Disassembling Marantz 4270?

ViperZ

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Hi all, I am stuck a bit. I worked on my smaller Marantz receivers before (mainly 2250 and 2238), but this one is just stuffed inside that small case.

I have some electrolytic caps visibly leaking on the power supply board, so now the voltages that go to the protection board seem too low and relay coils buzz (and barely close contacts).

Is there an easy way to unscrew that board without removing the right amplifier board beside it? I can't get to to the bottom bolts that hold the little heatsink on the side (tuner cover blocks those).

Thanks!
 
Yes the power supply can be removed without pulling the amp module. All the screws are accessible. I would use a long magnetic tip screwdriver so you don't loose them. You will need to unsolder some wire posts to get it out though.
 
Thank you very much, bryans12v! I took the screws out. Definitely looks like I will have to take some wires off one side. They are wound around the pins. Should I just desolder the pins from the board?

I was going to start measuring the output voltages, but the board needs repair and cleanup even before that. Someone replaced 3 electrolytic caps on the board, but did not clean leaked out electrolyte. It rusted transistor and resistor leads, and probably partially shorted H801/802/803 transistor leads. Hopefully I can clean it out without replacing those transistors.
 
I like to un-solder the pins. it makes it look like you never touched it.
No matter how good i think i can solder, it never looks good to me.
 
I desoldered 4 pins on one side, so now I'm able to work on this board. Very unfortunately, someone else tried to repair or "repaired" this board before me. Giant blobs of solder hanging on the leads, burned up traces and a couple of pads almost falling off. Took me about an hour to remove all electrolytic caps (there are like only 8 total) and 1 resistor, which got dissolved by the electrolyte (the resistor itself was ok, the ceramic coating fell off when I touched it).

I'll put it back together and hopefully start measuring voltages tonight. I'll do whatever it takes to fix this 4270, as I intend to keep it for many years.
 
A quick update. I did more work than expected (with a 3-year-old kid in the house) today. Rebuilt the power supply (new electrolytic caps, 1 new resistor, fixed some traces, washed the whole board to clean the electrolyte.

Now the power supply works, both relays click. Both power amp channels work.... Only right channel works out of the preamp. Looks like some buttons are dirty. When I first turned it on, both channels were dead, I pushed 'source' button a few times and right channel came full strength. Left channel is very weak. I guess, more disassembly and clean-up of pots and buttons is in order...

IMG_20170108_170648.jpg
 
I am assuming that you did the cris-crossing your Pre/Main jumpers with a harness. just in case the jacks are dirty.
Id bet its something simple like a tape monitor or some other switch. Otherwise check connections to the pre amp, if it plugs in, and make sure the contacts are clean, and also check the solder joints real good on that board. Its not an amp issue. Thats good.
 
Yeah, I connected another receiver (with removed jumpers). Both channels were playing fine with external pre. When I connected them the other way (Marantz being pre), the left channel was mute. I didn't try this with rear channels, but amp board is definitely not a culprit.

I spent last two hours learning the schematics and tracing the signals, and still have no idea where the front-left signal gets lost. Oh yeah, rear-left works fully when matrixed (4-channel switch on the back enabled). And that's exactly what I see tracing the signal through preamp boards - there is no signal going through front-left channel. All 4 channels are identical, so it's easy to compare them to each other.

I bathed all accessible pots (volume, source) in deoxit (gotta wait for it to dry out now). I can't get to the buttons without full disassembly (i.e. hi-filter, loudness, or even tape/source). I tried working all other buttons and pots, but there is zero effect on the front-left.

Also tried local/remote switch on the back. 'Remote' puts both channels at equal low volume (assuming need external wired remote control). 'Local' again turns on the right channel, and completely turns off the left channel (meaning the signal is not even getting to that switch either).
 
On mine, the two buttons vertical on the far left were the culprits, tape1/tape2 and tape/source. Hard to clean but removing the left side wing gives some access. Also, I had one that had no output until I cleaned the remote/local with de-oxit. Good luck Rich
 
On mine, the two buttons vertical on the far left were the culprits, tape1/tape2 and tape/source. Hard to clean but removing the left side wing gives some access. Also, I had one that had no output until I cleaned the remote/local with de-oxit. Good luck Rich

Thank you, Rich. It does seem that tape/source button or remote/local switches can be the problem. By wing you mean that piece of metal blocking the buttons? I didn't realize I could remove it. It's just weird that there is absolutely no sound coming through the channel in that one configuration, so it must be really dirty. But on the other hand that tape/source button was the problem for the right channel, so it may be just worse for the left.
 
OK, I am not very good with the way Marantz draws their switches. My understanding is that I have a bunch of sources being switched by the source selector, but then the output of this switch goes to the tape/source switch. So if I put signal into 'tape 1' input, then basically, I am selecting between 'tape 1' and everything else by pushing that button. I do not understand why the output of that tape/source switch goes back to the source selector as another source (tape 1).

Doesn't make any difference though - I put signal into 'tape 1' input, I get no left output. I put signal into aux/cd input, no left output. So does it mean my source/tape button switch is broken, or is it a selector switch, or I am totally out to lunch?

I removed the left 'wing' metal bracket to get access to those 2 buttons (tape/source and tape1/tape2), but I still don't see where I can apply deoxit (still don't see the end of the tape/source switch - it's very long.
 
Those switches can be troublesome.
I've seen some where the end of the top cover was broken off to get access to get cleaner in them.

When I can get at switches like that, I drill holes in the end of the cover to get cleaner in them.
 
I was able to un-screw the bracket holding the switches and tilt it out enough to get to the switches. You can also inject de-oxit into the front of the switch while it is still mounted. Rich
 
I tried that, but something must have fallen into the switch, it wouldn't operate after I drilled it. I shy away from putting a hole in the switch if I can.

Make sure the switch is "out" and try not to "stab" through with the drill bit.

It's a trick.
 
OK, so I'll try the unscrewing bracket method first when I'll get home. I believe more disassembly of the front plate is required :).

One other thing I found was that a previous guru who worked on this unit replaced the receiver feet. It was all good until I saw that the bolts they used are 3 times! longer than the original ones (lucky me I had a few bolts laying around to replace those). Rear ones are OK - they went straight into the heatsinks. One front one barely missed the headphone jack assembly. The 4th one hit the tape1/tape2 switch head-on and bent one pin completely down. Lucky me it was not a functional pin, as there were no wires on it, and it's a simple switch, unlike tape/source switch just above it.
 
Those feet screws can take out channels in some models by grounding out the signal pins on the backs of the jacks. I assume you remedied this and still had the issue. I'll throw in that the local/remote switches are real buggers to get cleaned fully. Do a DeOxit treatment and repeat after at least a couple of hours or better yet overnight or longer.

It is tough to try and follow the schematics on most any Marantz model, especially the rotary switch ones. Horrid, really!
 
I was able to un-screw the bracket holding the switches and tilt it out enough to get to the switches. You can also inject de-oxit into the front of the switch while it is still mounted. Rich
I found a piece of brown phenolic in the switch area on disassembly. Any idea what that goes to? I took a picture, but it is not helping me.
 
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