Archive for category Things that are Busted

Marantz MA700 troubleshooting

I have quite a few Marantz MA700′s; of the group, four of them exhibit random popping sounds of moderate energy at the speaker output with no audio input to the unit. Clearly this is a very common failure mode for the MA700.

I have opened one of the “poppers” up on the bench, and with the buffer amplifier signal cable to the power amplifier disconnected, the popping noise remains, so it’s definitely not in the audio path on the buffer amplifier board. The buffer amp is connected to the power amp via an electrolytic, so there’s no problem unplugging the buffer from the power amp.

There’s another problem with this unit, too: I see somewhat random engagement of the high power rail mode for the amp, but this is not co-incident with the clicking coming from the speaker.

When the high/low power state switches randomly, the associated relay clicks, which is audible at very low volumes, and this is obviously not the design intent. Erratic high/low power switching problems are going to be nearby QU05, very likely the electrolytic CU08, the diodes DU01 and DU02, or QU05 itself. I’d suspect CU08 first.

The main amp PCB shows evidence of excessive heating towards the front of the chassis, where the driver section is located. Unfortunately, it looks to me that the mechanical assembly is complex with regards to the main amp and attached heat sink; taking it apart looks to be quite a big deal, my vision has become very poor, and I don’t actually need the amp, so I’m just going to close up. However, at least this exonerates the buffer amp and provides a pointer as to how to troubleshoot high/low rail power issues.

If anyone locates a specific component that is responsible for the clicking and popping, I would very much appreciate hearing about it; I’m willing to hack in a replacement electrolytic from the component or solder side of the board if that’ll solve the problem. Likewise, if circumstances lead me there — if one of my working MA700′s fails and I really need to fix one of these “poppers” — I’ll post what I’ve learned.

I’ve put the service manual for the MA700 online here.

–Ben, AA7AS

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WLO RTTY News Feed Replaced with Weather

Sad news for RTTY SWLs, WLO’s newsfeed at 8473 kHz is gone, replaced with weather broadcasts. The weather broadcasts alternate between RTTY and SITORB, just as the news feed did, but that’s the end of the similarity.

Well, it was nice while it lasted. Sigh.

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Cellphone Etiquette at the Table

Wandering though life, I often encounter the occasional person who seems to have missed an etiquette class. Or several. In particular, I have noticed that a very large number of gaffes occur at the dinner table. So as a gift, I provide the following guide to using your cellphone when sharing dinner with family, friends, and friendly companions:

Rule #1: Don’t.

Rule #2: See Rule #1

If your phone rings, vibrates or plays an obnoxious ringtone (all ringtones are obnoxious) there is only one polite action: Turn it off or mute it, while apologizing: “I’m sorry, I forgot to turn my phone off. Fixed!” Slip it back in your pocket and deal with it later.

In an upcoming post, I will cover cellphone use during conversation with another person. I’m sure you all look forward to that.

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The 2012 Election – I Surprise Myself

8142797777_17cc1e55ec_nDeb and I had the pleasure of meeting some of the key democratic candidates for office for, and within our state (Montana) today. Each spoke for a few minutes about their aspirations, and spent some time “working the room”; I bent a couple of ears, as anyone who knows me might expect, and got some fairly good answers, actually.

I don’t normally jump on a soapbox, politically, but this year… here we go.
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The Constitution is not just a piece of paper

rippedObama has (and let’s be fair here — also the congress, and the judiciary, and state officials have) repeatedly demonstrated either a complete disrespect for, or absolute misunderstanding of, the constitution.

From the inversion of the commerce clause, ex post facto laws at both the federal and state levels, sweeping usurpation of article 5 powers via the judiciary, to blatant violations of the 1st, 2nd, 4th, 5th, 6th, 8th, 9th, 10th and 14th amendments, our government is — at best — operating in an unauthorized fashion, wielding powers it was never granted by the people, and ignoring its obligation to protect the rights it was explicitly charged with protecting in return for being allowed to operate at all.
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Predicting where IOS and OS X will go

Every time I read one of the sycophantic articles predicting OS X is going to become like IOS, I have to laugh. That’s not going to happen, at least, not in the long term. So in the spirit of the new year, when every fool (I’m speaking most definitely of myself here) proceeds to stuff foot deep into mouth, I offer the following IOS, OS X, iPad and iPod predictions:
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But mom…


When I was a young fellow, I lived in a fine house on a gentle hillside in Pennsylvania. We had a barn, about a hundred feet away, which had an upstairs, where we parked the car; a loft, where we kept some ducks; and on the reverse side of the barn, downhill, an entrance to its basement, as it were, where we kept various things such as the lawnmower, the odd length of lumber and so forth. In between the house and the barn was gentle hillside, carefully mowed, bordered with forsythia and pussy-willow, which flattened out into a 3/4 acre lawn. Altogether a lovely and pastoral place to grow up.

One summer evening, my mother asked me to fetch something from the bottom of the barn. It may have been a gallon of paint; I vaguely remember something like that. Anyway, I shook my head emphatically, no! I was young enough, or she was gentle-hearted enough, so that the response wasn’t getting boxed about the ears (which, IMHO, would have been the right response) but instead, an inquiry as to why not.

I told her, earnestly: “I might get struck by lightning bugs!”

She laughed, and to tell the truth, I don’t know if she made me complete that errand, or not. What I do know is that it cemented my memory of those little flashers — and her merry laugh — permanently.

That house — and the yard, and the hillside — is still (barely) under my family’s control. The federal government took it in a land grab for the Tock’s Island dam project, a project they failed to complete, although they certainly ruined a lot of people’s lives and homes in the process. But my mother, being pretty darned sharp, negotiated a deal with the feds that she could stay there, and the house around her, until or unless the water actually was going to rise. She guessed right, and that never happened.

So I have occasion to visit the place. One of the things that saddens me when I visit is that the fireflies (lightning bugs) are gone. Where once they turned the yard into an amazing display that looked like a thousand fairies dancing, now there is just darkness.

The town (Milford, Pennsylvania) has grown into an over-crowded, over-taxed, over-illuminated tourist trap. I suspect that has something to do with it. Perhaps the overuse of insecticides played a part as well. All I know for sure, though, is that place is significantly diminished by the lack of fireflies.

At least I have my memories. Not so much for kids who grow up in the area now.

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Cocoa/OSX console messages: Could not setup Mach task special port 9: (os/kern) no access

11949894331101577697bomb_01.svg.thumbEver run into this one? Under Leopard (OSX 10.5.8), the above message is posted to the system console every time cron launches a process. If you use cron for anything and the console for anything, this can be very, very annoying. Apple’s known about the problem for years, and has done nothing. Since I fall into that class of folks who use both the console and cron, I’ve been more or less quietly steaming about it. I finally decided to do something about it. Be warned; the following is technical and to-the-metal hackery. Don’t try this at home unless you’re very confident in your skill(z).

Now, as this hack is fairly specific to the problem, I don’t think it can hurt anything else (if performed correctly), and it serves my needs perfectly. Your mileage may differ for any number of reasons, and if you’re not a technical person, you should stop reading now and just forget your ever saw this post. Really. Stop now.
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