Moog Music Forum

thealien666 wrote:Choose sockets with round legs (not the cheap flat ones).

Augat has been my choice for years. Very reliable IC sockets.

I just found some TL071CN will they do ?


are the CA3046 on ebay any good?

http://www.ebay.co.uk/itm/CA3046-Genera ... 2326e7006c


Thanks for all your support.!

I have one CA3046 .. so I swapped that out 1 at a time no change .. I also tried my TL071CN swap all 4 no different there.

You can maybe try to gently tap on the two ajustement trimpots at the top of the board. Maybe one of them is not making proper contact internally ? (dirty or oxidized wiper)

No Joy with the top pots..


Not should if it helps, but OSC is not tracking pitch at all ..

MC wrote:

grayedout wrote:OK that sounds like a good place to start .. will that change the sound in anyway

Does anyone know best place to buy CA3046 or 741 Op Amps..?

Try Mouser.com or Digikey.com

LF351 or TL071 best substitutes for 741 and it will improve the tuning stability.

CA3046 have been out of production, only direct substitution is NTE912 from Mouser.

funny there are lots of CA3046s on ebay and and one NTE912 , are they the wrong CS3046?

grayedout wrote:No Joy with the top pots..


Not should if it helps, but OSC is not tracking pitch at all ..

Are OSC 2 and 3 tracking the keyboard ?

thealien666 wrote:

grayedout wrote:No Joy with the top pots..


Not should if it helps, but OSC is not tracking pitch at all ..

Are OSC 2 and 3 tracking the keyboard ?

Yes they are working fine..

Then I can see only resistor 27 (cracked or desoldered) or IC1 or IC2 or IC3 being involved in the malfunction. These components all generate the pitch control voltage for pitch of VCO 1.

Or possibly bad contact inside trimpot R8 and/or R11.

thealien666 wrote:Then I can see only resistor 27 (cracked or desoldered) or IC1 or IC2 or IC3 being involved in the malfunction. These components all generate the pitch control voltage for pitch of VCO 1.

Or possibly bad contact inside trimpot R8 and/or R11.

if you have the time I have upload 2 pics below I can find IC1 and IC3 can't see IC2 ..


https://www.box.com/s/hoc9df2bmdpzh8nxsi4a

Any chance you could point out resistor 27 on this pic?
https://www.box.com/s/6ozfnzidp8mugspictn4

Click on the link below to see all parts numbers and their location.

http://www.fantasyjackpalance.com/fjp/s ... -below.gif

IC2 is shown as separate transistors on the schematics (but identified as IC2 and IC7 near each of them). Each SG3821 have 5 internal transistors. Two of which have one leg internally connected (emitter).

Just check with a multi meter and R27 reads only .600 but R80 and 129 read 2.200 ( i think they should all be the same)

can I replay with this?
http://uk.mouser.com/ProductDetail/IRC/ ... Wko4ywtOId

grayedout wrote:Just check with a multi meter and R27 reads only .600 but R80 and 129 read 2.200 ( i think they should all be the same)

???

R27, R80, R129 should all read 51.1 K Ohms (with only 1% tolerance) when measured separately and with the power off on the Mini (of course).

A few notes:

Moog published a bulletin recommending replacement of all SG3821s with CA3046 types.

Moog used 3046 (either CA3046 or LM3046) in many of their products.
Oberheim and Arp prefered the CA3086/LM3086.
I'm not exactly sure why. The 3046 apparently has slightly better specs.
There is also the LM3045J, a ceramic encased device with a US military number.
I keep all in stock, though they don't blow out all that often.
Often I'm replacing 3821s with 3046, but don't see too many go bad.

If the capacitor you have are coated in horizontal colored stripes they may be Mullard "tropical fish" caps.
While good caps when new, they have a habit over time of breaking off at one side or the other where a lead is located.
I tend to replace those with Cornell-Dublier (CDI) caps. One can get the same exact pin spacing and component size and they're made more sturdy than the old Mullards.

Before just replacing opamps, you might want to check if the opamp sending voltages to VCO1 is bad.
I suspect it may be a culprit and if so, pin 6 may have a very high voltage on it. I'm guessing 8 or more volts.
741s are still available all around and shouldn't be a problem obtaining.

As a hobbyist making repairs to equipment I own, or in projects, I have no liability to anyone else, and no one to blame but myself for the outcome. That said, I've bought and used 1468, 4013, 3080, 556 and 3046 chips from ebay sellers in the US, China, Hong Kong, Singapore and the Philippines with good results. Shipping is often included, and delivery times range between a few days and a month, with an average of about two weeks. Recently I ordered 50 2N3904 transistors from Singapore for $1.59, shipping included, and they arrived in 8 days. I needed one for a V-trig to S-trig conversion cable.