4270 crosstalk, recap?

N8Nagel

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Hi all,

well sure enough I got a huge package in the mail today; it wasn't as big as my Sansui QRX-7001 but damn close to it. It was my friend's old Marantz 4270, he just is giving up on it. He complained that it was all crackly and didn't work unless you cranked the volume, well it looks like nobody ever cleaned the 70s man cave out of it, so I Deoxited the hell out of the pots and sliders and at the same time dunked the knobs and face in the sink. So far so good, at least on headphones - so I guess that means if the headphones work but I have issues with the speakers at low volume, it's going to be related to the relays.

But here's the thing. If I plug the headphones into the rear jack, even in 2 channel mode, I have a significant signal on LR. Looking in the unit from the underside, there is a small board that connects to the "power mode" switch and it looks like the largest capacitor on that board done blowed up. It's still there, but wobbly and bulgy. So I'm guessing the repairs should start there. Given the issue that I mentioned, are there any other areas that I should be looking at, or basically just start at the power mode switch and methodically recap each board until it works right?

Edit: after downloading the manual, it appears to be "B.T.L Phase Inverter Assembly PM01" and the blowed up cap is CM05.

This is going to be a back burner project as I need another quad unit like a hole in my head, but at the same time it's got too much potential to just shrug and give up on, or run knowing it has issues and possibly blow it up. If the hive mind thinks there's a chance that recapping just that one board will bring it back to proper operation I'm willing to try it... need an excuse to order from Mouser anyway.

Also, question: my 2220B had nice stainless hex head machine screws holding the face on, but this looks to have (used to be) chrome plated regular old JIS screws. Is that correct for this model?
 
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Screws are the same as your 2220b, it's a nice quad unit well worth the effort ... oh and don't switch the stereo/quad switch with the power on.
4270_final.jpg

Good luck! Rich
 
nice looking unit. "Mine" doesn't have the wood case though just the metal one. I actually knew about the switch thing, I'm wondering if that might be what happened. Unit is filthy inside but sounds good... except for the crosstalk issue.

Guess I'll start making another parts list, unless someone's already done it for me. I should probably test the tuner with an antenna as well, although I don't know what I'll do if it doesn't work properly as I don't have the tools or skills to align one.
 
Nice units when working well.

One hell-on amount of electrolytic caps and tantalum caps everywhere.
The power supply get worked hard, recap.
The Dolby can cause noise even when off, recap.
The tone board has tantalum hiding deep inside, must split the mother/daughter boards to re-cap, recap.
The pre-amp board is right there when you do the tone board, lots of caps, re-cap.
The speaker relays are on the back panel, they can get dirty, service or replace them.
The Dolby pots under the meters are hell to get at to clean, clean them.
The tape switches on the left get wonky, hell to get to and clean, should be cleaned. (drill holes in the back cover of the switch if you can).
Need to unhook a lot to do the power supply and you should re-cap the amps so recap them while you have the power supply loose.

Then, if you get bored, re-capping the MPX is best done while the amp is out.
If you go for the MPX, you may as well to a AM while there.

Once you go that far, may as well throw in new main filter caps.

THEN we'll see how it does.....
 
Wow, you make this sound so easy to work on :)

sounds like you've done this before, you don't happen to have a parts list ready to go so I can just place an order with Mouser or Digi-Key do you?

Are there any of the notorious "noisy transistors" in this guy? I saw a couple that looked suspect on the board with the suspect cap, but they weren't 458s and I don't have the list memorized.

Are the trimmers pretty good on these or should they be replaced on a board by board basis as well?

Supposedly my caps for my Scott project will be here tomorrow afternoon so I might actually get to this (assuming that I don't tackle my Pilot 654 next) Don't really need another quad unit, especially one without a SQ decoder, but what the heck.
 
