A long time ago I bought a second hand Marantz 250. And life was good. Until it wasn't. For no obvious reason, one day several years ago, the music died.
As I recall, I thought the left channel went DC, and I pulled the power ASAP. That said, I can't confirm that that is what happened.
At the time, I had a quick look and couldn't find anything obviously wrong with a visual inspection. However, it was evident that someone had been in there before me. All the transistors had been replaced (with the left side completely mismatched), a few resistors replaced, and the relay on the protection board was moved (poorly) with long leads to the front in order to accommodate a larger relay. There may be other changes I haven't yet noticed.
Without the time, I put it aside and used a Rotel amp I had with the idea of fixing the Marantz "later". Fast-forward several years to today, when the left channel of the Rotel stopped working. Now I have no amp and am looking at the Marantz again.
I pulled the transistors to test them, and they all seem OK, to my surprise. Not at all matched, but no open or closed shorts.
I decided to plug it in to see what happened, as it had been so long and I couldn't remember what I had seen. When I did, the meters did their usual bounce, and nothing else. But when I turned on my preamp, nothing else happened. The meters just sat there motionless (and they did work just fine when last used). I hooked up some old test speakers, and nothing.
I noticed that the protection relay also just sits there when the amp is turned on. No click. No movement. Does that indicate a DC current trying to get to the speaker outputs?
Anyone have any ideas? Where should I start? I don't have endless money or time to spend on this, but I'm willing to put in a few hours and a couple hundred bucks.
Thanks!
As I recall, I thought the left channel went DC, and I pulled the power ASAP. That said, I can't confirm that that is what happened.
At the time, I had a quick look and couldn't find anything obviously wrong with a visual inspection. However, it was evident that someone had been in there before me. All the transistors had been replaced (with the left side completely mismatched), a few resistors replaced, and the relay on the protection board was moved (poorly) with long leads to the front in order to accommodate a larger relay. There may be other changes I haven't yet noticed.
Without the time, I put it aside and used a Rotel amp I had with the idea of fixing the Marantz "later". Fast-forward several years to today, when the left channel of the Rotel stopped working. Now I have no amp and am looking at the Marantz again.
I pulled the transistors to test them, and they all seem OK, to my surprise. Not at all matched, but no open or closed shorts.
I decided to plug it in to see what happened, as it had been so long and I couldn't remember what I had seen. When I did, the meters did their usual bounce, and nothing else. But when I turned on my preamp, nothing else happened. The meters just sat there motionless (and they did work just fine when last used). I hooked up some old test speakers, and nothing.
I noticed that the protection relay also just sits there when the amp is turned on. No click. No movement. Does that indicate a DC current trying to get to the speaker outputs?
Anyone have any ideas? Where should I start? I don't have endless money or time to spend on this, but I'm willing to put in a few hours and a couple hundred bucks.
Thanks!
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The speaker relays here, disconnect the amplifier from the speaker to prevent start-up and shut-down thumps from disturbing you and also any significant DC voltage on the outputs from the power amplifiers - when there are amplifier fault conditions. The plan is to determine whether its a DC problem and how bad or just a timing delay problem with the anti-thump circuit.
What to do for starters though, is locate where those amplifier outputs connect to the relay contacts on the relay-rectifier board and measure any DC volts there. Anything more than say, 100 mV is bad news and anything between say 30-100mV is not a big deal but should be looked into.
A DMM and a couple of small clip leads should suffice for testing at this stage but check out the troubleshooting guide too, for interest, here and locate the power/relay board before taking matters into your own hands - this is not for beginners when things have been messed with already and perhaps left in a poor state. Things to look at are the small timing caps on that board - for some reason they are often the nemesis of simple output protection circuits.
Don't forget the lethal mains potentials around the power supply - safety first and only use only one hand on the amplifier when powered and probing about, just to stay alive
What to do for starters though, is locate where those amplifier outputs connect to the relay contacts on the relay-rectifier board and measure any DC volts there. Anything more than say, 100 mV is bad news and anything between say 30-100mV is not a big deal but should be looked into.
A DMM and a couple of small clip leads should suffice for testing at this stage but check out the troubleshooting guide too, for interest, here and locate the power/relay board before taking matters into your own hands - this is not for beginners when things have been messed with already and perhaps left in a poor state. Things to look at are the small timing caps on that board - for some reason they are often the nemesis of simple output protection circuits.
