Marantz 1200 from HELL!!

IT LIVES!!!!! (But......)

Got my 1N5356B zener in from Mouser earlier in the week; installed it and wired everything back up this weekend. Brought it up on the DBT and after five seconds or so, heard one of my favorite sounds in the world - that lovely relay click!

Plugged it in without the DBT and had no problem setting bias and offset, so I figured I was in pretty good shape. I hooked up an iPod to the AUX1 in and I sat there for a minute wondering how many years it had been since the last time this amp actually worked. I've owned it for approximately three years, and it had been so badly scrambled that I doubt it's been functional since well before the turn of the century/millennium.

As I was testing all the functions and putting her through her paces, I noticed a weird problem, though. Any input into AUX1/AUX2/TUNER could be heard loud and clear when the input selector was switched to PHONO1, PHONO2, or MIC. In other words, any high-level input signal can be heard whenever any low-level input is selected!

I poked around a bit, but couldn't find anything obvious. I guess whoever futzed with the amp boards must've also done a little creative rewiring in the preamp or selector circuitry as well. Looks like I get to tear everything down one more time and start signal tracing.... :gigglemad

There were several service bulletins on this amp to address cross-talk issues.
Maybe one of them was performed improperly.
You can find them in the AK database at the end of the (incomplete) service manual.
I have tried to upload the complete manual, but the file is rejected due to it's over 20MB size.

Tom

catrafter said:

I have tried to upload the complete manual, but the file is rejected due to it's over 20MB size.

Click to expand...

Why not split it in half, and upload it as "part 1" and "part 2"?

To the OP: helluva job fixing that mess. I thought the inside of my flame-ball 2235B was bad...

catrafter said:

There were several service bulletins on this amp to address cross-talk issues.
Maybe one of them was performed improperly.
You can find them in the AK database at the end of the (incomplete) service manual.

Tom

Click to expand...

Thanks, Tom! Perhaps what I'm seeing is an uncorrected factory issue. I'll check the bulletins and see where they take me...

(BTW, I recently uploaded first and second addendums to the Marantz 250 SM - VERY useful for anyone working on a 250, or on 1200/1200B amp modules!)

Sam Cogley said:

Why not split it in half, and upload it as "part 1" and "part 2"?

To the OP: helluva job fixing that mess. I thought the inside of my flame-ball 2235B was bad...

Click to expand...

Good idea, I think I have a PDF splitter somewhere.

Tom

skibjr said:

Nothing like soldering new transistors to the chopped off leads of the old ones. I mean, why waste the five whole minutes it might take to properly pull the driver board? Some nice work done on the circuit side of the relay board as well...

Finally, the last shot is a little tantalum cap that was connected between the shielded side of one of the "Amp In" connectors and ground - probably to block DC from the preamp section. Looks like it took a few volts, huh?

Well, that's it for the "before" pics. "After" pics to follow in a little while...

Click to expand...

the transistor thing I've seen in the field off and on. usually it comes from popular shops that are just too busy to do it correctly ( I had to fix a lot of crap like that that came in from some snooty audiophile shop and the customer was unhappy with their repairs. Usually, I show them what butchery they have done and most of the time those customers come back to me for other services.)

that cap doesn't blow up unless they caused a ground loop. usually its from hooking the amp directly to a cheap modern TV.

The blob of capacitorness might be a mod for that type of amp.

But if you want my opinion, you should get another one and use this one for parts or vise-versa and match those output amp boards so there the same revision.

Just have to ask, where on earth does that light bulb go in the 4th pic on post #12. Looks pretty tight in there for such extravagant on/off indicator illumination to me ---- j/k

Nice rescue.

Those before-and-after pics are like seeing pics of a carnage-strewn battlefield at the end of a hard-fought battle, and the well-manicured memorial park lawn at the same site, decades later. Nicely done restoration work! :thmbsp:

I have a 1200, which fortunately hadn't been so hacked up when I got it, but I've seen some other "horror story" cases like that. Always a very sad thing to see. Some people should be banned for life from opening an audio-gear case or hoisting a soldering iron!

At long last......SUCCESS!!

A big thanks to catrafter for cracking the crosstalk problem I was having! It was indeed a factory wiring issue, and I would have pulled my hair out trying to figure it out without the service bulletins Tom referred me to on the AK database.

Interestingly, there were three bulletins addressing this issue, each superceding the previous one. Naturally, I applied the last one first, involving jumpering two terminals on the selector switch, then wiring the new jumper to ground. It didn't work. So, I went back to the previous bulletin which advocated removing three factory-installed jumpers from the selector switch. That fixed the crosstalk. :yes:

Figured I was finally done, but I thought I'd do a final once-over before I sewed her up. Everything checked out perfectly - until I slid the rear gain switch to "Low" - at which point I lost most of my left channel. :dammit:

I traced the switch connections to the front panel circuit board, and tried to check the connections to the attenuating resistors mounted there, but I couldn't get at the damn things, so once again, off with the dozen or so fasteners required to pull the front panel, pull the front-end preamp, tone & phono boards, finally get a flashlight in there to take a look. I ended up finding close to a dozen bad solder joints, most of them where the panel-mounted controls connected to the PC board (see pic below). After seeing how many connections like this there actually were, I was amazed the preamp section worked at all!

I repaired all the bad joints, took special care to resolder the attenuator resistors, and touched up about a dozen other joints just for good measure. Put it all back together, cooked it for about an hour, and she ran like a charm. I reset the idle current and DC offset, cleaned up the knobs and faceplate, and completed the final reassembly. I've included a final shot, showing her in all her glory. The 1200 is a phenomenal amplifier - with that nice warm "Marantz" sound, and a real looker, to boot. A few months of work, and she had me scratching my head a few times, but I think the effort was well worth it! :thmbsp:

Kudos! Reminds me of 'bad amplifier' days I had in the service business. There is a great sense of accomplishment when it's over, but customers will never pay for the full value of this effort. You have to do it for love.