Quick help needed with LED in 5150 & 5150II

[jutsin]

Hi guys,

I've replaced the normal red/green LED's in my 5150's and a friends with some bright blue ones (from radioshack. link= Rectangular High-Brightness Blue LED Lamp - RadioShack.com) and they always burn out. Some more quickly than others, but it always happens. Do I need to add a resistor in to keep them alive or something? thanks for the help!

[loudthud]

The first 5150 schematic I downloaded didn't have the power supply. The second was for the 50W combo version. When I looked at the Radio Shack page, the technical specifications were blank. So this is just a wild guess. The Power and Status LEDs are run from the AC side of the transformer, about 18V RMS. My guess is that they are getting too much reverse voltage. Install a diode, 1N914, 1N4152 or 1N4007 anode (non-banded end) to ground.

[Jazz P Bass]

It appears that Peavey uses a 1.5K series resistor on each LED.
You may want to go a tad higher on the resistance.
Try a 2.2K.
If you go too high, the LED will be dim (& last forever)

[jutsin]

Thanks for all the help! I'll give those suggestions a shot and see if is remedied.

[Gingertube]

I would say loudthud is "on the money".
The LEDS operate on one side of the Centre Tapped AC winding which is used for the +/-25V raw supply - that means that it is probably around 18 to 20Volts AC. The 1K5 will give 13mA peak but half wave so equivalent of 13 x 0.63 to bring it to average and x 0.5 to account for half wave - so that is the same as running the LEDS at about 4 to 5 mA. That should be fine.
What is NOT fine is that you are exceeding the LED's reverse breakdown voltage (typicaly about 6 volts) put a diode in series with the LED as loudthud suggests. That way the added diode handles the reverse voltage and protects the LED.
If the LEDs are too bright you could increase those 1K5 resistors.
Cheers,
Ian