Seventh Circle Audio

Hi All,

I've been communicating with Tim on this but I thought I'd open it up to the forum.

I seem to have burned out(?) the pilot lamp on my chassis. I think it
might have been damaged while I was working on the front panel. I checked the connections and crimps and all of that looks fine. I opened up the lamp assembly and after a lot of work was able to expose the LED lamp inside. In doing so I destroyed the LED and resistor within so I have no way of now testing whether it was an internal connection issue (or determining the resistor value).

Now I'm basically looking for a replacement LED and resistor but wanted to run some numbers by everyone as I really can't figure out why it stopped working in the first place. The PS03 works fine otherwise. The +/-30V and 48V LEDs work and the unit powers the modules just fine. Across the pilot lamp header I'm reading roughly 68mA at -31.5V. This seems to be a lot higher than the 24v the lamp is rated for. Any thoughts on whether this is correct?

What values would you use for a replacement LED and resistor?

Thanks-
Stephen

It sounds like your measuring current through a short circuit at J1. 30v across the PS03's R19 will give about 64mA, at least until the resistor burns out. You can replace the LED with any other that will fit in the housing. The limiting resistor depends on the recommended current for the new LED. You can calculate it as follows:

R = ((30 - (LED forward voltage)) / (LED current in Amps) ) - 470

Use the closest standard 5% value.

For example, a red LED that needs 10mA of current will need a dropping resistor of 2410 ohms. 2.4K will work fine.

Thanks-- that seems to be working thus far.

I found a 1.8v 20mA and a 1k resistor at Radio Shack and they seem to be doing the job. The resistor gets a bit hot-- not smoking, but hot. I used a 1/4 watt. Should I move up to a 1/2 watt or is a bit of heat nothing to worry about?

And I'm not sure what you mean by short at J1. J1 is the header for the pilot lamp right? Are you suggesting that there is a wiring issue there causing a short? Or that it just shorted when I measured it?

I've been in the process of assembling my first unit (B16) but am having an issue with the power supply, similar to the above post.

When I first connected the wiring harness and panel lamp, plugged it in and turned it on, the panel lamp lit up (as did the three LEDs on the inside, +30V, -30V, +48V).

After doing some testing with the B16, I noticed that the panel lamp no longer lights up. I disconnected the B16, and the panel lamp still does not light. Looks like I blew it--no conductance across it. (Voltage across the panel lamp jumpers is 30.71V.)

I will follow the instructions for this post regarding what LED/resistor to replace it.

But my main question is: what could have caused this, and how to I ensure I don't do it again?

Thanks.

It could simply be so-called "infant mortality". We test all the panel lamps for at least 30 mins, but you may just have gotten a bad one.