Melcore PCBs

If you're looking for pcb's, Jeff sells em at his shop.... the gar1731

http://classicapi.com/catalog/index.php?cPath=71_72

-d

No, I have 20 PCBs from Bauman lying around here. 

Just want to make sure that I stuff them correctly.

What version of the PCB do you have?

There are lots of confusion because of different designations between schematics
and PCBs.

One version of the PCB is faulty but easy to mod.

i have one little board too but cant find any docs again!
Thanks.

Again, what version?

Best,

Anders

I have this version, which seems to be the corrected one:

Yes, this one is correct.
There are several PCBs around and one of them is faulty, its marked with the code 04/18
(not to confuse with 04/20 witch is correct)

Instead of BD135/136 you can use BD139/140.
R4 = 39k the lowest one on your pic could be 44k (or 39k+4.7k), works for me
Connect C2 (coming from BD136/140) directly to -IN (base of Q2)
Important! dont forget the double diode (D2), its the lowest one on your picture.

To get the 1731 to work better with a API312 type circuit you can add a 100-120pF
cap between OUT and -IN.

If you want, I can put a BOM together with the components/values that worked for me.

Hope this helps,

Anders

Sredna said:

There are several PCBs around and one of them is faulty, its marked with the code 04/18
(not to confuse with 04/20 witch is correct)

Click to expand...

There is no such code on my 1731 PCBs. It just says "rev1". But the traces are the same as in the image.

A BOM would be very nice.

Where did you get the 6 pins from?

Ok, Ill put something together.

Does your PCBs got component designations (R1, D2, Q3) or values(360R, 4148)
or just silhouettes on them?

I ask because the designations differ between the PCBs and schematics.

Sredna said:

To get the 1731 to work better with a API312 type circuit you can add a 100-120pF
cap between out and in.

Click to expand...

Do you mean between out and -in?  That would basically add to your feedback cap. I think people were doing that before the "double diode" thing was "discovered." Once I stuck 2 diodes in series in mine (ages ago), all oscillation went away.

Sredna said:

Does your PCBs got component designations (R1, D2, Q3) or values(360R, 4148)
or just silhouettes on them?

Click to expand...

Component designations.

Thanks mitsos, corrected to "-IN".

Concidering the 100-120pF cap, Fabio (Baumann) recommended it in this post:
http://www.groupdiy.com/index.php?topic=246.msg137455#msg137455
It was after the double diode was discussed but I dont know if Fabio was aware of
this issue.

Im sorry, I dont want to contribute to the great confusion in this matter so I suggest
not to use an additional 100-120pF cap between OUT and -IN if the 1731 works ok.  

Here's the BOM for the 1731 REV1 PCB:
http://www.twin-x.com/groupdiy/albums/userpics/1731_BOM.doc

Important: dont forget the double diode (D2)! And C2 goes to -IN (from base of Q8)

I bought the pins from Ptownkid a long time ago, I think Classicapi have them.
You can even try asking silent:arts if he got some....

Hope this helps.


@mitsos  Im finishing your PCB now in a M1 configuration, JE-16, JH990 and Altran output.
            Very exited about it!  ;D

No sweat, I think back then there had not been as much testing since there were few sources of PCBs and things. I just bought some 1731 PCBs from classicapi and I'm sure there is no 100pF cap on them.  I remember when Fabio's site was still up, he had posted a pic of an o'scope showing a bit of oscillation which went away when the feedback cap was upped by 100pF or so. That was definitely before the dual diode.  I bought a couple of melcors here which were built stock, and I had the same oscillation Fabio had and it went away when I put in the second diode in series, using the normal feedback cap.

Removing the C2 and taking it to -IN, I lost a couple of pads and haven't messed much with the melcors since then (that's why I got the new PCBs)

Sredna said:

Important: dont forget the double diode (D2)!

Click to expand...

Thanks a lot for the BOM and the other informations! 

Sredna said:

And C2 goes to -IN (from base of Q8)

Click to expand...

Didn't exactly got that. Is it an orientation tip for Q8?  ???

Sorry, its simple to do but difficult to explain.  

The left leg of C2 goes directly to the negative in pin (-IN), the right leg goes unchanged in the right hole
in the C2 designation.

Heres the schematic:
http://twin-x.com/groupdiy/albums/userpics/RCA_MELCOR.jpg

Beware that the resistor designations in the schematic differ from your PCB and my BOM, after R4 you have to add 1 to the designation in the schematic. (R5 in schem. = R6 on PCB an so on)

On the PCB R5 doesnt exist, R4 is actually R4+R5 (39.2+4.7= 43.9Kohm)

Ok, got it know. It's easier to see on a picture than to describe in words.  

Thanks a lot for the help.  

Happy building!

Gruesse,

Anders