you could help me figure this one out I would appreciate it!
« Last Edit: April 28, 2022, 10:05:13 AM by Paul Birkeland »

Offline Paul Birkeland

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Re: One LED not burning
« Reply #1 on: April 20, 2022, 12:58:09 PM »
Can you post build photos?

In attempting to reflow the solder joint on the LED itself, it's very likely to be damaged.  There are many other causes for that LED to not light up, so I wouldn't just focus in on the LED itself.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: One LED not burning
« Reply #2 on: April 20, 2022, 01:40:49 PM »
I'm afraid I haven't had much luck posting photos. Below is a link to the images on Dropbox but the preview says the links are "nofollow". It won't allow me to post a hyperlink either. What's the trick to uploading them?

https://www.dropbox.com/s/9rzrdhuo03ikwfn/IMG_4196.jpg?dl=0

https://www.dropbox.com/home/Crackatwoa?preview=IMG_4197.jpg

Offline Paul Birkeland

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Re: One LED not burning
« Reply #3 on: April 20, 2022, 01:55:03 PM »
Hit "Reply", hit "attachments and other options", there's a section that says "Attach:" and you can select your photos there.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: One LED not burning
« Reply #4 on: April 20, 2022, 02:10:08 PM »
The LED on the left is the problem. I also uploaded a photo of the board above the socket.

Offline Paul Birkeland

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Re: One LED not burning
« Reply #5 on: April 20, 2022, 02:23:01 PM »
Is A3 touching A4?

Again the LED itself isn't all that likely to be the issue, there are other faults that will cause the LED to not illuminate.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: One LED not burning
« Reply #6 on: April 20, 2022, 02:44:24 PM »
I checked the clearances around A3 and it wasn't touching either adjacent pin.

Offline Paul Birkeland

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Re: One LED not burning
« Reply #7 on: April 20, 2022, 02:45:24 PM »
Can you carefully measure the voltage on A3?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: One LED not burning
« Reply #8 on: April 20, 2022, 02:53:23 PM »
Will do, but here's another view of the pins.

Offline Paul Birkeland

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Re: One LED not burning
« Reply #9 on: April 20, 2022, 02:55:28 PM »
That LED looks to have a crack in it.  Generally a blown LED would produce a voltage of around 12-13V with the amp on, so if you see that you will need to replace that LED.  It's also important to reiterate that if an LED doesn't glow, there are loads of external causes that can produce that symptom, and the fragile LEDs don't handle a lot of extra heat from a soldering iron.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: One LED not burning
« Reply #10 on: April 20, 2022, 03:02:54 PM »
I checked the voltage at A3 with two meters. Both read 0 volts. Bad tube?

Offline Paul Birkeland

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Re: One LED not burning
« Reply #11 on: April 20, 2022, 03:06:39 PM »
No, the tube is operating correctly with the conditions it's being given.  With the amp off, what is the DC resistance between A3 and terminal 3 with and without the tube plugged in?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: One LED not burning
« Reply #12 on: April 20, 2022, 03:17:42 PM »
The resistance is 0 ohms both with the tube in and out.

Offline Paul Birkeland

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Re: One LED not burning
« Reply #13 on: April 20, 2022, 03:27:34 PM »
Yeah that's the problem, not the tube.  I would go ahead and pop off the LED going to A3 and see if that resistance changes.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: One LED not burning
« Reply #14 on: April 20, 2022, 03:34:39 PM »
Okay. That's major surgery. I'll have to work on it tomorrow and let you know the results.

Thanks for your help! I think we're getting close.