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Advice for fixing a faulty Neumann M149a power supply

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Advice for fixing a faulty Neumann M149a power supply

Postby jondo » Wed Jun 28, 2017 9:03 pm

About 2 weeks ago I purchased a 2nd hand M149 mic, and was very happy with it until it stopped working yesterday. The symptoms were after leaving the mic on for several hours during a session, i noticed more background noise in the signal path when usually it was quiet as a mouse. I turned off the m149a power supply, but then it didn't turn back on.

So I changed the fuse in the plug, no joy, then opened it up to see if there was another fuse inside, nope. after testing with a voltmeter, it looks like the faulty part is a cheap looking PSU inside made by Globtek that is soldered at two points onto the circuit board and switch.

Now i'm not the king of electronics, but i think even i could fix this one, but the PSU model is Globtek Switching Adapter GT-21089-1512-T2, which I can't seem to find anywhere. Written on it is Output 12v 1.25A, 15w max, it takes a 2 pin power cable. Obviously don't want to get this wrong, does anyone know where I could source an equivalent PSU to carry out the repair myself of similar or superior quality?

Thanks
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Folderol » Wed Jun 28, 2017 9:34 pm

Can you post a picture?
Should be do-able, but difficult to suggest without seeing it.
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby jondo » Wed Jun 28, 2017 10:31 pm

Thanks for your reply. Can't see any option to upload photos here so have placed them here

https://1drv.ms/f/s!ApBwcIMmBsgnijzS5rlnwBQVRqX3

This one might be a replacement candidate, but there's nothing mentioning switch mode on it.

https://www.amazon.co.uk/Pike-Co-Branded-PI315-12-DESOCKETOP-x/dp/B00LRWNVQ0/ref=sr_1_65?s=computers&ie=UTF8&qid=1498682569&sr=1-65&keywords=12v+power+supply+1.25a
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby ef37a » Thu Jun 29, 2017 5:57 am

Pin 1: –70 V
Pin 2: +5 V
Pin 3: audio signal (+phase)
Pin 4: +70 V
Pin 5: sensor line
Pin 6: ground
Pin 7: +32 V
Pin 8: audio signal (–phase)

Those ^ are the voltages that should come from the supply. THAT supply does not look like anything mssrs Neumann would produce!

If I have the right model we are looking at a £3000 microphone? I suspect that getting the PSU or its connections wrong could damage the mic and I would urge you to find the correct supply from a Neumann agent. Expensive? Probably but it could get much worse IMHO.

Last but CERTAINLY not least. Are you qualified to safely poke about in mains powered devices and are you certain you can leave them in a safe state for other people? Anytime you have mains kit apart and work on the '230V' side said kit should then be PAT tested.

Dave. http://www.studiocare.com/neumann-n149- ... gLKDfD_BwE
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Folderol » Thu Jun 29, 2017 8:39 am

Hmmm, does look a bit sus. Initially I was wondering if it was a dual conversion - mains to stable DC then DC to actual wanted voltages.
However, you said it had worked, so that still may be true. Is there any indication that a different input supply might once have been fitted?
That supply in the picture is a bog-standard one of a type that is readily available all over the world. wioth the mains side pre-packaged and double insulated, so unlike Dave, if that's the correct voltage I wouldn't see a problem replacing it with the same type.
The one below would seem to be a (slightly improved) replacement - provided you get the output polarity right!
http://uk.farnell.com/xp-power/vet18us1 ... dp/2708280
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby ef37a » Thu Jun 29, 2017 9:28 am

OK Will, maybe I am being a bit over cautious but you have to ask...Why did that PSU fail?

Does not look like heavy duty required nor restricted airflow? SMPSUs are generally UBER reliable.

But, FTF, I hope OP at least has a decent digital test meter!

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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Hugh Robjohns » Thu Jun 29, 2017 10:45 am

Personally, with such an expensive mic, I'd contact Sennheiser UK (assuming you're in the UK -- else your local Sennheiser/Neumann agent) and get them to repair it properly. That way ensures guaranteed performance and future resale value...

I may be wrong, but I gather that PSU (N149a) has evolved a bit over the years.

Current models have an IEC mains inlet, rather than the C7 fig-8 type which was employed on older units. But they do all appear to use a universal switched-mode PSU module to supply 12V to the PCB, and that board then uses DC-DC conversions to provide all the power rails required by the valve mic.

Using an OEM PSU module is a routine technique to get around all the different international safety legislation... but like Dave I'd be a bit horrified to discover the OEM PSU simply stuck to the inside of the case with double-sided tape. Not at all what I'd expect in a £3k mic with a Neumann badge on the front.

I'm intrigued... Anyone else got an M149/M147 mic with the N149a PSU that can open the box and see what's inside for us?

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Re: Advice for fixing a faulty Neumann M149a power supply

Postby jondo » Thu Jun 29, 2017 3:49 pm

Thanks for all your replies, I had already sent in a request for repair quote to Neumann thats come in at £300 fixed fee. I also sent photos of the unit to them and they have been really helpful and confirmed it genuine and that globtek psu is used.

Ive establshed no volts are coming out of the globtek, it also has bulging leaky caps inside, Sennheiser spares are charging £200 for its replacement, so I will try and source it direct from the manufacturer.

I'm certain i can undertake this repair safely, it involves one replacement psu soldered in two places that are well away from anything else (on the switch and pcb). Dave totally understand the need for safety/caution, believe me if it was anything more complicated I wouldn't be doing this, and I do know someone who can PAT test it afterwards.
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby jondo » Thu Jun 29, 2017 4:02 pm

Hugh, there is a metal support cage that held the psu, I took that out before it was photographed, so the trickiest part willbe finding a psu that will also fit that cage. I did own an M147 before buying this that had an IEC power connector, never went wrong in 15 years, so never opened it up, the only difference i noticed was that this newer N 149a is lighter than the other before I sold it.

