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Author Topic: ADA Microtube 200  (Read 17175 times)

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Skitzo

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Re: ADA Microtube 200
« Reply #15 on: Time Format »

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?
« Last Edit: Time Format by Skitzo »
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Skitzo

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Re: ADA Microtube 200
« Reply #16 on: Time Format »

pic
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Sparker

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Re: ADA Microtube 200
« Reply #17 on: Time Format »

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.
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ADA Gear: MP-1 Tube Board

Sparker

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Re: ADA Microtube 200
« Reply #18 on: Time Format »

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.
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ADA Gear: MP-1 Tube Board

Skitzo

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Re: ADA Microtube 200
« Reply #19 on: Time Format »

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....
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MarshallJMP

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Re: ADA Microtube 200
« Reply #20 on: Time Format »

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.
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Skitzo

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Re: ADA Microtube 200
« Reply #21 on: Time Format »

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...,
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MarshallJMP

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Re: ADA Microtube 200
« Reply #22 on: Time Format »

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.
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Skitzo

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Re: ADA Microtube 200
« Reply #23 on: Time Format »

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?
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rnolan

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Re: ADA Microtube 200
« Reply #24 on: Time Format »

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.
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MarshallJMP

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Re: ADA Microtube 200
« Reply #25 on: Time Format »

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.
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Sparker

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Re: ADA Microtube 200
« Reply #26 on: Time Format »

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:
« Last Edit: Time Format by Sparker »
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ADA Gear: MP-1 Tube Board

Skitzo

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Re: ADA Microtube 200
« Reply #27 on: Time Format »

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?

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MarshallJMP

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Re: ADA Microtube 200
« Reply #28 on: Time Format »

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.
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Skitzo

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Re: ADA Microtube 200
« Reply #29 on: Time Format »

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!
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