ADA Depot Too - A Forum To Support Users of ADA Amplification Gear

Let's Get Technical => Power Amp Tech => Topic started by: Skitzo on February 14, 2014, 06:11:01 AM

Title: ADA Microtube 200
Post by: Skitzo on February 14, 2014, 06:11:01 AM
Hi all,

I have a microtube 200 amp and it's been great so far!  However, I have no sound now.  When I plug it in, the lights on the front come on indicating power is getting in.  I opened it up and all three fuses are fine.  I also have (believe it or not) an old-school tube tester.  Both tubes are fine.  I don't see any blown capacitors....

Does anyone know of any tricks or known issues on this amp?  (I attached a pic)

Title: Re: ADA Microtube 200
Post by: rnolan on February 14, 2014, 08:50:48 PM
Hey Skitzo, only thing I can see from the pic is the tubes (particularly RHS in pic) could be a little better seated in their sockets, although it doesn't look enough to stop them working.
Apart from the usuall (which you may have done already) spray/clean the pots and sockets this topic may help (http://adadepot.com/index.php?topic=138.0).   The MT200 has a protect mode controlled by a neon bulb.  If that doesn't fix it, then it's over to MJMP et al for more serious fault finding.
Cheers Richard
Title: Re: ADA Microtube 200
Post by: Skitzo on February 14, 2014, 09:36:00 PM
Tell me more about the protect mode....  Perhaps it's just stuck in this mode?
How do I turn it off and on?

Thanks!
Title: Re: ADA Microtube 200
Post by: rnolan on February 14, 2014, 11:51:00 PM
Hey Skitzo, my understanding of it (from this topic which also tells you how to fix it (ADA Microtube - "protect" problems http://adadepot.com/index.php?topic=138.0)) is that when the MT200 warms up, it stays in protect mode (no sound) until the tubes have warmed up.  When the tubes are ready the neon light brings the PSU chip (power supply unit) out of protect mode, you can't switch it yourself.

(From one of Sparkers posts in that topic - "I think when the MT200 PSU startup thing was discussed some time ago, the neon inside the box, NE1 (a NE-2H type) was thought of as a suspect. This neon acts as an under-voltage protection for the PSU chip when the amp is switched on, when the neon strikes on the PSU chip is brought out of shutdown. The neons can degrade over time and the strike voltage can change, also they can show sensitivity to light")

Have a read of that topic (in the Power Amp Tech area), it's where I learnt about it. Cheers R
Title: Re: ADA Microtube 200
Post by: Skitzo on February 15, 2014, 03:35:25 AM
Thanks for the info.  A neon bulb eh?  Did you happen to see one in that diagram I posted?
If that is the culprit, where would I get one?
Title: Re: ADA Microtube 200
Post by: GuitarBuilder on February 15, 2014, 12:03:47 PM
Let's do a systematic check instead of just trying stuff.

First off - do you have the schematics?  If not, download a copy.  They are going to be very helpful.

1.  You say the lights come on.  Is the Protect LED on as well?  If not, then it's not in Protect mode.
2.  Does the fan come on?  If so, we know the transformer is getting power.
3.  Measure the voltages from the power supply.

Do all this and get back to us.  Please be careful inside - the high voltage will hurt you.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 15, 2014, 02:04:35 PM
Yes I have the schematics....but I think it's the protect mode.  I can't get it to turn off.  It's been plugged in for the past 20 minutes and that protect mode light is still on.  Tubes have not heated up and the fan is not running.  The transformer and coil look fine.

Is there a trick to get the Protect mode to turn off?

Thanks!   
Title: Re: ADA Microtube 200
Post by: MarshallJMP on February 15, 2014, 02:57:20 PM
No the only thing you can do is replacing NE1.That soves this problem in 98% of the cases.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 15, 2014, 06:06:00 PM
Damn... I downloaded the schematics at work and now when I try to open hem they won't decompress.  Anyhow, the NE-1 is that Neon Bulb thing?  Where would I get one of those? 
Title: Re: ADA Microtube 200
Post by: rnolan on February 15, 2014, 10:37:29 PM
From MJMPs previous post on ADA Microtube protect problem topic ("Only the MT200 has the protect  led.This is because it's the only ADA amp that has a switching power supply.Like sparker said,change the neon bulb and the problem will usually be solved.Let me know if you can't find one,i have a few lying around.") so MJMP may be able to get you one although my understanding is it's not a hard part to buy.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 16, 2014, 02:50:20 AM
I PM'd MJMP - you guys are awesome!! Thanks for the help! I hope the bulb is the solution.  I don't live anywhere near an electronics store. So perhaps he still has one or someone can put me onto an online store?

