Smoked my MB200!
MB200 with MP3 and headphones plugged in, decided to connect my 210, 8 ohm cab. Plugged in the cab's 1/4" plug, turned on the amp... DONE! Smoke, smell and static. Power LED stayed RED, didn't go BLUE.
This set of connections is nothing new. It worked fine two nights ago and on several other occasions. I'm thinking that when reaching around the MB200, connecting the 1/4" cable by feel, my knuckle accidentally pushed in the switch that changes the headphone jack to a line out.
Thing is... I've had this 'accident' before. Sound was not right. Checked it out and found the line out switch pushed in with headphones connected.
I'm wondering if these 'accidents' degraded the component to the place where this last time was the final straw. Apparently the protection circuit doesn't cover everything!
So, for the moment, my practice rig is a Behringer 802 mixer with headphones. Glad I have SOMETHING!
Pics attached. GK tech support has my email in their in-box. Asked for prices for repair or a new main circuit board.
Do you think that's what did it... line out activated with headphones still plugged in?
I could be talking out my wazoo, but the frying shown occurred on the outsourced ICEPower board, which is what actually pushes the cab. The line out / headphone functionality is probably handled by GK's own "auxiliary" circuitry and should be unrelated to the failure, especially going down the way you describe - trying to drive headphones with line output shouldn't have caused any problems.
What I'm having a hard time telling is exactly *what* kind of component that is that went up on smoke on the ICEPower board, but in any event I don't think this can be chalked up to user error, unless you've been in there poking inside the MB200's guts before.
OK, again, Not An Expert, but looking at the datasheet for the ICEPower board, that Molex connector / header labeled P103 is an auxiliary power supply, which probably feeds power to the GK circuitry (the IP has its own onboard power supply). The thing that blew *appears* to be a form of board-mounted fuse, so basically the GK part of the circuit asked too much of the ICEPower's power supply when you switched on.
I also see nothing in the MB200 manual that warns against "accidental misuse" of that dual-purpose 1/4" jack, and I can't think of any good reason why you'd get "bad sound" out of the speaker out with an incorrect setting on the *line / headphone* out. Either there's a bit of a design flaw here or you may have had a quietly defective unit to begin with.
Thanks for your compassionate and informative reply!
I'll post GK's tech support response.
No, manual has no cautions against 'accidental misuse' of the combo jack.
The bad sound I referred to was in the headphones which were possibly overdriven.
Wherer did you find info on the ICE board?
Sounds like a power on failure, nothing to do with the 1/4". Driver and/or output MOSFETs in the power amp, probably.
Hopefully, GK will sell me a board.
Ideally, they will feel badly enough to just give me one! Well... maybe at cost. That would be nice.
I really like this little amp. Hope to save it.
The PDF data sheet for the board is here (I am assuming it uses the 50ASX2 BTL, which is basically the same board - sure looks the same as the one in your pics). You have to scroll through a bit to find the explanation of the various header pinouts, including P103. The ICEPower modules are pretty common in most of the commercially-made class D microamps; it's my understanding Aguilar uses the same board(s) for the TH series.
And yeah, the headphones wouldn't sound so great being pushed in line-out mode. Depending on the phones, quite possibly overdriven. Sounds like there was just some kinda fluke, but it still looks to me like the fault occurred off that aux power tap and probably lies in the GK circuitry doing something it shouldn't have on power-on.
The bummer about all the SMD technology is that what used to be a 10 minute, $20 fix by a decent electronics tech now requires replacing an entire board. I guess the positive side is boards are easy for anybody with some common sense to replace at home.
But I agree, I wouldn't waste any time worrying that you did something wrong. I think it's a coincidence it happened when it did.
...Hey, another fellow Okie! Maybe!
That board actually looks like it *could* be fixable by a tech. The thing I'd worry about-- and worth mentioning to OP-- is whether the fault condition that caused the board to smoke that (possible) fuse has magically gone away; it could be something where a new board will just have the same problem on first power-up. I'd send it back to GK for a look if feasible.
Thanks for the link!
Yes, being an electrician, I always wonder why the breaker tripped or the fuse blew.
I'm interested to hear what GK tech support has to say and will post their reply.
Here's a pic of a raw ICEpower 50ASX2 board.
Notice on the inboard choke there's no temp sensor. This must be a GK item. You can't see it in my original pics, but it's held on with a zip tie. I'm assuming it is transferable.
New board on Ebay is $100, shipped.
Then I still haven't answered the question - why did this happen.
It looks like there are two different versions of that board. One is stereo, and the other is bridged (the BTL) and B&O-rated at 220x1 into 4 ohms. The GK almost certainly contains the latter, as the stereo board is only rated for 50x2. The two boards probably use the same proprietary ICEPower chip as their guts but I don't know how difficult it would be to "talk" the stereo board into becoming the mono BTL board.
I'd still send it back to GK. My guess is that they will probably supply the board to you at that cost or lower if it req's replacement. (edit: and let *them* blow a perfectly good ICEPower board at their cost if they fail to check the rest of the circuit first. :) )
If you don't a fast reply from the generic email addy, a good direct contact is firstname.lastname@example.org.
I'm not going to say it, but you know darn well I'm thinking it.
Oh, a handful of GK fans have been all up in the PF500 threads complaining about them having occasional problems and using GK as an example of how to do things right...meanwhile this is about the 4th or 5th thread this week alone about the MB series having problems. But that's apparently OK because it's GK and not the evil Ampeg empire.
It holds true that anything made by man can fail no matter who makes it. Even nature has failures.
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