Speedball LED

[StevePL]

I have a small issue with my Speedball.
The Crack is 1.0 2016 vintage.
The LED at position D1 on the A side of the board does not illuminate.
Here are the voltage check for the Small Circuit Board
OA 66.7V
IA 172V
B-A/B 0V
1B 171.9V
OB 78.4V

Here are the voltage checks for the Large Circuit Board
OA 102.4V
OB 96V
G 0V
B+ 173.5V

All the voltage checks on the crack before the Speedball were within operating range.

 

[fullheadofnothing]

Did you do the voltage check on the small board before installing the large board?

 

[StevePL]

Did you do the voltage check on the small board before installing the large board?

Yes. A&B sides were pretty much identical and and the LED in question illuminated the same as the other three LEDs. The problem arose when I connected the Large Circuit Board.

 

[Paul Birkeland]

Can you verify that this is the case in a dark room?  Your voltages look spot on, and if one of the C4S LEDs wasn't illuminating, that shouldn't be the case.

 

[StevePL]

Can you verify that this is the case in a dark room?  Your voltages look spot on, and if one of the C4S LEDs wasn't illuminating, that shouldn't be the case.

Yes, in a very dark room. I know it's odd as the voltages are all close enough. I've been listening to it for quiet a while like this and it's a wonderful amp paired with the HD600s.
I had a knee surgery recently so I'm killing time by finding projects to keep myself busy. This was one of them.

 

[Paul Birkeland]

It's actually possible to measure the DC voltage across the LED that's dark while the amp is running.  , with the black probe on the banded end and the red probe on the unbanded end.

 

[StevePL]

It's actually possible to measure the DC voltage across the LED that's dark while the amp is running.  , with the black probe on the banded end and the red probe on the unbanded end.

The three bright LEDs are 1.5V The one dim LED is 1.3V

 

[Paul Birkeland]

I'd flip the little PC board over and look for incomplete solder joints or solder bridges, especially around the PN2907.  You can also post a photo of the bottom of your board here and we can check it over.

 

[StevePL]

I'd flip the little PC board over and look for incomplete solder joints or solder bridges, especially around the PN2907.  You can also post a photo of the bottom of your board here and we can check it over.

I reflowed the solder joints, no difference in the voltage readings. I also checked the large PC board on the A channel and it all looked good (to me).

 

[Paul Birkeland]

I would reflow all of the joints in the red circles.

 

[StevePL]

I would reflow all of the joints in the red circles.

Done and still the same voltage readings.

 

[Paul Birkeland]

Did your Speedball kit hang around long before you installed it? Do you live in a humid climate? (or was the unbuilt kit stored in a humid area if applicable)

 

[StevePL]

It's been installed for over a year. It's always had this problem. As I said earlier I'm on sick leave so I'm trying to sort out things that aren't quiet right around my home. The amp sounds fine. I've just always know that LED isn't properly illuminated.

I'm in sunny Burbank,CA so humidity isn't so much of an issue here.

 

[Paul Birkeland]

Yeah, you could certainly replace it and see what happens! Seeing 1.3V across that LED is really odd.  Usually if there is a problem, they open up.

 

[StevePL]

Yeah, you could certainly replace it and see what happens! Seeing 1.3V across that LED is really odd.  Usually if there is a problem, they open up.

I've replaced that LED with no change in the voltage reading.
I think I'm just going to leave it well enough alone and continue enjoying the amp and ignore the dim LED. With my hearing the amp sounds pretty dang good as it is.

 

[Paul Birkeland]

If replacing the LED gave you the same results, I'd replace the PN2907 next.

 

[Paul Joppa]

Might be worth checking the R1 value while you are at it.