B22 dead, what to do?

[guzziguy]

Be sure you insert it in the proper orientation. It wouldn't do to have it backwards.

[dsavitsk]

Following instructions that Nate gave me, I took the fuse out and verified that it was indeed blown. That was easy, will be getting a new fuse soon.

Proper fuse size is 1.33x the VA rating of the power transformer. Most here use power transformers that are hugely overrated meaning that the fuse is often very large for the circuitry. If that was the case here, you should figure out why the fuse blew as this should not happen under normal operation. This is particularly the case since it happened at a meet so you have no idea what the cause was. Good luck

[spritzer]

Yeah, the fuse blew for a reason. Meets and B22's don't mix well so taking pix of the amp boards for use to see could be a good move. Look for charred parts next to the large heatsinks...

[Asr]

Finally got a set of new fuses today and installed one right away once I got home.

Unfortunately the new fuse blew almost immediately - I saw the power light turn on for a very brief instant but it went out almost as quickly. I re-opened the amp but nothing looks damaged as far as I can see, and no weird smells either. Sounds like there'll be some troubleshooting to do...

Definitely never taking the B22 to a meet again I think.

[n_maher]

Steve,

Post the specs of the fuses that you bought please.

And a clear internal shot of the amp with the cover off would be great too, if you can.

[luvdunhill]

I bet Nate will have some ideas, but in general replacing a fuse and hoping for the best can be a dangerous proposition. That said, you could disconnect the amp boards and still see if you blow the fuse, but again you really should bring the amp up more carefully...

[n_maher]

The funny thing is Marc, I've never had a blown beta22 blow fuses. Even the ones with cooked output stages would still turn on. I can't fathom what non-visible failure of this amp would cause it to draw excessive current at startup. But I'd certainly like to see some pictures before Steve throws another fuse in and hits the button.

[digger945]

Sigmas don't play nice with non slow blow fuses, even on the bench with nothing connected. I don't thing I have ever used more than a 1 amp slow blow, even for 2 sigmas.

Very frustrating.

[kevin gilmore]

disconnect the power supply output to the amp boards, insert new fuse and see if it blows.

If it does, its the power supply board (shorted diodes, or shorted caps) or a shorted transformer.

If it doesn't blow hook up the boards one at a time.

[Asr]

Could a moderator move this thread to a certain other sub-forum? Will wait to post pics until after the thread is moved (don't want bandwidth being used up unnecessarily).

Nate, I got 2A 250V fuses (slow-blo), same spec as the fuse that was already in the amp. I haven't tried another fuse btw, didn't think that would help anything. I don't know how to disconnect power to the amp boards either, so I can't try that.

[Augsburger]

Yep. Though bit different than typically known Kansai-ben since I'm from the eastern region of Kansai.

I thought they were interchangeable, my grandfather used the terms with equal frequency.

Sorry to hear this is still troubling you Steve.

Edited August 21, 2010 by Augsburger

[HDen]

Could a moderator move this thread to a certain other sub-forum? Will wait to post pics until after the thread is moved (don't want bandwidth being used up unnecessarily).

Nate, I got 2A 250V fuses (slow-blo), same spec as the fuse that was already in the amp. I haven't tried another fuse btw, didn't think that would help anything. I don't know how to disconnect power to the amp boards either, so I can't try that.

Do you think you could actually keep the thread here? I don't have access to that other subforum, and I'd like to know this since it might be of use in the future(maybe to others too). If you need a host for your pictures, you can send them on to me and I'll upload them to my server.

[Asr]

Ok, let's keep the thread here then.

Hi-res pics (1920x1440, so not quite Gilmore-sized but still big enough I think) have been uploaded here: http://www.crystalsynth.net/nb22i.zip. This ZIP file will be deleted in 30 days.

The very last pic in the set is something I noticed while doing a closer inspection, missed it before, thought it might be related.

[Pars]

Just looks like some flux in the last picture. You've been given good advice... disconnect the amp boards from the PSUs (the red/blue/black groups in pic 3) and see if the PSU comes up with no load. Does this B22 have a single sigma22 or two? If so, disconnect them both. The wires I pointed to go to the amp boards, so you won't have any loose wires with voltage on them floating around doing it this way. If you were to disconnect them at the amp boards, then you have to worry about that.

If you have a DMM and the PSU comes up, connect the black lead to one of the sigma22 terminals marked G. Set the DMM to DC volts (and if not autoranging, to greater than 30), then take the red lead and touch the V+ (terminal that a red wire is going to now), and then the red to V- (where the black wire is going). You should see +30 for the first and -30 for the second.

Edited August 21, 2010 by Pars

[deepak]

Steve the Head-Case attachment limit is quite large so in the future you can attach high res images to your posts and not have to worry about your bandwidth.

[Asr]

Thanks for the info Pars, I went ahead and tested power without the amp boards and then Left and Right individually. DC voltage readings came out at plus/minus 29.6V on both channels, I'm guessing that's close enough though?

Ok, bad news first: I ended up with yet another blown fuse, but just 1 fortunately. The good news is that I was able to isolate where it's coming from. With both of the amp boards disconnected, the amp powered up ok. It's probably a good thing I tested the Left amp board first, as it powered up and stayed on - but the Right amp board did not and the fuse blew almost immediately with it connected instead. So now that I've verified the Right amp board is the cause, what now?

[n_maher]

Steve,

With the amp board disco'd from the power supply measure the following:

V+ to G

V- to G

output to ground

[n_maher]

Steve,

With the amp board disco'd from the power supply measure the following:

V+ to G

V- to G

output to ground

[Pars]

Steve,

With the amp board disco'd from the power supply measure the following:

V+ to G

V- to G

output to ground

Nate,

Are you asking him to ohm these out?

Steve,

I believe Nate means to use the ohms function on your DMM to measure the resistances between the points indicated. This should (may?) show you what area is shorted.

[kevin gilmore]

Yep, first thing is hook up the working channel and make sure the output voltage is zero before

doing anything else. If it really is zero, and you have some "el-crapo" headphones you don't care

about, hook it up and see if it sounds ok.

Pull the dead amp board out, and look for pieces of metal, or other things that don't look right.

But if its shorting out the power supply completely, most if not all of the output transistors are

completely toasted. (or the bias supply transistor, and or pot are trashed)

[Asr]

Steve,

With the amp board disco'd from the power supply measure the following:

V+ to G

V- to G

output to ground

A little confused, where do I place the probes to measure those? The previous

[n_maher]

I'll try to call tonight Steve.

EDIT: this thread wasn't meant to be locked, not sure why my phone did that...

Edited August 23, 2010 by n_maher

[Asr]

I finally got around to having the amp fixed and got it back yesterday. Set it up and it works great. Glad to have a working B22 now.

According to the person who fixed the amp, the 4 output MOSFETs in the right-channel amp board were blown so they were all replaced. Not going to identify who fixed the amp as he requested anonymity. Big thanks to him though.

Edited March 13, 2011 by Asr

[mrarroyo]

Glad to see all worked out for you thanks to the "undeclared fixer person". Enjoy it!

Edited March 13, 2011 by mrarroyo

[Augsburger]

Yes it is nice to have "guardians" watching over your shoulder and X2 thanks to the anonymous fixer upper. Enjoy Steve!