TU-8500 Working but no LED

[Brunes]

Dear All,
I built a TU 8500, its working but the LED doesn't come on. I check resisstor R58 and surrounding soldering and it looks good. LED will light up when I test continuity with a multimeter. Soldering looks good.
Should I just live with it, it sounds pretty good, volume works, gain adjuster works.

Thanks in advance

 

[rayma]

Is the LED connected backwards?
What is the DC voltage across the resistor connected to it?

 

[Brunes]

It's wired according to the diagram i.e I think its in the correct way.
DC voltage across resistor.. How is that measured? ( I checked R58 and its the correct resistor also).

 

[Mooly]

If I'm looking at the right circuit then pin 2 of the 4040 CMOS chip needs to be at logic 'low' (zero volts) to light the LED so check that.

(If the LED's in back to front it will have a highish voltage across it, correct way and a couple of volts)

 

[rayma]

Here is the LED polarity. The flat side goes to ground, and the other side goes to a positive voltage through a resistor.
https://en.wikipedia.org/wiki/File:LED,_5mm,_green_(en).svg

When you light it up with your DVM, which LED terminal is the red probe on, the flat one or the other one.

 

[vkung]

I am sure you install LED pcb incorrect
Check the manual how to install LED pcb
I assumed your LED polarity ok

 

[vkung]

The bottom of the LED pcb must touch the copper foil of the main Pcb
Pls check the manual

 

[Brunes]

The bottom of the LED pcb must touch the copper foil of the main Pcb

LED PCB is on top of main board... screwed down.

 

[Brunes]

It lights up with red probe on A and black on K and also with red probe on A and black probe on pin 2 of IC4. I also see r58 ressistance....

 

[vkung]

please check your soldering... If you can whattapps me around 1pm (PST time), I need to chat with you to resolve your issue

 

[Brunes]

I have no idea what i did. I must have assembled and re assembled many times. But nkw it works... thanks for all your healing vibes and support ! Bug in the system

 

[rayma]

Bad solder joint.

 

[vkung]

Red LED is not good .. too much current