SAD4096 MN3205 retrofit

[milosch]

Note that the layout above still includes the oscillator cap and resistor, which are not used.  Also, you will need to short the cap at the upper right under my logo.  This is the current schematic:

[dgrech]

Where any further developments on this? Should we conclude that this was a success?

Thanks for the good work! 

[Thomeeque]

Oh man, please don't tell me that you use whole MN3102 only to get voltage divider for V_GG!   You can get the same voltage using two resistors divider, e.g.:

(GND)--[ 14k ]--(V_GG)--[  1k  ]--(V_DD)

Btw. V_GG output should be filtered by capacitor (3.3uF in MN3205 datasheet).

T.

Edit: Sorry, I see now, there was probably some evolution leading to your solution..

This is why I elected to use the MN3102 since it has the correct voltage division.  However, since we don't really need the clock portion of this chip there, I guess a good fixed precision resistor setup for 14/15 (per the spec for the 3205) should work.

so you have not tried to replace MN3102 by divider later?

[milosch]

I haven't tried it but I will at some point.  I got distracted making another board for replacing an R5101 which did need a dual clock.

[Bassisst90]

Sorry to bring up an old thread but I felt this was relevent. I have a DOD 680 delay that I'd been working on for a while but gave up on. The SAD4096 chip works and I have delay so all is fine, but I know it'll crap out sooner or later and would like to make a replacement for when that happens. I found this thread a while ago before I gave up and tried it, but to no avail. I was looking into it again and found this
http://www.e-repair.org/SIA%20Repair/MN3205%20CCT.jpg
http://www.e-repair.org/restoration3.htm
And have tried to plug it into the delay. So far, it did not work but I am not sure I did it right. I got +15v going into the 7808, not 12, and I have like 4-6v going out, not 8. I'm unsure why this is but it may be the reason why it didn't work. Does anyone have an idea of what went wrong?

[Bassisst90]

I just breadboarded the circuit shown on this thread and it did not seem to work at all. Maybe my mn3205 chip is bad? is there a way to check that?

[oldschoolanalog]

I got +15v going into the 7808, not 12, and I have like 4-6v going out, not 8. I'm unsure why this is but it may be the reason why it didn't work. Does anyone have an idea of what went wrong?

If the 7808 is properly hooked up this may be due to a bad part. Double check your wiring. Try a different part if you have one.

Maybe my mn3205 chip is bad? is there a way to check that?

Where did you get the MN3205? In the retrofit I did for the 680 a V3205 was used. Much less expensive.
Do you have a known working MN3205 based delay or access to one? This is probably the easiest way to check your MN3205.

[Bassisst90]

Pardon me. I meant to say I used the v3205. Sorry. And its oriented the way it is pictured in the schematic. I have no other v3205 delay to test that chip on. Maybe I'll just order another of both of these parts

[mimmotronics]

Sorry to bring up an old thread, but my project is relevant to this topic. I am replacing the SAD chip in a DOD 680 with a V3205 retrofit.

I'm powering the clock circuit and V3205 with 8Vdc. I've also removed the 4.7k and 100k resistors originally used to bias the input to the SAD chip. The input is instead being biased on the breadboard at about 4V. So far I've been able to get an output, but my biasing is not consistent with the rotation of the Repeat pot.

I believe the cause is that the 4558 inverting input is biased at 7.445Vdc. Because of that, theres a changing voltage difference across the Repeat pot when I turn it. This, in turn  , changes the DC bias of the V3205's output. I was thinking about powering that op amp with the 8Vdc bus, but I wanted to come here to see how others have been successful with this retrofit before I go down a rabbit hole.

Note: Unfortunately, here in 2018 the pictures posted in this thread don't show up...so if there are any schems to reference please post them new!