700M made a sizzle noise....POP....won't power up.

Voltages were measured with everything from the driver boards forward removed. Unit was powered up and checked out fine. Left driver board was installed and powered up, no issue. Left outputs were reconnected and unit powered up, no issue. Right side still disconnected is where we stand. More work to do tonight.


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Yes, brilliant minds think alike- Drummin Daddy, that's pretty much the process we (BK and I) are following. Thanks, all.

I can't wait to get back to the music, rather than hunched over the unit.
 
Thanks for the kind words, but no brilliance here.

If it weren't for EW seeing me through my 700m project, I'd probably be paying someone to do it. :ntwrthy:
 
Three Cheers for Brad a/k/a bktheking!!! Three Cheers for Echowars!!!

Thanks to you both, I now have a working 700M.

Echowars, you are the supreme master of the 700M for a reason, your expertise is impressive and you took to this thread so many times with good advice. Thanks a million.

Brad, thanks for caring enough to spend way too much time on the phone and a bajillion texts, and for being smarter than I am.

Brad patiently guided me through a bunch of tests, and eventually, the process of elimination that resulted in the replacement of the zener diodes on the driver (two on each board is what i replaced). I think the zeners were the problem, but since I stupidly pitched the old ones after putting the new ones in, and good luck trying to find them in the garbage to test them to be sure that was the prob. Anyway, the cyclical clicking of the relays with the dim bulb flashing, seemed to be corrected after the zeners were replaced. Could very well have been that. Dialled the bias in, and was good to go.

I'm now enjoying the music with a recapped 700M, which needless to say, is pretty sweet.

Here's what I did. Replaced the:

two speaker relays; all electrolytics on the driver boards and protection board; all output transistors; all of the transistors on the driver boards and protection board; couple of zener diodes on the drivers; a couple of resistors on the driver; the soft start resistor. And I polished the male connector pins with brass. Think that about covers it.

Gotta say though, those meter needles are really not moving. Gonna look into that, I think I saw a post about that. I have the caps for a meter board recap, might just have to....

Brad, Echowars, may you find an Accuphase amp at a garage sale this weekend for $20. Or a pair of Klipschorns at the curb side. Or a 700C at the Goodwill. Y'know, Audio Karma stuff. AK is the best thanks to guys like you.

Cheers.
 
Happy to help, glad another vintage piece lives and keeps the fire burning!


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I love a happy ending.

(Odd to see an issue with the diodes...don't think I've ever seen a bad one, but I replace them during a rebuild anyway).
 
Been following your thread with a fair amount of anxiety! I am SO glad you got that beaut up and running again! So nice that there are those on here who are willing to share their knowledge and time. Congratulations on having the courage to tackle this project! I know you are going to love this amp all the more for what you went through to save it from the scrap yard.
 
I love a happy ending.

(Odd to see an issue with the diodes...don't think I've ever seen a bad one, but I replace them during a rebuild anyway).

It may not have been the diodes. But, I disconnected and reconnected the boards, and changed the diodes around the same time. As BK can attest, we thoroughly checked all of the plug-ins and transistor/cap orientations. Like, quadruple checked. So, what magically corrected the problem, is really hard to say.

But, it works. And sounds great. Love the 700M, and once I get the meters perking up, it'll be even better.

Attached are pics of a driver board before and after, protection board after, and parts removed, missing only a very few parts that made it into the garbage and didn't make the group photo. Note, I didn't replace the soft start relay on the protection board, just to save a few bucks. But maybe some day I will.

Note also, I've only recapped one amp before- a Marantz 2270. Not only does the 700M kill the Marantz in terms of sound, but it was a lot easier to recap. The 700M is not that difficult. There's a fair amount of space in there, and getting the boards out is a total cake walk, due to the plug system and easy extraction overall, vs. desoldering connections (major pain with the marantz). Notwithstanding the times when I was banging my head against a wall, the project was pretty easy and fun.
 

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  • Parts removed.jpg
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  • Protection board AFTER.jpg
    Protection board AFTER.jpg
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