You know how it died.... I was playing a gig and using the amp to power a couple small monitors.  A bunch if people were dancing really close and a guy stepped on the 1/4 cable going into the monitor.  He bent it and sent a signal back to the amp putting it in protect mode forever and ever. Next tone I buy monitors or PA speakers, they will be powered.
Title: Re: ADA Microtube 200
Post by: Sparker on February 16, 2014, 06:07:06 AM
I PM'd MJMP - you guys are awesome!! Thanks for the help! I hope the bulb is the solution.  I don't live anywhere near an electronics store. So perhaps he still has one or someone can put me onto an online store?

You know how it died.... I was playing a gig and using the amp to power a couple small monitors.  A bunch if people were dancing really close and a guy stepped on the 1/4 cable going into the monitor.  He bent it and sent a signal back to the amp putting it in protect mode forever and ever. Next tone I buy monitors or PA speakers, they will be powered.

Hi Skitzo - wish you had said this to start with!! If it wasn't in protect mode before the speaker stomping guy, you may have something blown / short in the output or PSU stage. It could also be in protect mode because of this.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 16, 2014, 06:23:02 AM
Sorry, but it did work after he stomped it. But not for long - we were able to finish the set.  I took it to the electronics teacher at the school I work at and we tested everything we could and it all appears fine....  Which is why I think you're correct with NS1 being the variable.  We never even thought that it could be a factor. 
Title: Re: ADA Microtube 200
Post by: Sparker on February 16, 2014, 06:32:51 AM
Hi Skitzo, well it's an easy hit to change the neon anyway, so carry on as planned and let us know :beer:.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 24, 2014, 07:55:45 PM
Hey Sparker,

I haven't been able to get in touch with MJMP so I tried ADA Tech suppor and didn't hear from them.  So, I'm just on a hunt for the NE1 bulb.  The one question I have is - Should the bulb be coupled to the unit?  I took the cover off the power supply and found the bulb and it got this white goop on it attaching it to the unit. Should it be like that?  Does it matter? 

Any idea where I can find an online catalogue and order and NE1 bulb?  (Sorry about the quality of the picture)
Title: Re: ADA Microtube 200
Post by: Skitzo on February 24, 2014, 08:39:00 PM
Hmm I think the neon bulb is ok.  It's lighting up.  But it's still on protect mode.  Fan not turning and tubes not heating up. Could it still be faulty even though it's lighting up?
Title: Re: ADA Microtube 200
Post by: Skitzo on February 24, 2014, 09:14:40 PM
pic
Title: Re: ADA Microtube 200
Post by: Sparker on February 25, 2014, 08:32:59 AM
Well, the amp could be in protect mode because there is an actual fault with the PSU or output stages, due to previous mentioned speaker wire stomping issue.

I think MJMP said he had some of the neons, but he might be doing a very thorough brewery inspection at the moment   :beer: :beer: :beer: :cheers: :givemebeer:  But I don't think there was anything particularly special about the neon.

Do you still have access to your electronics guy at school? I could give him a list of things to test.
Title: Re: ADA Microtube 200
Post by: Sparker on February 25, 2014, 11:12:46 AM
Quick test: With the power off, case off, pull the fuses from both the amplifier boards (where the tubes are), either side of the big round power transformer. Power back on see if still in protect mode.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 25, 2014, 11:36:29 AM
I've been swapping the fuses around to see if I could find a fault - but didn't try running without fuses.  Won't that just leave a broken circuit?  I'll try it as soon as I get home.  BTW I finally got the schematic diagrams to open.  I attached them to this message in case anyone else wants them. 

