Out of spec voltages and an LED is not lit [resolved]

[Hudson]

Hi,

I have just finished putting together the kit. It passed the resistance check, however it did not pass the voltage check.

The top LED (the one connecting to A8 and center pin) fails to illuminate.
Finally, the 2 big white resistors get pretty hot. Is this normal behavior? Are these bleeder resistors?

Voltage readouts (VDC):
1: 150
2: 165
3: 0
4: 165
5: 82
6: 0
7: 150
8: 0
9: 106
10: 0

Thanks,
Hudson Green

EDIT: The voltage on A8 is around 13VDC. This is much higher than on A3, which is around 1.5VDC. Does this signify that the LED needs to be replaced? I assume the LED is supposed to act sort of like a pull down resistor. If so, what is the part number for it? Is it available on Mouser?

[Paul Birkeland]

The solder joint at A5 doesn't look to be captured by solder, and this would also cause only one side of the 12AU7 to illuminate.

Typically we expect about 100V across each 3K resistor, and this produces about 3W of dissipation in a 10W rated part.  Because your terminal 1 voltage is so high, one of your 3K resistors is dissipating almost 8W instead of 3W. 

The bleeder resistor for the power supply is the little 270K/1W carbon film resistor.

[Hudson]

Hi Paul,

I added a bit more solder to it and reflowed the joint, however this did not fix the LED, and the voltages are still where they were.

[Paul Birkeland]

Can you carefully measure the voltage at A8?

[Hudson]

Yep. A8 is still 13VDC. Does this indicate that the LED is dead if it is supposed to act as a pull down resistor of sorts?

[Paul Joppa]

Seems likely - or else, it's not successfully soldered. You can measure at the leads (not the terminal) for continuity or resistance, swapping test leads to test both polarities. The LEDs are somewhat fragile, so Bottlehead offers a 5-pack for $7.50.

[Paul Birkeland]

13V usually means the LED is open (or extremely loose, tug on each lead with your needlenose pliers to be sure they don't pop out).  Usually this happens from too much heat exposure during soldering.  If you have a Speedball kit, you can rob an LED from it to replace that one and get your kit chugging or order replacements from the mothership.
https://bottlehead.com/product/hlmp-6000-leds-prod/

[Hudson]

I used one of the LEDs from the Speedball and the voltages are now correct. Thank you Paul!