My Micromoog is blowing fuses!

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ChuckFalcon
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My Micromoog is blowing fuses!

Post by ChuckFalcon » Sat Jul 01, 2017 6:00 pm

Hi everyone! I went on a craigslist hunt for a guitar and ended up finding a dusty old keyboard tucked away in a corner on the way. This keyboard was a Micromoog, which I got as is and untested. Cosmetically it was in super condition so it was worth a gamble. I bring it home, fire it up, and get nothing. Pop it open, blown fuses. I get fresh fuses, pop 'em in, turn it on, I get power for about one second and then both fuses blow.

All of the wiring and solder joints look to be original and it doesn't look to have seen any rough use. Does anyone have any ideas of how to get started fixing this thing? Replacing caps in the power sections? Testing the transistors on the power supply board? What are your ideas. Any and all help is very much appreciated.

Thanks,
Chuck

ChuckFalcon
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Re: My Micromoog is blowing fuses!

Post by ChuckFalcon » Sat Jul 01, 2017 6:36 pm

another clue, I popped in 2 more fuses and unplugged the socket coming from the transformer to the power supply board. Fuses didn't pop and I am getting 20V off of the power supply. I hope this helps and can help someone tell me something.

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Re: My Micromoog is blowing fuses!

Post by Mooger5 » Mon Jul 03, 2017 3:26 pm

I googled "micromoog tantalum" and came across this thread:
https://forum.moogmusic.com/viewtopic.php?f=1&t=17636
You still won´t get better advice from other than the late KL.

Cheers.
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ChuckFalcon
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Re: My Micromoog is blowing fuses!

Post by ChuckFalcon » Tue Jul 04, 2017 10:47 pm

Mooger5 wrote:I googled "micromoog tantalum" and came across this thread:
https://forum.moogmusic.com/viewtopic.php?f=1&t=17636
You still won´t get better advice from other than the late KL.

Cheers.
Thanks for the read! Very interesting. I ended up taking out the power board and started testing the diodes. All tested fine EXCEPT CR104. I ordered some diodes and then some filter caps for good measure. One of the caps in the power section was also way out of spec. Im still waiting on my order, but hopefully when the diodes come in I will be posting good news!

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Re: My Micromoog is blowing fuses!

Post by Mooger5 » Wed Jul 05, 2017 12:01 am

So if you unhook the PSU from the mainboard the fuses still blow? The shorting component is then in the psu, most probably. Good thinking.
best of luck.
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Re: My Micromoog is blowing fuses!

Post by ChuckFalcon » Wed Jul 05, 2017 8:42 pm

Mooger5 wrote:So if you unhook the PSU from the mainboard the fuses still blow? The shorting component is then in the psu, most probably. Good thinking.
best of luck.
OK, new diode is in and new fuses in, fired it up. The fuses are still alive!!!......and a new problem...I plug the audio out to the pa and try to play and this is what I get: Very very quiet synth sounds. I twist all the knobs and switches and all variations. It won't get very loud at all however, all of the controls seems to be effecting the sound properly.
ALSO: As I turn up the volume knob it doesn't increase the volume of the synth but it DOES increase the volume of the "key clicks" when I press the keys.

I poked around with an audio probe without looking at a schematic and I AM getting normal volume synth sounds.

Can you make heads or tails of this?

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Re: My Micromoog is blowing fuses!

Post by Mooger5 » Wed Jul 05, 2017 9:59 pm

Chuck, by "key clicks" do you mean loud pops/thumps? If so, that´s an easy fix :)

The VCA has to be calibrated. There should be a trimpot for that. I´ll have to direct you to the service manual for the optimal procedure. It´s a simple task, but I´m sure it´s explained in a better way than I could provide 8-)

Cheers.

Also, you might have to do the same for the Taurus.
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ChuckFalcon
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Re: My Micromoog is blowing fuses!

Post by ChuckFalcon » Thu Jul 06, 2017 4:55 am

Mooger5 wrote:Chuck, by "key clicks" do you mean loud pops/thumps? If so, that´s an easy fix :)

The VCA has to be calibrated. There should be a trimpot for that. I´ll have to direct you to the service manual for the optimal procedure. It´s a simple task, but I´m sure it´s explained in a better way than I could provide 8-)

Cheers.

Also, you might have to do the same for the Taurus.
Oh boy, looks like I'm in trouble. I'm not getting the pops/thumps anymore when I hit a key. I am still getting very quiet synth sounds now. I took a look at the manual to test and according to the manual, something is wrong with my VCF, because I'm not getting noise sound in one particular location. I pulled all the transistors in the VCF to test them and they all test good, now I'm testing caps. I just put in an order for some of the IC's that I may have to replace.

Oh boy, what a journey I am now on. :banghead:

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Re: My Micromoog is blowing fuses!

Post by Mooger5 » Thu Jul 06, 2017 11:05 pm

Sorry to hear that. Replacing components like that should not be advisable unless you´re really good at desoldering. If you´re taking that extra care though so the pads and traces don´t lift off in the process, then I don´t see why you shouldn´t replace the CA3046 chip. That one´s a probable culprit. This, of course, only in case you don´t hear any cutoff frequency changes and the resonance going into self-oscillation.
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ChuckFalcon
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Re: My Micromoog is blowing fuses!

Post by ChuckFalcon » Fri Jul 07, 2017 4:02 pm

Mooger5 wrote:Sorry to hear that. Replacing components like that should not be advisable unless you´re really good at desoldering. If you´re taking that extra care though so the pads and traces don´t lift off in the process, then I don´t see why you shouldn´t replace the CA3046 chip. That one´s a probable culprit. This, of course, only in case you don´t hear any cutoff frequency changes and the resonance going into self-oscillation.
Yeah, I've made the mistake in the past and lifted pads and traces on an Akai mpc 1000. I have since then got a Hakko FR-300 desoldering iron, and it is SUCH a breeze. I put in an order for some IC's. I'll follow up as soon as they arrive.........from China :roll:

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Re: My Micromoog is blowing fuses!

Post by Mooger5 » Fri Jul 07, 2017 8:49 pm

Please report back.
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ChuckFalcon
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Re: My Micromoog is blowing fuses!

Post by ChuckFalcon » Fri Jul 28, 2017 1:35 pm

Mooger5 wrote:Please report back.
Alright, after some time I got the IC's in the mail. I replaced all the CA1845E, CA3080E, CA3046E chips, tested all diodes and transistors and I STILL am getting no sound out of the output.

At this point, I'm really at a loss. You have any ideas what could be going on?

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Re: My Micromoog is blowing fuses!

Post by Mooger5 » Fri Jul 28, 2017 5:09 pm

There is a path for the audio signals. Last time you probed around and found good audio levels without looking at the schematic. That´s OK. It´s a starting point. Now you should do the same, this time while looking at the schematics and take notes. There must be a point somewhere where the signal is interrupted or something.

Is everything OK with the PSU now? All voltages present? Measure if the power is arriving intact at each chip.

Moog schematics are great for troubleshooting, I find. They even tell you what voltages to read at certain key points.
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Re: My Micromoog is blowing fuses!

Post by synthchaser » Sun Aug 27, 2017 3:36 am

If you got the ICs from China, they're probably fake. You haven't ruled out those chips yet...

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