Yes I can hit the electronics guys up at school also.  PSU eh....
Title: Re: ADA Microtube 200
Post by: MarshallJMP on February 25, 2014, 01:22:23 PM
From what i can see (and i'm no PWM expert) that if the neon is on there is current flowing trough it so this should be fine.I saw there is also a overtemp switch T2 that should be closed during normall operation.So if Q1 conducts (The neon is on)and T2 is closed the shutdown input should have around 0V (else it would have 14.3V on the input (pin 10 of U1) of the SG3524 PWM controller).Another thing connected to the shutdown input is D12 R23 R24 network.I think this is sensing the current going trough R22 (0.15 ohm/5W) resistor.So if the current is too high it will trigger the shutdown input.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 25, 2014, 01:49:05 PM
I removed the two fuses like you suggested and its running!  The fan is going and the tubes are warming. I have not plugged a guitar or monitor into it.  So I assume this is a fuse issue and replacing them will fix the problem...,
Title: Re: ADA Microtube 200
Post by: MarshallJMP on February 25, 2014, 02:30:30 PM
So you pulled the fuses from the amp boards (3A)?If so and it works now chances are that the fuses are good but one or both poweramps have a shorted output.(one or more busted power MOSFET).Try to put them back in one at a time and see what happends.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 25, 2014, 07:55:34 PM
Ok... So I put one fuse in on channel B and nothing on channel A and it worked.  Then I put the same fuse in channel A and nothing in B and it did not work.  So it looks like something in channel A is not working. 

Any ideas?

It's so odd that removing a fuse makes it work.... Ha!  So what would happen if I tried it out without that one fuse in channel A - Would it work?
Title: Re: ADA Microtube 200
Post by: rnolan on February 25, 2014, 09:18:53 PM
Sorry, but it did work after he stomped it. But not for long - we were able to finish the set.  I took it to the electronics teacher at the school I work at and we tested everything we could and it all appears fine....  Which is why I think you're correct with NS1 being the variable.  We never even thought that it could be a factor.
So I'm guessing the lead that got stomped on was from channel A ? (given that B now works as long as no fuse in A) so as MJMP says, one or more busted power MOSFET
BTW the zip file won't open (unzip) for me, complains about being spanned across multiple disks.
Title: Re: ADA Microtube 200
Post by: MarshallJMP on February 26, 2014, 04:56:17 AM
So channel A is busted.By removing the fuse you also shutdown the excessive current going to the A channel.That is one of the advantages of a switching power supply,it will go into protect mode when the current is too high.If it would have a regular power supply the fuse would just blow every time.

Now my guess is that one or more power mosfets are shot.Usually if one fails it takes the rest out too.And in some cases also the drivers.So best thing to do is replace them all,so both the drivers as the power mosfets.

So that means Q2 to Q9.DON'T skip out on one.Replace them ALL.

Q2,Q4,Q5 MPS8099 0.5$/piece
Q3 MPS 8599 seems to be obsolete but you should find them on ebay.
Q6,Q7 IRF 9530 3.50$/piece
Q8,Q9 IRF 530 3.30$/piece

Found these on the mouser website.So it will cost like 16$ to repair.Not the end of the world IMO.
Title: Re: ADA Microtube 200
Post by: Sparker on February 26, 2014, 06:49:54 AM
Don't forget new thermal grease or pads on devices where required. Try not to re-use if gunked up or gone hard, cracked, etc, and make sure the area is clean and free from lumps before re-applying new stuff. Also, that neon was probably spiked to the metal post with mastic/RTV to stop it vibrating, might be best to re-apply some of this.  :thumb-up:
Title: Re: ADA Microtube 200
Post by: Skitzo on February 26, 2014, 09:11:08 AM
Thanks for the info!  I'm a beginner at this so bear with me. I can't seem to upload the schematics I have because it's 7 megs.  But  I got it from here   

http://www.eserviceinfo.com/downloadsm/52183/ADA_microtube200.html

There are three parts to the download for some reason. 

Sorry to be such a pain. I'm looking at the schematics and trying to find the parts you say I should swap out.  You found those parts on ebay?

I think I'm over my head here (and finding the time to research and find the parts...).  I've never pulled a transistor off a board and re-soldered one on. Damn.. those MOSFET's look fine - nothing pulled off, no damage....

I guess I can use that one channel that does work eh? Run it until it blows and then scrap the whole thing.... I just use that amp for monitors when we're on stage. 

If I tried the other channel without the fuse in it - it would eventually blow the tube right?  What would happen?

