MC-505 LED Replace

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MC-505 LED Replace

Postby lotsanobs » 01:56, 2 January 2017

I will be replacing some dead tactile switches for my MC-505 pads.
On key pad 14, pad works but LED light isn't showing, so definitely a dead LED there.

Anyone know the spec for replacement LED's for the MC-505 pads ?
The Roland LED part # is: slr-56vct32 (for pads 1 - 16 & TAP)

Would like to replace original reds with new BLUE LED's.
Thanks.
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Re: MC-505 LED Replace

Postby genesis92 » 15:44, 26 January 2017

they seems to be regular 5mm through hole leds so you can buy 5mm blue leds but the voltage drop of blue leds is higher than red, yellow and old green (570nm) leds.
sometimes that can cause problem to the electronic but if I have free time and find the service manual with schematic I can check this point.
http://www.digikey.com/product-detail/e ... ND/2337245
the specs of the original led is:
Color Red
Lens Color Red
Lens Transparency Clear
Millicandela Rating 25mcd
Lens Style/Size Round with Domed Top, 5.00mm
Voltage - Forward (Vf) (Typ) 2V
Current - Test 10mA
Viewing Angle 40°
Mounting Type Through Hole
Wavelength - Dominant 630nm

I've checked the schematic it's ok but beware the old leds have less light efficiency than the newest ones so I think you will have more ( 100 times! ) light output with new leds.
to give you an idea the original led in the TR-505 is 25mcd @ 40° @10mA. a blue newest one will be more 2000->5000mcd @ 40° @ 20mA!!!
the original led forward voltage is 2v and is drived by high and low side transistors with 47 ohms limiting resistor.
the DC current is near (5-(2.2v+0.6*2))/47 = 34mA but less because it's scanned
with a blue one you will get (5-(3+0.6*2))/47 = 17mA in DC but less by the scanning rate
if you are blinded by the new leds you will have to increase led limiting resistors value.
you must have some skill in electronics and double check anode/cothod orientation on the PCB
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Re: MC-505 LED Replace

Postby ZipSnipe » 13:54, 12 April 2017

Good find and good info
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