early eighties Marantz PM-750 DC

sorry the trouble Bert I made your changes but 'the leds of the equalizer light up all together as in your picture at the end
 
So it's not working at all ? Does the relay click after power on ? Any sound at all ?
I just came back after being away for a week. If you want to be sure that I read your posts also write in the discussion, il get an email alert.
 
Working on one of these now.

Did you end up replacing the fusibles in the power supply with fusibles or just standard resistors?

The four in the power supply here are toast. Reading between 3k-7k! I have standard fuses here but wondering why they specifically used fusibles.
 
@bryans12v
I used standard resistors, my 750dc is sometimes in use in my system and sounds great!
As for why they used fusible resistors, my only guess is safety?
 
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I was just rereading this threat. Wow, there was a lotta love that went into that restoration. Good job. I always regret not restoring a Sanyo I once had of that era. It was an amazing sounding stereo. But I was too pig headed to accept that it was truly worthy of a restoration. It met an unfortunate and undeserved end by my hand. A choice I regret to this day.

Good luck and enjoy
 
I've just recapped and cleaned up one of the PM-750 DC's baby brothers, a PM450. Again the build quality is excellent although the design is admittedly not to everyone's taste. What's really surprised is is the huge improvement in performance that the recap has made.

My previous project was a 1050 from roughly the same era which saw a notable improvement in sound quality post-recap, however using similar components on the PM450 and it's like a completely different and much higher specification amplifier.

I initially assumed that the old caps from the PM450 were much more degraded than those in the 1050 but nothing really showed up when measuring values of the components that had been removed.

Bit of a head scratcher really why one amp was so dramatically improved compared to the other. Either way, I'm please with the results from both exercises.
 
Funny that this thread recently had more comments as I just started working on a PM750DC and had been referring to it. I liked the PM750DC so much I just bought another one but the new one is a US voltage only, not the multi voltage version. I didn’t expect differences but so far things of note are a hard wired power cord, a standard size fuse with finger threaded cap instead of mini fuse and screwdriver needed cap, and gold plated RCA jacks instead of nickel.

If I find many more differences once I open it up I may start another thread on the subject. There’s just not much info out there.

Thanks for documenting this rebuild. :thumbsup:

Mike
 
Here is my list, my order was from Mouser, total was 75 chf which is about 75 usd or 65 eur.
Dear Bert 1100, don't know if you still read this forum but thanks for you PM750 DC "Rescue".
I did the same job on mine, it was working, not defective, but forgotten in the garage because of a loss of interest and not-so-good sound compared to an old Sansui AU217.
Recapping the unit changed a lot this amp, especially on the low end ( power supply surely ).

I did something more that may be of some interest : just for fun , I put a DIP 8 support for the 4558 AOP on the driver stage, and tested the results with several other amps, as the design allows it : NE5532, OPA 2134, OPA627....

I checked with good headphones and the noise level is quite reduced.
The best uprgade regarding sound upgrade seems to be OPA627, mediums are softer, highs are great, but anyway each tested AOP fitted there is worthwile and quite better than this old 4558.


This amp, now fitted with new banana terminals for speaker 1 set definitely sounds better ! i can post some photos if someone is interested.

Thanks again Bert for posting your nice work!.

Regards.

Nicolas
 
Hello @Bert 1100 , i just check the capacitor brand name is Onkyo instead of Marcon like yours? Maybe previous owner recap it? Or maybe manufaturing for different markjet have different caps?
 
More pics :D

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It's pushing 24.5 Volts on 8 Ohm at 1kHz, both channels working, giving 75 WPC before clipping.
The manual gives it at 80 WPC, my guess is that this is with one channel at a time ?
Also, I've set the mains voltage for 240VAC, when my line voltage is 230 - 235 VAC...

So, what's not to like about this amp ? Construction is not bad, still all metal, the looks I like, the sound I like very much, and the price was a bargain !

Is it at volume value 35-40 that clipping?
 
Hello, new here, stumbled upon this while looking for a rebuild kit for my 750DC. Back in the early 80s I had this unit, used it up until I lost it in a fire back in 2000. I found a unit on eBay, seller said it worked, so I got it. Well, it didn't work. The safety relay wasn't engaging, so I knew from my shop experience the first target was to check the finals. Sure enough, one pair is overheating and indicated the shorted pair. Lifted the legs of the transistor from the board on that bad channel, and relay kicks on and I have one channel sound. I ordered a pair for both channels and now it's working like I remember. Being an old unit, I figured some refreshing is warranted, so that's where I'm at. So glad I stumbled onto this thread!
 
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