Don't forget the lethal mains potentials around the power supply - safety first and only use only one hand on the amplifier when powered and probing about, just to stay alive
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Several threads on this amp:
http://www.diyaudio.com/forums/solid-state/148403-marantz-250m-repair-6.html#post4958469
Marantz 250 schematic needed
marantz model 250 power amp. Should I fix or make a gainclone out of it
I remember member JBLMAR having a thread where he repaired one only to have it fail again.
http://www.diyaudio.com/forums/solid-state/148403-marantz-250m-repair-6.html#post4958469
Marantz 250 schematic needed
marantz model 250 power amp. Should I fix or make a gainclone out of it
I remember member JBLMAR having a thread where he repaired one only to have it fail again.
Here is jblmar's post ( he did it in my thread):
http://www.diyaudio.com/forums/solid-state/148403-marantz-250m-repair-2.html#post2124958
And here is the failure of his repair - nice that he came back to let us know:
http://www.diyaudio.com/forums/solid-state/148403-marantz-250m-repair-5.html#post2536054
More:
http://www.diyaudio.com/forums/solid-state/148403-marantz-250m-repair-6.html#post4958469
http://www.diyaudio.com/forums/solid-state/148403-marantz-250m-repair-2.html#post2124958
And here is the failure of his repair - nice that he came back to let us know:
http://www.diyaudio.com/forums/solid-state/148403-marantz-250m-repair-5.html#post2536054
More:
http://www.diyaudio.com/forums/solid-state/148403-marantz-250m-repair-6.html#post4958469
Not quite right? Design wise? Interesting...but not surprising from what I’ve read. And it seems par for the course to have channels blown.
This has actually gotten me thinking about a substantial upgrade. Looking at the Ampzilla 2000 or the Audio Research VT-130SE, to pair with my VMPS 626R. But I don’t know...I’m not committed to either.
I’m quite sure the M does not indicate meters or not. I’ve got a 250, with meters.
This has actually gotten me thinking about a substantial upgrade. Looking at the Ampzilla 2000 or the Audio Research VT-130SE, to pair with my VMPS 626R. But I don’t know...I’m not committed to either.
I’m quite sure the M does not indicate meters or not. I’ve got a 250, with meters.
Unfortunately with any forum out there some feel their opinions on design is far better than the engineer that designed a specific make and model. I personally wouldn't walk across the floor for a free Crown product past or present. Others would pump $500 into an old DC150 or 300 and feel they have the best amp available. To each their own.
My opinion based on having owned the Marantz 250 M, 250, and 240 is that its a fine amplifier IF rebuilt correctly. I personally haven't owned one that was 100% working when I purchased it. I have in the past rebuilt everyone that i've owned. They are still working by the way.
There are some that consider the Ampzilla, son of Ampzilla, grandson of ampzilla, SAE 2400, and 2600 to be extremely flawed in their design and yet people still purchase the blown up ones and still repair them, myself included.
Power amps (my opinion here) are generally run hard,abused and mistreated. People terminate them to loads of which the impedance is sometimes below guidelines and expect them to run trouble free for 40 years. It simply doesn't happen. In my 25 years of commercial sound systems I have come to the conclusion that most people are idiots and incapable of the most simple things. Make a system as simple as possible and they will still screw it up. There is no trouble free amplifier everything will fail and when you think you have designed something that might possibly be different it will also go up in a puff of smoke.
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I bought the unit that I have from the original owner, he said that it worked fine for
many years and blew up the first time that he shorted the speaker leads and turned
up the volume.
The design has short circuit protection that does not seem to work.
Have you documented your repair anywhere?
many years and blew up the first time that he shorted the speaker leads and turned
up the volume.
The design has short circuit protection that does not seem to work.
Have you documented your repair anywhere?
Interesting thread:
Marantz 250 & 250M Full Recap | Audiokarma Home Audio Stereo Discussion Forums
Marantz 250 & 250M Full Recap | Audiokarma Home Audio Stereo Discussion Forums
I know this is an old post and I'm a new user, but I was wondering PB2, Do you still have the SPICE file for the 250? If possible I would really like to get my hands on it. I feebly attempted to build one over the weekend and I got stumped quickly and I figure why try and re-invent the wheel.
Thank you in advance.
I did the work about 8-9 years ago and I've gone through about 6 computers looking for
the file but can't seem to find it. I have a few more to try.
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