Posts Tagged marantz

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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Marantz AV7005 – Home Theater

6527948817_ace4721f6b_mFunny (short) story: I wasn’t actually ready to step up to the AV7005, but our Denon receiver in the library was “gifted” with some cat vomit through the top cooling vents; I didn’t know it had happened, because the back of the receiver was through-wall and sort of invisible inside a closet on the other side of that wall. So the Denon just kept on working until eventually, the acid in the vomit actually ate through some of its wiring. Nice, eh? Silly cat.

So the Denon went downstairs into my shop, where it will likely sit until the weather warms up (our basement is cold!) and I”m willing to sit there, rip it apart and fix it. My Sony 7.1 receiver then moved from our home theater to our library (and I built an anti-cat cover for the unit, there will be no more “vomit surprises”), and then I picked up the Marantz AV7005 and some MA-700 amplifiers to serve in our home theater — I’d been eying this specific unit for a while, and well, as I told She Who Must Be Obeyed, “the cat made me do it.” I can’t say I’m depressed over the upgrade, but this wasn’t exactly how I thought it would come about.
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