Second opinions needed on a Luxman L-215 mod.

Hi everyone. I am one of those guys who really wanted to lean electronics properly but never managed to get by the basics in school. I therefor need a second opinion about some alternations I have made to a Luxman L-215.

I really like the look and the sound of this little amplifier but the one I managed to pick up had the same problem with overheated zener diode as many other have had. Just take a look at the attached images of the heated area around the original zener D112 (HZ20-3) and the back of the board. I also attached a part of the Luxman L-215 schematic (purple = 24V pilot lamp, yellow = zener diode D112, red = resistor R153 and green = capacitor C133)

I followed the advice at this page and replaced the blown 24V pilot lamp with a LED but there are a couple of things I am not 100% certain about.

I measured 23.9V, 112.4 mA before removing the zener and original resistor R153 (300-3) and 44.3V, 15.6 mA when the zener was removed and the resistor R153 (300Ω 3W) was replaced by a 2.7kΩ 2W resistor. That was before inserting the LED (rated 2V 16mA) so I guess there is about 42V over the capacitor C133 (47µF 35V). The guide I was following state:

“When the light bulbs are replaced by leds (that I prefer), the zenerdiode D112 is obsolete and can be removed, the 300 Ohm resistor R153, must be replaced by a 1,5 to 5,6 KOhm 2W type as on the photo, depending on the type leds you use, and then you have the correct power design.”

The zener D112 is gone and the resistor R153 replace by a 2.7kΩ 2W resistor but the text does not mention the capacitor C133 rated at 35V. My guess is that it mainly serve as a stabilizer for the pilot lamp and that it is not really needed for the LED (but this is me guessing). So I desoldered it and the amplifier seems to work perfect without it and the LED also seems unaffected by the removal of the capacitor C133, but I really don't know if its good or bad to keep it or remove it from the circuit.

So this is really my question, should I put the capacitor back in and what about the 42V in that case? Or should I keep it removed and not worry about it? Or should I do something different like add a new zener diode but I guess I then have to replace the 2.7kΩ 2W resistor and put another resistor in series with the LED…

Any second opinions are welcome.

Thanks in advance / Rob
 

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The capacitor is there to remove ripple, otherwise your LED will flicker somewhat. Replace with a 50V capacitor just to be safe.

The components mentioned have nothing to do with anything else in the amp - it's for the lamp only.

I recommend replacing the zener with a higher wattage part (1.3 W is good), and putting a new pilot lamp (24 V, ~ 20 - 50 mA) in. Original and best. I've done this and it works forever - with no heat issues.
 
First of all, thanks for your swift reply. :)

The capacitor is there to remove ripple, otherwise your LED will flicker somewhat. Replace with a 50V capacitor just to be safe.
That was my initial thought but the LED was fried when I did (I don't know why).

The components mentioned have nothing to do with anything else in the amp - it's for the lamp only.
That's what I thought, the LED does not flicker without the capacitor.

I recommend replacing the zener with a higher wattage part (1.3 W is good), and putting a new pilot lamp (24 V, ~ 20 - 50 mA) in. Original and best. I've done this and it works forever - with no heat issues.
That is what a friend also recommended me but this is where I run into problems (not having enough knowledge about electronics). The original zener diode is a HZ20-3 according to the PCB part list, the resistor 300Ω 3W and Vin around 46V. That gives me a needed zener diode power rating of 1.740W and 2.262W for the resistor. The original resistor is within spec and plugging the zener diode back in would drop the voltage over the capacitor so there should no longer be a need for upgrading it to 50V right? But I guess I would have to use a zener diode rated for at least 2W, am I right?

But I would actually prefer keeping the LED if possible but I don't know if the high voltage over the LED is bad in any way? And I guess the new 2.7kΩ resistor is the one generating heat right now instead of the zener...