Mother-32 dead after brief 2 pin polarity inversion

[moebius]

Hi fellow moogers!

I'd be greatful for any advice on what to replace or check on my Mother-32 mainboard. I did not identify any fuses or protection diodes near the 2pin power header.

I've had a little mishap with my Mother-32. I was using it in my eurorack perfectly fine and decided to rehouse it in its original desktop case. By mistake I inverted the polarity of the internal 2 pin power cable and briefly tried to power it. With no lights coming up, I rechecked and realized my mistake. Luckily no white smoke or smells. But now it shows no reaction trying to power up with the original PSU, nor does it with my 10pin->16pin cable to the doepfer power bus.

Here are my test point readings, if this helps:

GND / TP1 (+12V) : 1.67V
GND / TP2 (-10V) : -0.22V
GND / TP3 (+5V) : 0.75V
GND / TP7 (+10V) : 1.65V
GND / TP9 (+3.3V) : 0.08V

The power source is outputting the correct 12V DC.

Thanks!

[Stevie Ray]

I'd be very surprised if the Mother 32 didn't have basic diode protection against reverse polarity connection. I think it's on the main board, not the little sub-board with the DC jack and headphone amp. How on earth did you managed to reverse the *polarised* connectors dude?

Double check that all the connectors are properly seated. If in doubt remove them and re-seat them. That's the 2-wire and the 5-wire between the little sub-board and the Mother main board - they should only go on one-way without forcing them. Do the 2-wire (black/geen) connection first, and see if your Mother powers up. The 5-wire connection is only required for the audio output.

If no joy, try powering it from your Eurorack again and see if it works. If it does then there's a connector problem between the sub-board and the main-board, if it doesn't work, you've screwed the pooch

-- EDIT --

You might find my response to this thread useful "Putting Mother Back in Her Case: --- http://forum.moogmusic.com/viewtopic.php?f=19&t=25423

[mmarsh100]

How on earth did you managed to reverse the *polarised* connectors dude?

Eurorack power connectors are notoriously easy to reverse - there's no key, only a red stripe *sometimes* :/

At the op: I think it may be a case where you'll have to send it in for repair. Even if there are diodes to protect the circuit, they are almost certainly SMD. Probably best to let a pro handle that, unless you have some experience. Very sorry to hear this, the Mother is a great synth, I would *hate* to have anything happen to mine!

[moebius]

Good question Asking myself, duh...

The two pin power connector with the cable sticking out towards the backplate seemed to be too tight, so it made more sense to me to connect the cable facing inward at that time, it was dark and the plastic guides are easily bent. I successfully connected and disconnected the eurorack cable without inverting the polarity, so I'm a bit stumped it happened on the 2pin connector. I also already tried to power it again via eurorack bus. Still dead.

I had already freed the mainboard and measured the testpoints directly from it. The little power jack / audio out board just directly passes the power from the jack to the header cable. And surely moog put some polarity protection on the mainboard?

I am capable of soldering smd parts (got an air reflow station) and thought someone might be able to point me in the direction on what to measure or replace.

Thanks for your sympathy to this tragic event

[moebius]

I've measured some of the parts following the power input traces. Looks like the board is two sided with a ground pane inbetween.
I've checked the diodes, resistors and capacitors in that area and I'm suspecting one of the following two diodes and coils:

Mother-32 power input diodes and coils

D2, Marking "LE 4AA" - TVS Diode? Maybe a SMBJ12A? Can someone confirm this?
My readings are unclear on this one

D4, Marking "DI 547 B140" - Diodes Incoporated Schottky Barrier Rectifier B140 40V
Can measure electricity flow in both directions. Without schematic I don't know if the diode's bust or the reverse flow is from the layout.

Also I'm not sure about the two coils visible there (L20 and L23). Can anyone tell me the proper values for these?

[Stevie Ray]

I've measured some of the parts following the power input traces. Looks like the board is two sided with a ground pane inbetween.
I've checked the diodes, resistors and capacitors in that area and I'm suspecting one of the following two diodes and coils:

mother32_diodes_coils.jpg

D2, Marking "LE 4AA" - TVS Diode? Maybe a SMBJ12A? Can someone confirm this?
My readings are unclear on this one

D4, Marking "DI 547 B140" - Diodes Incoporated Schottky Barrier Rectifier B140 40V
Can measure electricity flow in both directions. Without schematic I don't know if the diode's bust or the reverse flow is from the layout.

Also I'm not sure about the two coils visible there (L20 and L23). Can anyone tell me the proper values for these?

I am sympathetic, honestly. I've done things like that many times over the years but have mostly gotten away with it.

You sound like you have plenty of technical knowledge so I don't really have much more to add.

Without schematics it's hard to say what might have broken, or why, or what needs to be replaced. Seems incredible to me that Moog didn't incorporate reverse voltage protection, especially as they provide a non-keyed header for Eurorack power (which poster above correctly says is easy to reverse) --- actually that wouldn't make any difference as the Mother only uses the +12v and 0v - all other pins are NC.

I can only suggest you ask Moog tech support.

I'd be interested to know what they say and whether you find a solution.

Best of luck.

Steve

[moebius]

Yeah, thanks!

I actually wrote an email directly to the Moog support guys a week before opening this thread, but haven't heard a word yet. Not even a "we don't help DIYers" or something.

Totally different from what I am used to from Doepfer here in Germany.

I'll update this thread with any movement on this

[moebius]

And she is alive again! Woohoo!

Turned out I had to replace R51, which had changed its resistance. It's a small SMD resistor, so this might not be for everyone.

Kudos to the Moog suppport team, got a really nice mail with some ideas and that nailed it!

[Stevie Ray]

Great news!

Curious to know what R51 is though. Resistors don't change values even in reverse polarity?

Moog tech has always come through for me. Also Dieter Doepfer - I've asked Dieter the stupidest questions sometimes and he always responds in a courteous and professional manner.

Good to hear your M32 is back in business

[grenert]

What is the resistance of R51 supposed to be? The Mother seems to be based on the Werkstatt, and it has a 4.99R resistor inline with the 12V input that has burned out on people (like me) who have used incorrect power supplies.

[moebius]

What is the resistance of R51 supposed to be? The Mother seems to be based on the Werkstatt, and it has a 4.99R resistor inline with the 12V input that has burned out on people (like me) who have used incorrect power supplies.

The smd resistor has a 2R00 marking, it has a resistance of 2 Ohm.

[Stevie Ray]

Sounds like a current limiting resistor if it's in series with the +12v supply. I guess it's possible for it to burn out if the current draw in reverse polarity exceeds its power rating. Not a great design I'd have thought. Diodes are plenty cheap!