Marantz 2270 Left Channel Distortion when PHONO is selected.

[SpencerR]

Hi, I'm having a bit of trouble with my Marantz 2270. Everything works flawlessly except for an intermittent issue I've been having when the "PHONO" input is selected- when "PHONO 1" or "PHONO 2" is selected, the left channel is somewhat distorted and choppy. The audio never actually fully cuts out, however; even when the turntable is not spinning a record, an audible white noise type of static can be heard. To troubleshoot the issue, I've tried several things in order to find out what exactly may be causing the issue.

• It is ONLY affecting the "Phono 1" and "Phono 2" inputs, as all the other inputs on the 2270 work fine and are clear.
  
• It is not the turntable- I have another turntable, and after hooking it up, it does the same exact thing. I know the turntables are in perfect working order as I have other receivers available to me and I tested them with those receivers and they work fine. The cartridges are fine as well, and it's not a groundwire hum situation either.
  
• It is not the speakers- not only do they work perfectly on all the other inputs, but the speakers I'm using work fine with other receivers, and after hooking up different speakers to the 2270, the issue still is the same.
  
• Even when switching the L cable output from the turntable and putting it into the R input and vice versa the issue still persists.
  
• When I select the "R MONO" on the 2270 the issue goes away. This takes the signal from the right channel of the turntable, makes it mono, and puts it out both speakers. Sound is clear this way, making me think it affects the L channel on the board.
  
• It's not the actual jacks in the back, because they produce a clean sound when I select "R MONO" like I just said.
  
• It was brought into a repair tech who took a look at it, cleaned it, tested it, and used tools that said there was a strong signal on both sides... but, it's back home now and the issue is still here. Like I said, it's intermittent so maybe he wasn't catching it. It happens around 50-60% of the time, but it drives me absolutely nuts when it happens.

Am I correct in assuming the issue is isolated to the phono board, and particularly to the left channel? Or is it something else? There's not much else I could think it would be, as I've done pretty much everything to find out what the problem is.

Thanks in advance.

 

[JURB]

High value resistors in the phono preamp. nything over 47K. In fact just pick the highest values and replace, and if it isn't fixed replace the lower value ones, and then lower and then lower if necessary.

That is the most logical way to proceeed. the high value resistor have more tendency to go open and they are used for bias alot./ you got distortion right ?

We are not talking bad frequencty response right ? Some people don't know the difference. Disrortion is whe you play an electric guitar. Noise is sound when you play nothing. Some people call a screwed up frequency response distortion and I have to admit ithat it really is, but we cannot define it that way here.

Question, does this effect fade in and out or just come and go like immediately ? It may matter.

Anyway, one other thing is that you should probably pull out the phono board and at least look at it for bad solder connections. You might just find the problem by visual inspection.

 

[skibjr]

Probably the phono board, but if you haven't Deoxit-ed your selector switch, now might be a good time. Does your phono board still have the original 2SC458 transistors? These are perhaps the most failure prone transistors ever manufactured, and the first thing I would check. Marantz even published a service bulletin advising techs to proactively replace these on all 2270's that came in for service. If you have 2SC458's in there, replace them with 512-KSC1845FTA from Mouser before you do anything else.

 

[rBuckner]

I totally agree with 'skibjr'. I'd also replace the diodes that look like epoxy blobs with thin leads. There is one by the two adjustment pots which can be replaced with two 1N4148 or 1N4448 diodes in series. There are two others closer to those rotten C458 transistors and those can be replaced with a single 1N4148 diode.

Yes resistors can go noisy but I've never seen one do it in a Marantz anywhere. I bet it's better by the time the semiconductors are changed out.

 

[SpencerR]

High value resistors in the phono preamp. nything over 47K. In fact just pick the highest values and replace, and if it isn't fixed replace the lower value ones, and then lower and then lower if necessary.

That is the most logical way to proceeed. the high value resistor have more tendency to go open and they are used for bias alot./ you got distortion right ?

We are not talking bad frequencty response right ? Some people don't know the difference. Disrortion is whe you play an electric guitar. Noise is sound when you play nothing. Some people call a screwed up frequency response distortion and I have to admit ithat it really is, but we cannot define it that way here.

Question, does this effect fade in and out or just come and go like immediately ? It may matter.

Anyway, one other thing is that you should probably pull out the phono board and at least look at it for bad solder connections. You might just find the problem by visual inspection.

Hi, and thanks for your response. I'm fairly certain it's not frequency distortion. And yes, there is distortion, however, there is also a white noise when the turntable is not playing.

To answer your question, the effect does not fade in or out, it just comes and goes. Sometimes I turn the 2270 on and it has the issue, other times it will be fine. Also, when I'm listening to the turntable sometimes I'll notice it, even when it wasn't there when I started listening.

I think I'm just going to bring it back to the repair tech, who said he will take a much closer look at it, and is confident he can repair it. I sure hope he's able to. I think he should replace the board as a whole, but if he thinks he can repair the board itself, then I think that's okay right? Unless he should just swap out the board.

 

[rBuckner]

I'd only replace the board if the board itself was trashed from poor soldering. You're not going to get a new one anymore for sure so only used is out there. You've received very specific info on what is a proven way to fix or prevent many issues on this board, please pass that on to the tech. One more thing to add is to have any tantalum caps on there replaced with nice audio grade electrolytics.

 

[kirkendoll]

I was gifting a realistic receiver and a turntable to a friend and it did exactly the same thing on one channel after I set it up in his house

 

[Bunty2]

I'd only replace the board if the board itself was trashed from poor soldering. You're not going to get a new one anymore for sure so only used is out there.

Aren't there any companies out there that make new circuit boards off of patterns provided in the service manual?

 

[rBuckner]

That would be an expensive proposition to have them scan it in and recreate artwork but I bet it could be done. It'd be easier to redraw it in a CAD program and create the necessary gerber files. Then there's the expense of making a small batch.