I've rebuilt a few.
http://audiokarma.org/forums/index.php?threads/marantz-4270-restore.717926/
http://audiokarma.org/forums/index.php?threads/another-4270-under-the-knife.535976/

No I don't have a list, I have a room full of parts.
I don't think Marantz used noisy transistors, just miss-labeled the boards.
Trimmer on Marantz are usually good. The only bad trimmer I ever found was on a 4270 though but THAT one had about everything mucked up (second thread).

Its a good solid week of work to rebuild one.
 
I think I am going to do a "partial" before putting this back on the project pile, at least recap the PM01 board (because one of the caps is quite clearly bad) and the power supply board (because every thread I've seen on this unit says "the power supply is stressed") because I'm just hopeful that fixing the PM01 board might restore proper operation. I did check DC offset and it's quite good, and runs cool. Hooked up bench speakers last night and let it run for a couple hours, other than a few light bulbs and the crosstalk issue, not bad.

Do I need to uprate the voltage ratings of all caps like I would for tube gear or is this new enough that exact match is OK?
 
I think I am going to do a "partial" before putting this back on the project pile, at least recap the PM01 board (because one of the caps is quite clearly bad) and the power supply board (because every thread I've seen on this unit says "the power supply is stressed") because I'm just hopeful that fixing the PM01 board might restore proper operation. I did check DC offset and it's quite good, and runs cool. Hooked up bench speakers last night and let it run for a couple hours, other than a few light bulbs and the crosstalk issue, not bad.

Do I need to uprate the voltage ratings of all caps like I would for tube gear or is this new enough that exact match is OK?

Going up in voltage is fine if you have the room for it. This is always something to watch out for, particularly in quads where everything is packed in tightly. You will have to measure width and height on the caps that are very close to resistor legs and other components. The four electrolytic caps on the tone board sit right up against another so you have to use caps that will fit. Local filtering cap on the dolby board will need a close eye on size also.

Generally new caps are smaller than the ones you are replacing but Silmics run fairly large when upping the voltage. Usually I find that going up one voltage level with Silmics almost always is the same size as what's coming out. I have a look at my order history for the 4270 order to see if I can get you a good list if you like using silmics.
 
I don't know what I "like" as I'm really just starting to get into repairs, however I was planning on using Silmics for the phase inverter board as that seems to be what most people do, and I am assuming that those are in fact in the signal path (all are orange Elna "CERB" save for one completely unlabeled lavender one - the latter being the one that blew up - and based on what limited info I can find, the orange CERB caps are low leakage type) any other suggestions welcome

I need apparently four 3.3 uF/50V and one 100uF/35V to rebuild that board. I haven't made a list yet for the power supply but based on previous comments it might be good to have those parts on hand.

The more I think about it though the more I'm darn near 100% certain that it's the phase inverter board that is causing the weird crosstalk issue, unless something is miswired/shorted somewhere.

There are also two 2SC1345(D) and two 2SA763(4,5) transistors on that board. I'd like to have replacements on hand for those as well just in case, although I don't anticipate actually needing to replace them. Suggestions for replacements? (what do the (D) and (4,5) mean anyway?)

Really don't have much to do but obsess about this as the can caps for my Scott receiver that I was hoping would show up yesterday didn't, so I'm working on a parts order to hopefully fix this Marantz instead of actually fixing stuff...

thanks...

Edit: If anyone has a scan of the entire schematic, not chopped up like it is on HFE I'd appreciate it! Alternately, if someone has an original manual, I do have the ability to do large format scanning if you trust me enough to unstaple/restaple it.
 
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As Brian wisely stated, be observant of the diameter of your replacement caps

If they are 4.7uf, then you can also put polypropylene films in, if you have them. they are not cheap though.

The D, Stands for the HFE rating. On your 2sc1345, it is 250-500
512-KSA992FBU will replace your 2sa763
Fairchild KSC1845FTA will replace the 2sc1345
These should both be ECB layouts, but never take that for granted.
Its important to match hfe on each stage. The first stage, (diff pair) of you amp circuit is critical. Buy twenty of each and check/pair the matching ones.
 