Just bad luck that it's gone wrong in 2 weeks, and I don't think the mic is anymore than 5 years old if that, it's immaculate.
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Hugh Robjohns » Thu Jun 29, 2017 4:31 pm

jondo wrote:Sennheiser spares are charging £200 for its replacement, so I will try and source it direct from the manufacturer.

Hmmm... I wish you luck with the one. Appreciate £200 is a bit steep, but a least it will have the correct output wiring and maintain the integrity of the whole thing.

Pleased to hear aot the cage -- that restores my faith! ;)

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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Folderol » Thu Jun 29, 2017 5:59 pm

That's one hell of a mark-up for a PSU that costs about 10 quid trade :( Even a 'medical' grade PSU is less than £50.

Are the connections on the board marked + and - ? if so, there's no doubt what I'd go for. Yes, yes, I know that's easy from me to say but... :wave:

P.S.
If it was me I wouldn't need them marked - many years experience replacing anonymous dead PSUs :)
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Sahib » Thu Jun 29, 2017 6:12 pm

At the end of the day the decision is yours but I would not hesitate to use an off the shelf power supply. I do not think there is anything special about that Globetek.
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby jondo » Thu Jun 29, 2017 8:47 pm

I've found what i hope is an almost identical Globtek replacement it's the same manufacturer, same model number, 12v 1.25A 15watt, appears to be the same size. The only differences is max input current says 0.5A instead of 1A on the label of the current one, can anyone tell me if that lower input current is going to cause a problem, I have no idea what the tube in the mic might actually use whilst on, but because the psu can still provide max output 1.25A, that should be OK right?

Also it doesn't say switching on it, just ITE power supply, but I'd hope that with it being the same model, that's it's the same.
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Folderol » Thu Jun 29, 2017 8:57 pm

jondo wrote:I've found what i hope is an almost identical Globtek replacement it's the same manufacturer, same model number, 12v 1.25A 15watt, appears to be the same size. The only differences is max input current says 0.5A instead of 1A on the label of the current one, can anyone tell me if that lower input current is going to cause a problem, I have no idea what the tube in the mic might actually use whilst on, but because the psu can still provide max output 1.25A, that should be OK right?

Also it doesn't say switching on it, just ITE power supply, but I'd hope that with it being the same model, that's it's the same.
I'm wondering if they are playing games with the rating. Like you can draw 15W but only briefly :( It's highly suspicious if it has exactly the same model number. The numbers don't make sense, but if it is rated at only 0,5A it will almost certainly be inferior, and likely to fail early. If anything you should go the other way and fit one with a slightly higher current rating. I'd be very surprised if you couldn't get one in the same size package. These things have shrunk dramatically over the last few years.

Hardly any PSUs have the word switching these days, it's more-or-less assumed that it will be.
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Sam Spoons » Thu Jun 29, 2017 9:09 pm

If it's a 'world wide' power supply, it may be rated at 1A for 115VAC which would mean it would be rated at 0.5A for 230VAC....... I suppose it depends on the target market.....
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby jondo » Thu Jul 13, 2017 6:07 pm

Just an update on this, the replacement power pack arrived from the US, I've soldered it in, and fortunately there's no sparks, smoke and tears, just a green power light that is now on :D

Left it on for an hour to make sure it didn't subsequently explode, then turned off and sheepishly connected the M149 mic to it and........... happy days fully working again, been on for 10 hours now and no problems.

The cost, £4 + postage, but i did also buy an extra 2 spares, just in case.

Thanks for everyone for their advice who helped me get it working again.
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby Hugh Robjohns » Thu Jul 13, 2017 6:26 pm

Excellent... and a lot more pleasant than the £200 plus option.... :D

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Re: Advice for fixing a faulty Neumann M149a power supply

Postby yannlu » Tue Jan 29, 2019 11:08 am

I had the same problem with mine. A pad of the mains connector in the Ault SPSU has broken and started to burn. Probably due to the mechanical traction. After fix it I got 12VDC again on its output. I checked all the voltages but probably something else failed in the main board. Is someone has the schematics of it ? Thanx

ef37a wrote:Pin 1: –70 V
Pin 2: +5 V
Pin 3: audio signal (+phase)
Pin 4: +70 V
Pin 5: sensor line
Pin 6: ground
Pin 7: +32 V
Pin 8: audio signal (–phase)

Those ^ are the voltages that should come from the supply. THAT supply does not look like anything mssrs Neumann would produce!

If I have the right model we are looking at a £3000 microphone? I suspect that getting the PSU or its connections wrong could damage the mic and I would urge you to find the correct supply from a Neumann agent. Expensive? Probably but it could get much worse IMHO.

Last but CERTAINLY not least. Are you qualified to safely poke about in mains powered devices and are you certain you can leave them in a safe state for other people? Anytime you have mains kit apart and work on the '230V' side said kit should then be PAT tested.

Dave. http://www.studiocare.com/neumann-n149- ... gLKDfD_BwE
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby gdowling » Mon Feb 18, 2019 11:19 am

Just wanted to say thanks for the info here.

My 2 box style power supply failed last night before a session today, after reading the advice here I was able to use a spare 12V switched mode power supply to get it working again.

Will do a proper job at some point - but would never have attempted it without the thoughts here.

Thanks guys!
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Re: Advice for fixing a faulty Neumann M149a power supply

Postby crescentmoon66 » Sat Feb 23, 2019 10:02 pm

Here is a link to the actual model and part..... https://en.globtek.com/search/?q=TR9KE1 ... &x=11&y=13
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