CGS75 VCS build questions

[russma]

There are three or four places on the PCB where there are a pair of holes and just a straight white line between them (on the silkscreen side). These holes have pads on the underside.

Am I supposed to jumper these with thin solid wire? The photo on Ken's site shows this, but it's an old PCB (the red one), and I'm not sure if it still applies.

I didn't see anything in the build notes about it.

(This is the first of what may be multiple questions)

[decaying.sine]

Take a look at the parts overlay. The jumper in the middle, edge of the board supplies positive VDC to pin 8 on the TL072. Without the jumper the IC wouldn't be connected to the positive rail. If your PCB version has a connection from + rail to pin 8 on this chip, and still has the jumper, then the jumper is likely not needed. Looks like pin 4 is connected to the negative rail without a jumper as far as I can see on the revision posted online.

The other jumper connects ground. If that is connected or your revision then you should be good to go.

I'll take a look at mine a little later to see if the new revision PCBs are connected.

[andrewF]

Yes install a piece of wire, usually called a link.
Expect to see a couple on most PCBs

[decaying.sine]

Just peaked. I have the CGS75 rev 1.0 PCB. It looks like the jumpers are needed for the reasons above. I think the third jumper is also needed as well as it provides negative rail source to pin 11 of TL074.

Take all this with a grain of salt. I don't know what the hell I am really talking about. Maybe Luka, neandrewthal, or peake or another more experienced builder can chime in.

[decaying.sine]

or andrew!

bob's yer uncle!

[Luka]

links = necessary

though sometimes on doublesided boards it looks like they need links but is actually a trace which is weaving from side to side

[russma]

Thanks folks.

[russma]

Ok, links are soldered in, and now I'm on to the wiring, so some basic wiring questions:

Pots:
Facing the pot shaft, terminals are from left-to-right, clockwise, wiper and counterclockwise; correct?

Switches:
Should the middle terminal be connected to ground? I assume not.

Sockets (jacks):
Facing the terminals, (the back of the socket), with the "angled" corner top right, which is the signal lug? Do I need to connect the ground lugs?

Power:
There are pads on the PCB for providing "0 volts" and "+volts" (two each); what do I connect these to?

[decaying.sine]

Hey IB,
Check out this thread at EM: http://www.electro-music.com/forum/topic-36504.html

Here is a nice wiring pic for the pots. from j.dilisio in the same thread.



I attached the switchcraft datasheet (actually I'll PM it to you), which should answer your jack questions. You can connect the ground lug and then link them to a ground source on the PCB (or other place). Tip spring terminal is on the left is angled portion is upper right.

Power: these go to the rise and fall rates. check the wiring diagram I attached.

Horse: Here is a horse... This horse is amazing.

[russma]

awesome. Thanks very much Brian!

[russma]

I'm embarrassingly switch ignorant:

Do I need to connect the center lug of the switches to ground?

The switches that came with the parts kit have three terminals; is this normal for SPST switches, or are these SPDT switches?

[Luka]

they work the same, they just have another lug to switch to instead of being off
to ensure i wired the switches the correct way i cut off the un-needed lug

[russma]

to clarify:

these switches have no center position, but they have three lugs. Should I connect the two wires from the PCB to the two outer lugs and ignore the center lug?

[Luka]

so they are on-on
the middle lug is connected to either side depending on the throw
connect middle and one side

[russma]

Not surprisingly, my build isn't working. No blue smoke, but when I plug it in, my Q960 sequencer stops working!

Adopting pugix's method, I checked the power pins for resistance and get well over 1K on both pairs.

Not sure about the switch wiring, as stated above.

Using the typical switchcraft jacks, the lug on the angled edge should be grounded, correct? I had it that way to begin with, then removed the ground connection, but it made no difference.

[russma]

so they are on-on
the middle lug is connected to either side depending on the throw
connect middle and one side

excellent. Thanks Luka, I'll report back.

[russma]

Switches are now wired correctly, but no change in the problem.

I've read a lot about the transistor pinouts being wrong; not sure how to test for this?

[terrafractyl]

I just went through this slightly painful procedure... actually i only realised after desoldering all the transistors that I could have done it with them all still on the pcb.... ah well.
Also I found a lot of methods for testing the polarity of transistors and they nearly all involved building a circuit with LED's and resistors.... then i found this method, which was 10x easier.... please someone correct me If I'm wrong.

Okay so check the data sheet for the transistors to determine which pins 'Should' be the base, collector and emmiter.
For my 2n3906's + 2n3904's this was both the same, With the flat part of the transistor facing upwards the pins were Emitter - Base - Collector from left to right.

So with a DMM set to diode mode you can test them. For PNP (2n3906) you need to place the black lead of the DMM on the base and then place the red lead on first the Emmiter and then the Collector. The base - collector should read a very slightly smaller number than the base - Emitter.

( On most of mine is was something like b-c = 0.665 b-e = 0.674 )

For the NPN (2n3904) you just need to swap the black and the red leads of your DMM whilst testing.

Hope you get it working... I'm still trying to find my problem

[jarvis]

has anyone moded theirs with an EOA output? can you just tap pin 4 of the lm3900 or do i need to put something else in there?

[russma]

...Okay so check the data sheet for the transistors to determine which pins 'Should' be the base, collector...

Thanks very much terrafractyl! Using your method, I found that on one of the 3904's, the BC and BE readings are exactly the same. This is the transistor nearest the power input.

Any idea what this means?

[russma]

I should add that all five other transistors read as expected.

[russma]

Looking at the schematic, that transistor is listed as a BC547. I assume a 3904 is an acceptable susbstute, yeah?

[Adam-V]

Should be OK but I think the pins on the 2n3904 are the reverse of the BC547. You'll probably need to mount it backwards.

Cheers,
Adam-V

[J3RK]

The angled side of the jack is ground btw. I just ran a bare copper wire through rows of them (giving CV and audio related jacks separate wiring to the PCB.)

If I'm not mistaken (and I can check later or tomorrow morning, my transistor read the same way (same both ways.)

Any further progress?

One thing of note, on the first one I did, I didn't pay close attention to the two entries following the RRW and FRW in the pot wiring. (meaning I grouned, but didn't connect CW to +VE.) Silly mistake, but thought I'd mention it just in case.

[terrafractyl]

wow... i didnt see that! The BOM + the pcb says 2n3904

but the data sheet for a BC547 has the opposite pin out arrangement to the 2n3904... maybe this is the problem, i'm going to test this right now!

Nice work eagle eyes!


As for both pins reading the same I'm not sure. maybe defective? could it have gotten warm? I read that the temperature of the transistor can affect the test