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OK so I gave up putting together a whole list of parts for this and just rebuilt the BTL phase inverter board

Good news: the caps I got I guessed right on the lead spacing. The 3.3 microfarad ones are kind of big though (silmic) in diamater, if I do recap the rest of this thing there are places those just won't work, need to find a better replacement.

More good news: Crosstalk on rear channels is gone. Works great in two channel mode.

Bad news: No right rear channel, was working before.

Does the signal travel through the BTL phase inverter board? There was one of the 3.3s I lifted a pad removing and I thought I scraped enough of the trace and got enough solder on it to be good, but that's the only thing I can possibly think of that I did that was questionable. Or is it possible that there was another fault that was masked by the bad board (the 100 microfarad cap wasn't even connected, the + lead was corroded completely through) Odd thing is though I have a tone probe (half of an electrician's fox and hound, actually really handy) and get no signal at any of the wires going into that board although obviously I have sound on three channels.

I ended up not ordering transistors as I have no ability to measure hFE.

What blows up when you change the power mode switch with the thing powered up? Is it possible that I screwed up and should have ordered those transistors?

Any advice appreciated. This is really my first stab at a real repair so be gentle :)

thanks much

I did take pics so when I get this all sorted I can post them
 
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It was bugging me so much I desoldered the amp power wires again and pulled the board, meters out good. I did find one pad near the big cap where I'd apparently inadvertently sucked the solder out from around a lead and got all excited... nope, still got three channel sound.

Any ideas where to look next would be appreciated.
 
3.3uf silmics are tough to find under 100v. For these i would use 50v nichicon fine golds or UKL series.

Try giving the pre out main in jacks a good cleaning as well as the 2x4 switch on the back. The 2x4 switch contact plates should be examined with a bright flashlight. All that black crud should be removed with alcohol and qtip.

If that doesn't solve it, check for a separates wire. Those bottom boards have to be moved around a lot to get to the foil side, wires can easily break off the posts.
 
Already did a deep clean when I first got it. Was getting sound out of both rear channels before, I haven't a clue what I may have boned up here. Or did I? I can say that other than a little crosstalk in the LR that the faders all seemed to work correctly making me think the issue is not in the preamp section.

Thanks for the recommends on the caps. Yes I used 100V Silmics and all were larger in diameter than the ones they replaced. I now have confirmation on the lead spacing though so I can order better replacements should I decide to go whole hog.

Edit: I should also mention that I am using the headphone jacks right now for testing if it makes a difference. Haven't hooked up actual speakers yet.
 
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Update: I had the idea to remove the rear pre out/main in jumpers and feed a stereo signal straight into the rear amps from my phone. I get good sound on both rear channels that way, but ONLY if I have the power mode switch in 25Wx4 mode, which I assume is correct behavior yes?

What this says to me is that apparently the amps and the BTL phase inverter board are good, yes? If I'm reading the schematic correctly the phase inverter board is AFTER the main in jacks correct? Meaning that I had two faults and one of them is upstream of the pre out jacks. To verity I left the jumpers out, put phone back on Tape 1 rear channel inputs, and measured voltage at the pre outs, I get a twitchy needle on LR but nothing on RR.

I am wondering if the main/remote switch is messed up. I remember having to work it a bunch of times and flush it a lot to get sound when I got this thing. Only way I know to confirm though is to find the other end of where the RR channel signal enters that switch and without a good schematic I'm kind of lost. Any suggestions where I could find one that isn't all chopped up?

Anyway if you could please confirm I'm thinking right, there has to be another fault in the preamp section that is dropping the RR signal somewhere that was being masked by the bad BTL phase inverter board and now that I've fixed that I have at least one more fault to track down. correct? I just can't imagine that this fault existed before because I distinctly remember the rear balance fader working sort-of correctly before (although the LR would never go dead silent and now it does) and now I have absolutely no signal on RR.
 
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