[sdiy] EFM VCO4e troubles...

[Jay Schwichtenberg]

There aren't any PCB mods for the 4E, there are for the 4D which is what I
thought the original post was about.

I went and checked out my 4E. Every thing pretty much followed the
schematics. With EFM stuff there will be a lot of differences between the
BOM (Bill Of Materials or parts list) and the schematic. Usually the
schematic is right.

Here are the changes I made:

 R36 in the PWM part I changed to 56K from 82K.

I put a 50K trim pot in for R37 to get a better sine wave out.

On U4 pin 1 I put a resistor to ground. I think 5K-10K will work. The
comparitor has an open collector output and needs to be pulled up with a
resistor.

There are three things that I can think of that might cause problems:

1) There are places for 2 - R14s, the expo tempco resistor. If you are not
using a tempco resistor put a 1K resistor in the resistor slot marked R14.
If you are using the tempco put it under the CA3046 - U2. DO NOT DO BOTH,
ONLY DO ONE!

2) FETS. There are a number of different fets that can be used as the
switches that short the cap. Problem is not all of these have the same pin
out. So check the fet pin out you are using vs the way the board was layed
out.

3) The sync fet must have it's input grounded when not in use. This is done
with the jack on the schematic. If you leave it floating it may trigger or
stay on all the time.

Another thing I saw looking at the information doc for the card and my
boards is that they are slightly different. Look at the placement of the FM
IN pin. On my boards it is more towards the center of the board. In the doc
it is closer to the CA3046 - U2.

Good Luck!
Jay S.

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of nN AAt e e
> Sent: Sunday, February 20, 2005 3:37 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] EFM VCO4e troubles...
>
>
> ok, i know Julian posted about this about this a few weeks ago... but
> now it's my turn to have trouble. this is what i'm getting
> confused with on
> my first of two VCO4e modules:
>
>     on the parts list, caps #3 to 8 are listed, but the schem has
> just C 3 -
> 7, and the board has spots for C 1 - 7... it also want's c4 to be a
> polyester cap, but everything that was included with either kit was all
> ceramic... i'm just getting a little confused.
>
>     i was also wondering why the parts list has R39,45,20,44 but
> only has a
> quantity of 2... i would assume the resistors not included are part of the
> optional heater, but one of the locations is nowhere near it?
>
>     Jay S mentioned that the VCO4e will work with all the
> documented mods...
> but i haven't been able to find
> anything about fixes on the EFM message board, and the email archive link
> doesn't work... [and no, nothing obvious in the VCO4e pdf either]... if
> anyone has ANY docs that include fixes, i would greatly, greatly,
> appreciate
> copies of them.
>
>     so unless there is something pretty obvious that i'm looking
> over, i guess i've hit a dead end. thanks for any help... i can't wait to
> finish these up and try them out.
>
> - nathan