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Marantz 250M Repair
Marantz 250M Repair
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Old 18th October 2018, 03:07 PM   #71
anatech is offline anatech  Canada
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Marantz 250M Repair
Hi Pete,
It's okay to disagree. What is it about them that you are commenting on?

Like I've said before, I have repaired many of them over a 40 year + period of time and don't get them back. Just happy 250 owners. I even have one for myself.

While it isn't my favorite amplifier, I don't see the need to talk it down without a good reason.

-Chris
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Old 18th October 2018, 03:13 PM   #72
anatech is offline anatech  Canada
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Hi Pete,
I'm still not seeing what you don't like about them. The 510 is likewise a good design, but has some issues over time that are a consequence of the stacked output stage design.
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Old 18th October 2018, 05:25 PM   #73
mjurban is offline mjurban  United States
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I'm kind of on both sides of the fence here.

I bought an early Marantz 240 at the Ramstein Audio Club, part of the PX at the Ramstein Air Base, when I was in the US Army in Germany. This was late 1972 or early 1973. I then proceeded to schlep that amp around through engineering undergrad and grad school, young single adulthood, family, and kids. It was used and abused by me, various housemates in the early years, and later my own adolescent children. I always liked the way it sounded, and it was always the amp in the main system.

At the same time, over the years I would occasionally look at the schematic, and the more I learned and the more experience I got, the more I began to question the design. It definitely had stability issues, because there were additional compensation parts that were roached on to the amp boards after the artwork was finalized and the boards were made.

In about 2009, I noticed the protection circuitry was acting sluggish, in that the relay was taking more time to pull in than usual on startup. Finally, one day it just caught fire. We're talking open flame on the protection board. I was lucky to be there at the time. In trying fit a new relay with different physical form and coil resistance, I managed to fat finger an output, and blow one channel. This one, at least, did not like having its output shorted one bit.

So it sat for a couple of years, but the more I read this forum, the more it screamed out at me to be made into a Leach amp. I took Professor Leach's last artwork, and laid out a new board that fit the Marantz 240 heatsink mounting holes. Turns out this amp chassis, heatsinks, transformer, all the big parts, are just perfect for the Leach circuit. Layout, gerbers, and other artwork for the new amp boards is available if anyone is interested. My boards were made by PCBway, and turned out very well.

Regards,
Mike
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Old 18th October 2018, 08:20 PM   #74
Duke58 is offline Duke58  United States
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mjurban- sounds like my Marantz 1200- purchased in 1972 at Rammstein Audio Club. I bought it off Audiogon in 2013 and have the receipt from the PX.

Because the second owner said the right channel would cut out during play, I replaced the electrolytic caps and rebuilt the relay board. It was my everyday driver for three long years. Then one Friday evening, I was walking over to shut it off and heard some noise and saw smoke coming from the speaker. Got back on Monday and the relay was fried and driver transistors and outputs were fried on one channel. I never have determined if it was the Polk Audio RTA-12 speaker driver shorting or the power amp board frying and began a repair.

There was a guy on AK who helped me out to troubleshoot and repair the board. (We're both banned on the AK forum. Big deal. They advertise as being all about audio, but it's become a social forum for expressing opinions.)

I am interested in more info about the Leach circuit. Can you pm me with the info?
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Old 19th October 2018, 04:56 AM   #75
anatech is offline anatech  Canada
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Hi Guys,
Well, the first rule is, if a piece of equipment behaves out of the norm for it, discontinue using it immediately! That goes for all brands and nothing is immune to that advice. Otherwise you're just asking for it. Right?

Mike, in 2009, how old was your amplifier? It was 37 years old at that point in time. At any point, did you do any real maintenance on it? Also, it isn't uncommon for the design to be changed over the years, and we also get modifications to perform on equipment even after the warranty period is over. Not so much these days, but we did. So, those "roached on to the amp boards" were post work that may have been modifications or changes in the event they had to start using a different supplier of output transistors. Back then, the RCA transistors were a lot faster and required different compensation than most others. Amcron / Crown noted this, many other brands did not (it was a secret I guess). So instead of doing a competent repair, you tossed the guts and installed a different amplifier. You're happy and that's okay. The new amplifier sounds better than the old one did, but mostly because it needed service. After I rebuild them, their owners are quite taken with the improved sound quality. Same amplifier.

It was a total lack of maintenance that caused your fire, and you blew up one channel. It wasn't the amp or the design - just saying.

