Roland PSD-120 schematic?

[Lizard King]

I'm trying to build a power supply for my Roland rack modules.  I put together a 5V, 2A circuit but it doesn't seem to turn the modules on.  Does anyone know where I can find a schematic or circuit design for the PDS-120 so I can try to see what Roland is doing special.

Thanks!

[bluebunny]

The PSD-120 appears to be straightforward centre-negative like our pedals:



Have you got the polarity right?  I don't see what "special" thing they could be doing... 

[Lizard King]

Yep....polarity right.  I thought I had 2A worth of current capacity but maybe I'm a tad shy, although I assume they usually over build their power supplies.

I had to add a 1000uF cap and diode between the lm7812 and ground to get my 9V circuit to duplicate the psa-120 & get my homemade unit to work with a DD-500.  Roland does some whacky stuff.

[duck_arse]

fiver-point-seven volts, champ. you need a 1N4148 between the regulator ground pin and the supply ground, to jack up the voltage by ~~600mV, so the circuit can then eat 600mV.

got your whacky stuff right here.

[Lizard King]

Lol....I tried that.....after it didn't work I looked again (with magnifying glass) and realized I had picked up a 7809....D'OH!  Fortunately the 7.8V didn't blow up the module....but it didn't turn it on either.  ;-(

Had to order in some 7805's.....that'll be my next attempt: using the real voltage.  I figured since the Roland supply is rated at 2A and 78's are generally rated at 1.5A I'd either double up the 7805 or heat sink it.

Thanks!

[duck_arse]

double up AND heatsink it. have you canvassed all the options, like a bigger reg, or a series pass transistor, like that?

[Lizard King]

double up AND heatsink it. have you canvassed all the options, like a bigger reg, or a series pass transistor, like that?

No I haven't.  I'm kind of a one trick poney, LOL.  78 series or 317 series regs are about all I know.

I have a PSD-120...I'd pull it apart but I doubt I could learn much by looking at their components. 

[Lizard King]

So I got a 12V 2A power supply....took a 7805 with a 4108 diode to ground 1000uF cap to plus 220uF cap to ground - pretty much like a PSA-120 only 9V.....DOES NOT POWER UP THE Roland Demora.  I have a psd-120 (same polarity as my effort) - powers up fine.

Any suggestions

[bluebunny]

Did you measure both PSUs?  Volts is volts.  Roland don't have special physics just for them.

[Lizard King]

Mine is 5.65V, Roland is 5.8V.  I can't believe .15V would make a difference.

[bluebunny]

Me neither.   

[Lizard King]

I had an issue du-kicating the PSA-120 - but someone posted a schematic and they were using a 1000uF cap where I was only using a 100uF cap.  Once I swapped caps I could drive a DD-500 with my power supply.

I'm stumped with this one.

[duck_arse]

voltages. the output voltage of the jacked-up reg, loaded and un-loaded. maybe even the voltage into that reg, loaded and un-loaded. measure the current drawn (at 5V6 or whatever it is) by the pedal/s when powered by the correct supply.