mdz

why would someone drop a 909 to the floor while it´s running?
i got no idea either, but recently it happened to a friend. his TR threw a few sparks before the main fuse of his studio blew and gone was the bumm-bumm :(

not to rain on roland´s designing skills (and given the fact usually you don´t throw a 909 on the floor) but the position of the original PSU board is somehow dangerous for flying 909s; since the AC solder pads directly face the bottom plate any impact in that area possibly short-circuits the main AC power. you better put some cardboard or isolating rubber between the PSU board and the bottom plate - well, it´s best not to throw 909s on the floor too ;)

unfortunatelly in our case the the shorted AC line was led to the voiceboard PCB through the metal battery compartment, blasting a few semiconductors and GND traces there. see the picture for details (note the PSU has been exchanged on the image already):

certainly the main transformer was blown after this accident. as the 909 had to be returned into its productivity environment asap (sic!) there was no time to organize a suitable transformer so i had to exchange the PSU completely…

USE AT YOUR OWN RISK! the following procedure is pretty dangerous. if you don´t know what you´re doing you may cause irreparable damage to your gear or yourself. see the spark damage pics above, you don´t want anything like this occuring to your 909 or your body!

we need three power lines in the 909: +15V, -15V and +5V. the available PSU (meanwell) was pretty big: 159×97x37 mm. i was afraid it was too big but finally found a way to mount it safely inside.

a fourth powerline is the reset circuit. the original roland design derives the reset circuit from the input of its 5V regulator. the reset line must go high shortly after power-on and not drop below 4.7V or the TR will reboot. i think today´s switching PSUs are pretty stable so i took the reset line from the 5V outlet instead and rebuilt the stabilizing reset circuit from the schematics - just discarding the zener diode.

allright. first step is to get out the old PSU and the AC-input jack (we need that space for the new PSU tray). two holes in the backplane are to be drilled:

now comes the bitch: a new AC connector hole needs to be drilled and filed. thanks a lot the TR-909 is rock solid made of steel ;) one hour later you´re ready to install the AC input to the power switch and the new PSU. i designed an L-shaped tray to be hooked into three screws on the backplane and bolt down on the voice board mounting screws (with small stand-offs in between). it´s best to test PSU and reset circuit voltages before connecting to the 909 boards. when done it should look like this:

the power connections are pretty self-explanatory: +15V, -15V, +5V, the reset circuit mentioned above. all the ground connections come to one common ground, we ditch the analog/digital ground separation.

that´s it. another 909 is back to life and thanks to nowaday´s switching power supplies it´s accepting any voltage from 100-250V now. bumm-bumm is back in town. too bad i had to return it to its owner ;)

This entry was posted on Thursday, April 22nd, 2010 at 11:35 am and is filed under blog, diy, recording & gear. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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