Title: Re: ADA Microtube 200
Post by: MarshallJMP on February 26, 2014, 02:38:42 PM
Good thinking Sparker,forgot to mention that!

Skitzo,where are you from?Maybe i can point you to a good electronics store?Parts should be easy to find.

Changing them is another thing,don't you know someone that has some good soldering skills?

Yes you can use only 1 channel,no problem.

The other channel won't work without the fuse in it but nothing else will happen,the tube will survive this.
Title: Re: ADA Microtube 200
Post by: Skitzo on February 26, 2014, 04:55:30 PM
I love close to Guelph Ontario - I work in Georgetown which I in the Greater Toronto Area. 

All I have here is an old soldering gun. Ha!
Title: Re: ADA Microtube 200
Post by: rnolan on February 26, 2014, 07:57:56 PM
Hang in there Skitzo, between MJMP and Sparker, they'll help get you through it.  Maybe the electronics teacher where you work can help you, or you could give it to a competent tech to fix for you.
Title: Re: ADA Microtube 200
Post by: GonadiusPrime on March 19, 2014, 08:19:56 PM
An old soldering gun and a little of your time is all it will take.  The procedure MJMP speaks/types of is really easy to do.  The schematics and layouts on this site will help out.  Good luck man.
Title: Re: ADA Microtube 200
Post by: Skitzo on March 20, 2014, 04:47:33 AM
Well I have the specs I just need to know what's what.  What to pull off to swap out.  It seems like one side is actually working. Everyone here has been so helpful. It's now a question of identifying the part and finding the replacement. If I swap out all kinds of parts I'm afraid ill bust something - so one at active may be the ticket. 
Title: Re: ADA Microtube 200
Post by: Dante on March 20, 2014, 10:50:34 AM
Swap out one part at a time, test it after every step.
Title: Re: ADA Microtube 200
Post by: MarshallJMP on March 20, 2014, 03:44:38 PM
Normally i advise people to change one thing at a time but in this case you need to change them all in one go.
Problem here is you don't know what is busted.If you replace the wrong one (one that works) the bad part can destroy the other one.Let's say you have a bad driver and you leave it in,and you just replace the power mosfets,that bad driver WILL destroy the 2 powerfets.That's why i say replace everything,this way you are 100% sure everything is new and in working order.
Title: Re: ADA Microtube 200
Post by: Skitzo on March 22, 2014, 05:59:51 AM
My feeling is that it is the MOSFETS but ya, I agree swap them all out.  I just still need to find where I can get the parts. Ugh
Title: Re: ADA Microtube 200
Post by: GonadiusPrime on March 22, 2014, 07:40:20 AM
I think I ended up going to DigiKey because they're kind of local.  Bought each component in lots of 10...I think.  The parts aren't hard to find, or at least they weren't.
Title: Re: ADA Microtube 200
Post by: GuitarBuilder on March 22, 2014, 11:12:44 AM
I don't want to sound contrarian, but asking a non-experienced person to replace the MOSFETs is pretty high risk.  I think Skitzo would be much better off taking it to an experienced amp tech with the information/schematics gathered here.  He'll have it back in working order in no time.

I had a Microtube 200 with the same symptoms (one dead channel) and it ended up needing two resistors replaced as well in addition to one of the MOSFETs.  It took me multiple hours of troubleshooting with an oscilloscope to figure it out.
Title: Re: ADA Microtube 200
Post by: rnolan on March 22, 2014, 11:44:39 AM
Hey Skitzo, tend to agree with GB here, if you're not comfortable (hey, if you are, DIY), or, get a tech to do it for you (that's why god invented techs...))
Title: Re: ADA Microtube 200
Post by: Skitzo on March 22, 2014, 02:42:05 PM
Honestly, it's not worth sending out.  The only reason why I'd fix it is to simply gain some experience in fixing amps.  It'll cost most than the thing is actually worth and I was given it anyhow.  I have a 300 w dual channel TOA amp I'm using now.  So if I could somehow figure out which MOSFET - ill give it a go.  I now have a little more electrical gear. 
Title: Re: ADA Microtube 200
Post by: MarshallJMP on March 22, 2014, 03:51:03 PM
Skitzo,mail me,we'll figure something out.I'll get to you on monday.