Help! I blew up my MC202!! :( *Fixed! Thank You :)

[JRock]

Here I am with another synth problem...

I figgered this was the place to ask since Phono is the reigning expert on the MC202

I was using it to send CV to an SSM2044 module I'm designing. I sent the CV out and played my DR110 audio through the SSM2044. I switched some wires around on the pots for the filter module. I couldn't get the CV to control the envelope and when I tried the audio from the MC202 all I hear is little clicks. Sounds almost like digital noise but it's not as breathy and it goes up and down with the volume control.

I would imagine that I accidentally sent + or -15V into the CV output
Where should I look? What should I do? I pulled out the diode D34 and tested that. It read off one way and 5.5 the other way. I can hear the VCO if I stick a headphone into IC23 and I can hear the Sub on IC17 (4030)...

If this is the wrong place to ask I apologize. But I know Phono knows them backwards and forwards... Just check out DINSYNC.info

Thanks

[JRock]

Look at the Service Docs. My guess is I blew up IC14 the HD14066BP (4016). I'll wait to hear something before I switch it though....

[phono]

Make that www.dinsync.info (edited your post)

Your best bet is to try and trace the signal with a scope from the mixer section, you can read it right off the faders. Also try switching the gate/env switch. Check also that the filter is still working. And finally the vca.

[JRock]

My bad. I knew it was wrong Thanks for changin' it and for the response. I just don't think it's sending them CV. The CPU is fine. I can still program stuff on it... It just doesn't play! It's late here so I'll bust out my scope and start tracing stuff first thing in the morning.
Thanks again!

[JRock]

Ok. The whole analog section isn't getting negative power. The TL062s ICs18, 19, 20 are getting 12V on pin 8 and the CEM3340 is getting 7.5V on pin 13. I'm not getting any signals from any of the chips after IC14 the HD14066BP. I get a nice square wave off of the Sub IC17, but that's neither here nor there. Seems like There is a little noise coming off of IC15 MC14052B. I have another HD14066BP I pulled out of one of my scavenge boards but I don't know what a quadruple analog switch/multiplexer does So I don't know if it's the right thing to change or not.

Seems like that's where things stop working in between the built-in synth sequencer and the analog synth section....

[guest]

if you were only using the cv out
of the mc202
then ic20 is the most likely culprit

check your powersupply first
what are the voltages on c25 and c26
then check for 5.333v 12v and -5.3v
on ic10 an ic9

[JRock]

Damn Guest How do you know this stuff? You are the Man!!!

Ok. Seem s like the Power is screwy maybe.
C25 is 15.3V
C26 is 8.6 V

IC 10 seems pretty normal. IC 9 seems not right. I'll list everything, cause I'm not absolutely positive what i'm looking for.

Pin 1 2 3 4 5 6 7 8
IC9 .36 .14 .14 -4.6 0 2.58 .16 16.25
IC10 5.33 5.33 5.33 0 5.33 5.33 11.84 14.45


Thanks for helping

[guest]

there is definitely something wrong
with the negative rail

its either getting pulled up by a short
or ic9 is faulty
turn of the power
and measure the resistance to ground
from ic9 pin7

you may also want to pop ic20 out
and see if the negative voltage rail comes back

[JRock]

IC 9 : Pin 7 resistance to ground is 5.6 Ohm...

I'm gonna go ahead and pop out IC 20.
If that's all it is I got another TL062 right here next to me.

I'll post up as soon as I get out and check things.

Thanks!

[JRock]

Still no good on the negative rail. I replaced IC 20 and it's still the same. Do I need to replace IC9?

IC 14 wouldn't have anything to do with it?

[guest]

its not likely ic14
what makes you suspect it

pull out ic9
and see what the resistance to ground changes to
there is definitely a short someplace
unfortunately a lot of things connect to that rail

is any part getting warm
are any of the eletrolytic capacitors blown

[JRock]

Hey. Sorry, I've been diggin' out and doing this and that for the last couple of days. I pulled IC9 and resistance to ground on pin 7 is 5.9.
The negative rail is still no good.

I don't see any funny looking caps or shorts...

I thought it might be IC14 cause the signal kind of bottlenecks there... I'm not sure why.
In the schematics it's in between the digital stuff and the analog stuff, I think.

Thanks so much for taking the time to help
I hope whatever you're doing you're making a million dollars doing it.

[guest]

its always difficult to hunt down a short

you can either start removing everything
that connects to that rail
and see when the short goes away

or you can measure the resistance
between that rail and ground
at each component it goes to
and see which one has the lowest resistance

another technique is to use a current limited powersupply
and feed in a volt or so at 50mA
and measure the voltage drop at each chip
or look for things getting warm

[JRock]

How would it have gotten a short?

[guest]

something must have gotten destroyed
when you plugged in the cv
so the short is inside a component

what was the exact sequence of events you went through
before the synth stopped working
are you sure your connector went to the built in synth cv out