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VCO Problems

2009-07-31 by spacebardubs

Hey y'all
I'm new here and this is the first post I've made, so Hello.

I just built a bunch of MOTM modules, all of which work great, except for one boneheaded move I made. I accidentally plugged in one of my 300 VCO's to the power supply while it was on. And it arced and started smoking. I was pretty sure that it was U6 that was smoking, so I replaced it. Unfortunately it's not going to be that simple and I am now officially stuck.

I did all of the troubleshooting tips in the manual and have ended up with some very suspect voltages. At L1 I have -15V, but at L2 I have only +.9V.
In keeping with the list to check in the maunal:
a. Pin 1 of U2 should be close to +5V. I have +0.15V
b. VX should be close to +4.8V, I have nothing at all.
c. The left side of R37 should be near +0.32V, I have +0.05V
d. VREF on the left of C15 should be +5V, I have +0.15V
e. With a sweep of the Coarse knob, Pin 7 of U4 should range from -8.3V to +8.3V, I get -2.13V to +0.11V
f. With the same sweep pin 1 of U4 should range from -0.3V to -14.2V, I only have a constant +.25V

The other very strange thing is that when I plug this 300 in to try and troubleshoot, it seems like it's somehow shorting out the rest of the modules plugged into the power supply. My other VCO no longer makes any sound and the LED on the front of the 101 stops. When I take the defunct 300 out everything works fine again.

Any tips as to how to proceed would be greatly appreciated!

Thanks in advance.

Jesse

Re: [motm] VCO Problems

2009-07-31 by mcb, inc.

On Fri, 31 Jul 2009, spacebardubs wrote:

Show quoted textHide quoted text

> Any tips as to how to proceed would be greatly appreciated!

1. *STOP* plugging it into your power supply. It's clearly
not operating anywhere near normal conditions if it is
affecting other modules.

2. Component ignition, like shooting a module with a
shotgun or flinging it with a trebuchet, is outside the
scope of a troubleshooting checklist. If you don't know
why U6 smoked (we certainly don't) you can only guess at
what is damaged and hope random or total parts replacement
fixes it. And check every single solder joint, component
and wire.

--
Monty Brandenberg

Re: [motm] VCO Problems

2009-07-31 by Graham Atkins

Jesse,

Re check the 300, you must have a short on the power rails
somewhere on that module. Plugging it in with the frame
powered up would not normally cause a problem of that
nature. That is why you have practically nothing on the 5V
rail.

Graham

Show quoted textHide quoted text

On 31 Jul 2009, at 03:49, spacebardubs wrote:

> Hey y'all
> I'm new here and this is the first post I've made, so Hello.
>
> I just built a bunch of MOTM modules, all of which work great,
> except for one boneheaded move I made. I accidentally plugged in one
> of my 300 VCO's to the power supply while it was on. And it arced
> and started smoking. I was pretty sure that it was U6 that was
> smoking, so I replaced it. Unfortunately it's not going to be that
> simple and I am now officially stuck.
>
> I did all of the troubleshooting tips in the manual and have ended
> up with some very suspect voltages. At L1 I have -15V, but at L2 I
> have only +.9V.
> In keeping with the list to check in the maunal:
> a. Pin 1 of U2 should be close to +5V. I have +0.15V
> b. VX should be close to +4.8V, I have nothing at all.
> c. The left side of R37 should be near +0.32V, I have +0.05V
> d. VREF on the left of C15 should be +5V, I have +0.15V
> e. With a sweep of the Coarse knob, Pin 7 of U4 should range from
> -8.3V to +8.3V, I get -2.13V to +0.11V
> f. With the same sweep pin 1 of U4 should range from -0.3V to
> -14.2V, I only have a constant +.25V
>
> The other very strange thing is that when I plug this 300 in to try
> and troubleshoot, it seems like it's somehow shorting out the rest
> of the modules plugged into the power supply. My other VCO no longer
> makes any sound and the LED on the front of the 101 stops. When I
> take the defunct 300 out everything works fine again.
>
> Any tips as to how to proceed would be greatly appreciated!
>
> Thanks in advance.
>
> Jesse
>
>
>