First, some info:
On IC30(gate Array) the relevant pins are:
Pin 56: Bass Drum
Pin 57: Snare Drum
Pin 59:Low Toms
Pin 60:Mid Toms
Pin 61:High Toms
Pin 62:High Hat
Pin 63:Rimshot/Cowbell
Pin64:Handclap/Tamborine
The problem sounds like you may have severed one or more traces that run undewr the gate array. To fix this all you need to do is to solder 3 jumper cables. They are:
From pin 13(IC29) to pin 9(IC33),
From pin 10(IC40) to pin 3(IC34), and
From pin 12(IC29) to pin 3(IC34).
Those 3 jumpers will re-attatch all the leads that need to run underneath the Gate Array(IC 30).
Below is a letter that I sent to a few guys who had written me for help on the TR-707 mods. I hope it helps. let me know how it goes:
Jon-I used this basic 555 oscillator circuit:
http://hobby_elec.piclist.com/e_ckt5.htm
I replaced Resistor A with a 1k and Resistor B with a 100k pot. You
will run a wire from pin 3 on each of your oscillator circuits to
each of the individual pins(56,57, 59-64) on the Gate Array (IC30).
The Oscillator bank that I made has 10 oscillators because I pitched
the Ride and the Crash Cymbals as well. More on that later.
In each Oscillator circuit I replaced the Capacitor with a different
value. You will have to experiment with this as personal taste
dictates how low you want the pitch to go. I built a single test
oscillator first,with a socket that I could trade out different Caps
so I could hear which I liked best.Here is a list of what I ended up
with:
Pin 64 - Hand Clap/ Tamborine (.0027 Cap)
Pin 63 - Rimshot/Cowbell (.0022 Cap)
Pin 62 - High Hat (.005 Cap)
Pin 61 - High Tom (.005 Cap)
Pin 60 - Mid Tom (.005 Cap)
Pin 59 - Low Tom (.005 Cap)
Pin 57 - Snare (.001 Cap)
Pin 56 - Bass Drum (.001 Cap)
I used Pin 10 on IC 23 for the Ride (.005 Cap) and Pin 10 on IC18 for
the Crash (.0033 Cap). On the Oscillator circuit for the Crash I also
changed Resistor 1 to a 12k. This seems to work fine for the first 707
I did, but with the second one I'm getting different results(on the
Crash). I still have to tweak that one some more.
Unlike the pins on the Gate Array, the pins for the Ride & Crash (on
IC23 & IC18) do not need to be detatched from the board. I tried them
unattatched and the results weren't as good.
I attatched all the +5V power together and ran it to Pin 28 of IC35.
The Grounds (-) all go to Pin 14 of IC35.
Let me know if you have any questions. Also, The decay mods that I did
are simple and well worth doing.
Max
And a follow up letter:
You don't need to make a break in the tracks leading to the IC 30
pins, but you DO need to unattatch the pins from the board. This mod
won't work unless the pins are unattatched. from their original
oscillation.
I turned a tiny screwdriver under the pins while heating the solder
holding them to the circuit board.(see attatched drawing) BE VERY
CAREFUL because if the pin breaks off from the IC you will lose
whatever voice that pin is permanently. DON'T let the soldering iron
linger too long on the pin or it will fry the IC.
I ran red wires from the pins down to a junction mounted along the
edge of the board (so that the IC30 pins wouldn't be yanked around by
repeated opening and closing of the enclosure-see photo) and then used
the junction to solder the oscillator outputs to.
If you want an overide to use the stock sounds you'll have to have a
seperate overide switch for each voice. A SPDT toggle with the center
lug attatched to the IC pin, left lug to your oscilator, right lug to
the circuit board where you unattatched the pin from(or somewhere
along a path that connects to it). I attatched schematics to help you
with
this.
By the way, if you can't get the pins up and end up cutting the leads
on the board somehow, a quick fix is this: Solder jumper wires from
pin 13(IC29) to pin 9(IC33), pin 10(IC40) to pin 3(IC34), and pin 12
(IC29) to pin 3(IC34). Those 3 jumpers will re-attatch all the leads
that need to run underneath the Gate Array(IC 30).
If you are going to put oscillation on the Ride & Crash, I used pin 10
of IC23 (ride) and pin 10 of IC18(Crash). I found that it's better if
you don't unattatch the pins from the board. On the Crash oscillator I
used a .0033 capacitor and a 12k resistor on it's 100k pot, because it
makes some wierd sound at the top of the dial so I tried to lower the
headroom.
I haven't tried the BD Decay, but I'll bet it's similar to the others
if you study the schematics. Try a keyword search on the 707 yahoo
user's group. I'll bet it's there.
Instructions for the OPEN-HAT & CLOSED-HAT Decay can be found here:
http://www.smack-dynamik.com/smack_dynamik/viewtopic.php
p=20243&sid=fa4ec810397f4fe74bc5f31c773033a4
RIDE & CRASH DECAY can be found here:
http://launch.groups.yahoo.com/group/tr-707/message/35
I powered all my oscillators together from IC35: + goes to pin 28, -
goes to pin 14.
I used different capacitors on the different oscillators to give them
the ranges I wanted for each voice. I also had to add resistors to
some of the pots to add a ceiling to the range. I had to experiment
because on each 707/727 they were slightly different.
Let me know if any of this is unclear, or you can't open the
attatchments or you need more info. At any rate let me know how it
goes.
Cheers,
Max
To: tr-707@yahoogroups.com
From: gabrieldannunzio@...
Date: Mon, 10 May 2010 09:27:56 +0000
Subject: [tr-707] Pitch mod problems
Hi,
I desolder pins 59 to 64 of the gate array, without cuting the tracks
I made 6 oscilletors using a 40106, instead of six NE555...
Than I solder the outputs of the 40106 oscs to the pins .
BUT... when I move the potenciometer of one oscilletor to control the pitch of an instrument (e.g. Clap)I affect pitch of other instruments (e.g. toms) ... Why it is so
furthermore. .. I desoder pins from 59 to 64 but I can't control BD and SN pitch!!! Why
Thank you in advance for your kindly reply...