Hi Duke,
Those Polks killed a lot of amplifiers. They still do today. And of course we have the same complete lack of maintenance too. If you were up here I could rebuild it reliably and also return it to it's original performance or better. There are things that can be done that drop the distortion without changing the schematic in any way. I still rebuild these for people and they perform well once done. Of course, we are talking about an amplifier that is heading for a 40 year old design. If you compare it to some current products, you will see that it's design still runs with the current crowd. Most amplifiers designed in the 60's and 70's sound just awful. Some of the Marantz designs are still better than current product, the 500 being the one I'm thinking of.

It's easy to throw stones at an old design, easier if it failed. But take a good look at the age and situations when they failed. I've done service for over 40 years now, and a lot has crossed my bench over those years. The Marantz brand (until Philips trashed the line) was some of the best designed and built equipment I have seen. There are others, some quirky, but still well designed. Other brands have okay designs and occasionally a great design. Most are like this. Others are 100% hype. That would include most Pioneer stuff, Sony, Aiwa and others. Most equipment wouldn't put up with the abuse most Marantz stuff can handle, and they seldom (but a few do) last even 20 years.

I like a few brands, not just Marantz. I will call them as I see them too, and if those models were "problem children", I would say so. In the case of Marantz, a problem model will have lot's of updates on it to make it reliable. I can't remember whether it's the 2270 or 2275, but that set has a number of mod sheets on it. It is reliable once cared for. At least Marantz took the time and trouble to engineer fixes even after the warranty period.

-Chris
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Old 19th October 2018, 05:22 AM   #76
Duke58 is offline Duke58  United States
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Hi Anatech- I've got a Marantz 1030 and a Marantz 1200 and I really like the sound of them both. I've had the 1200 totally apart at least once, had grounding problems galore afterwards. Learned a lot- didn't know anything about matching transistors, differential pairs, most any problem that could happen happened.

Main reason I like the Marantz is probably psychological- I fixed them. The 1200 is almost 47 years old. I agree that if it was a bad design, it would have crashed and burned by now, especially after all the mucking around I've done on it.
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Old 19th October 2018, 05:40 AM   #77
Diabolical Artificer is offline Diabolical Artificer  United Kingdom
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PB2, you've had the amp now 9 years, have you made your mind up yet what your going to do with it?

Just curious and in no way a criticism.

Andy.
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Old 19th October 2018, 02:20 PM   #78
anatech is offline anatech  Canada
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Hi Duke,
Well, try and rebuild it while applying everything you have learned. While it's apart, do replace the electrolytic capacitors. The small ones are more problematic than the larger ones. If you can, replace the really small electrolytic capacitors with poly - type fil capacitors. If they fit, I use the polypropylene types. Try the same, or polystyrene for the small ceramic capacitors unless the are an NP0 / C0G type.

Matching the input transistors using a jig that I have described in other threads is very helpful. To measure beta, the transistors must absolutely be held at the same temperature. The jig places a pair in a differential configuration and you measure the balance between them. After doing this, match the degeneration resistors if used in that design. Even matching the drivers and outputs will improve the sound quality. This is especially true when multiple pairs of output transistors are used.

These changes do not change the sound of the amplifier, they just reduce the distortion, a lot in some cases.

Best, Chris
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Old 19th October 2018, 02:32 PM   #79
anatech is offline anatech  Canada
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Hi Pete,
I'm sorry, but I missed your post earlier.
Quote:
The 510M looks like it could have been a 1990s design.
I guess, but it was part of the 70's. This amplifier is, I think, the most problematic one in the line. The small film capacitors tend to go open, making the amplifier unstable.
Quote:
Looks like a much better design, might be nice to have
boards to build it into the 250M
Well, the voltages used in the 1200 mean you can eliminate the stacked output design. This would then be an even better amplifier. Of course, you could look at the design of the 2500 receiver and build a scaled down version of that.

I traded my Marantz 510 for a modem back when computer stuff was overly expensive. Looking back, I wish I hadn't done that. That modem was thrown out years ago.

About these amplifiers:
Quote:
I disagree Chris, the amp is obviously flawed.
It is perfectly okay to disagree. What do you find is the biggest problem or problems?

What I have found as the biggest issue with all amplifiers is poor repair work done before. Tis is certainly true of Marantz product where the manual often points out that some transistors are to be matched. or at least replaced with like parts. I often find mixes of transistors in previously repaired products.

Anyway, I am genuinely curious to see what you are trying to point out.

Best, Chris
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