rhythm box removed from Hammond T 500

[Guest]

Hello fellow organ players!
Long time lurker here (a lover of my Farfisa bravo), with some rudimentary experience with electronics and some specific questions hopefully some of you could help me with.

I was recently given a rhythm unit, which has been taken out from a Hammond T 500.
(Link to Pictures included at the bottom of the post)
(I'm told the unit was working perfectly). I should mention I love the drums on my Farfisa, but am limited by space at the moment, hence me embarking on this quest.

What I'm looking to do, and I'm sure I've seen a few people having done so online over the years, is give this self contained rhythm box it's own power supply, and an audio output jack.

The back of the unit has a 15 pin (?) output-input, which I've not encountered before. (I've included a link to the image of the back of the unit).

I'd like to ask you nice folks

A) have any of you undertaken something like this before
And (apologies if this is an incredibly novice question) :
B) if a friend (very experienced in modifying electronics) and myself were to try and create this rhythm box to work as a standalone unit, what exactly would we need to purchase terms of electronics hardware to attach both the power input and audio output from the device?

In fact, any information about those 15-holed input-outputs would be much appreciated.

I have contacted an organ specialist who has said he could do it, but due to it taking a full two days, he's quoted an extremely high price. (I'm assuming this is down to it being arduous rather than any hardware being expensive.)

Anyway, any and all input and information would be hugely appreciated, and I look forward to hearing what you have to say!

FF

Pin input/output
http://imgur.com/NxZ8hqM

Front
http://imgur.com/hmd6pfI

[handyczech]

I would suggest looking for a T-500 service manual on ebay or elsewhere.
The power supply was inside the organ, and there was also some interactive switching with the manuals, pedal, and expression pedal. This is a bigger project than you might imagine, even if electro-savvy, and especially without a schematic. Brendon on this forum is a T-mod expert. He can advise better if he sees this post. Earlier units from t-400 back through the L-200 and rhythm drawer were easier to use as stand-alone because they were built somewhat more generically by a Japanese supplier and just wired in.

[RogerRabbit]

T500 service manual here https://archive.org/details/HammondO...al-T-500Series look in download options for the PDF version (2 parts), part 2 has the Rhythm 111 schematics

[Brendon Wright]

Hiya Matt!

I did a bit of fiddling with mine but in the end it didn't work out how I wanted to use it.
This is a pretty complex little bit of kit.

Here's the brief history:
To start with I turned it into a unit separate from the organ... but for use it still plugged back into the signal chain of the organ as designed.
Eventually I decided I'd never use the "something in the air tonight" rhythm I kept it for and trimmed it up so it just provided a bit of "thump" when I played pedals.
I've still got it in a box in that form if anyone ever needs reference, but I couldn't tell you how I narrowed it down to the necessary bits!
My "scientific method" is just trial and error, not actual electronic knowledge.

There's a board inside the organ called the "auto accompaniment" board which died on me once again and I decided to do away with it once and for all. (It had been smashed into about 6 bits by the drum machine FALLING onto it ten years back or so. Never been the same since...)
I figured out how to get the pedals and lower manual working without this board but I never figured out how to get the pedal thumps back: something in this board seemed to be essential to the whole gate-triggering thing.

That may or may not matter for straight rhythms.
What I CAN tell you is this:

The big fat 15 pin socket at the back of the rhythm unit is detailed on page 5-15, it shows the numbering of pins but doesn't give a clear understanding of WHICH way up the plug is.
Once the plug layout is properly established, page 5-20 tells you which pins do what:

The far right list the one we want: "Plug J5 rhythm input/output".

Pin1 requires +25VDC
Pin 2 is to be grounded.
Pin 3 goes to the organ volume pedal, If I remember rightly you don't need to do anything with this.
Pins 4 to 10 go to the "Auto Accompaniment board". We'll need to decipher each one's purpose by looking at the pins at the Auto-Accomp end of the wires (Page 5-12). It's quite a tough board to fathom without electronic knowhow.
pin 11 is grounded at the Rhythm end but not at the other end in order to give shielding to the wire from pin 12.
Pin 12. this goes to a resistor behind the tabs, I'd have to look at my photos to find out what the OTHER end of the resistor goes to.
13 - nuffink.
14 shield wire for wire running from pin 15
pin 15: this runs to a resistor and a white wire somewhere behind the tabs. Most likely detailed on the organ block diagram on page 5-2.

SO, all of this is going to need a good bit of exploration. Is anyone able to chime in and trace these wires?
Work's a bit crazy here at the moment and my organ forum visits are fairly intermittent!

[Brendon Wright]

Phew, thanks to the holiday I'm almost ready to sink into this problem again.
I don't know enough to actually solve the job, but by working out what the pins on the accompaniment board supply the drum unit it may help someone get to the solution.