Sumo andromeda II - Broken.. - Page 2 - diyAudio
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Old 1st January 2009, 03:27 PM   #11
llwhtt is offline llwhtt  United States
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Not yet, he has not answered my emails. This is a bad time of year to reach someone at their work place if they were gone for the holidays. Next week everything should be back to normal and we'll hear something, I hope.

Craig
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Old 1st January 2009, 07:16 PM   #12
Sponkii is offline Sponkii  Denmark
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Default Craig..

Yes, unfortunately...

really great.. hope you find some thing usefully ..
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Old 11th January 2009, 10:36 AM   #13
redl123 is offline redl123  United States
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Default Sumo

There is a company call Cullan Circuits in CA. Rick does great work repairing Sumo and upgrading.

I am also lookling for a Sumo Gold power amp or the Power if any one knows of one for sale.

Prefer working but not necessary. Thanks Pete
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Old 11th January 2009, 10:14 PM   #14
Sponkii is offline Sponkii  Denmark
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Default repair

redl123

thx. but it is far away, since i live in denmark.. ..
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Old 16th January 2009, 05:26 AM   #15
SQLGuy is offline SQLGuy  United States
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I have an Andromeda II and I rather like it. In fact, I traded in my Andromeda I towards it.

Although they don't have too much in common, both are fully differential amps rated around 200WPC into 8 Ohms and are stable into 4 Ohms.

I managed to blow up my AII a while back (trying to drive a dead short out of one channel). Output devices are MTM20N10's and MTM20P10's - Motorola TMOS Mosfets. The N channels are hard to find and the P channels are much harder to find. I eventually ended up getting a set of them from one of those surplus parts companies that requires like $150 per part number per order minimum (Rayland Corp). I don't believe there are any suitable substitutes for these parts - originals are required.

I'd be surprised if both channels of your amp are blown and the problem is not the outputs. It might be only two or four devices in each channel that are blown, but I'd expect that some of them are.

Have you opened the amp yet? To open it you will need a couple of (English IIRC) Allen keys to remove all the screws that go through the heat sinks on the sides. Then you can lay the heat sink down and see what the internals look like.

If the amp has been driven into a short, the result will be shorted gates of the output transistors, shorted Zener diodes (which were supposed to protect the gates from being overdriven), burned resistors in series with the gates (75 Ohm IIRC), shorted drivers, and burned resistors feeding the drivers. That's what I had to replace in mine. I also had to get extra outputs so I could match them for transconductance. There are two devices per phase per rail that are in parallel, and should therefore be as close as possible to share current evenly.

Mine's been repaired and working fine now for about six months, and I'm very happy to have it back! It's driving the mids and highs of bi-amped Mangepan Tympani IV's.

A high-res photo of one of the boards and heatsink can be found here: http://residentialcolorado.com/images/100_1017.JPG

Cheers,
Paul
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Old 16th January 2009, 07:15 PM   #16
Sponkii is offline Sponkii  Denmark
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Default Paul...

Hey.. thx for the reply..

yes i have taken the amp appart..

i'do not think that it has been driven in to a short, but i'm not sure.

but i know that one channel work, i hav not yet tried to test the other one, because it smelled at first opwerup (no speakers or anything connected), then i took it appart and gave it a look, i could se a bornd resistor...

if to any help i can take som photos of the circiut?..
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Old 16th January 2009, 09:20 PM   #17
SQLGuy is offline SQLGuy  United States
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Definitely. If you can post pictures of the damaged component(s) that would be very helpful.

Do you have a multimeter?
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Old 16th January 2009, 10:09 PM   #18
SQLGuy is offline SQLGuy  United States
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By the way, if you look at the picture I posted above, you'll see that the Zeners under the two MTM20P10s at the left aren't seated well, and that the board under the resistors next to them is darkened. You may also notice the darkened area of the board near C106. These are parts that burn up when the output section is overdriven or shorted.

The interesting thing is that this is the LEFT channel from my amp; I blew, and repaired, the RIGHT channel. This amp was a demo model from a local audio shop that I bought at a discount back when the Andromeda III came out. Apparently, they had managed to blow it and have it repaired at the factory before they sold it to me... or maybe it was a customer that blew it returned it to them. They had told me it was new, but apparently it wasn't enitirely new when I got it. In any case, I haven't had any trouble with that left channel.

On a side note, notice the dabs of paint on the outputs... I guess that's how they marked them for matching. Side note 2: I have since replaced the four bipolar caps in the middle of the board with film types - two are signal coupling and two are for the DC servo.

Cheers,
Paul
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Old 16th January 2009, 11:12 PM   #19
Sponkii is offline Sponkii  Denmark
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Default reply

i sure do, a fluke 177 ..

also got scope and tone gen..

i know a bit about electronic but not much about amplifiers..

after a closer inpection of the amp, and your pic. i found A lot of different thinges, but also different thinges comparing the two channels..

looks like the boken channel have been repaired one time before..

the thinges in () is what i spotted...
R132 is newly burned.
R 232 is intact (or bothe) but seems like it had burned before and replaced
Pot marked is a new one, the original ones are different..

http://img166.imageshack.us/img166/6...rsideddwl9.jpg
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Old 16th January 2009, 11:29 PM   #20
SQLGuy is offline SQLGuy  United States
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If R123 is burned, then Q119 and Q120 are probably blown, along with Q116, CR107 and CR108, and R150 and R153.

Good news is that these are the N channels, which are still sort of available for "only" $37 a piece: http://store.americanmicrosemiconduc.../mtm20n10.html

If the P channels are OK, then you can relatively economically repair the amp. The problem is that that $37 a piece price is for unmatched devices, so it's a gamble as to whether the pair they'd send you would work OK.

Easiest next thing to check is whether CR107 and 108 are short, and also if CR103 and 104 are short. If the first pair is short, then the two N channels are almost definitely blown; if the second pair is short, then the P channels are likely out as well.
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