Marantz 2235b - Intermittent Dead Channel

[GnarlyBus]

I've had my Marantz for about 6 months. When I got it, I put LEDs in, replaced the vellum paper and DeOxited all switches and knobs. Lately it has started to have an intermittent dead left channel. It is not a dirty switch. When I use the preamp outs to hookup another amp it doesn't happen (so the issue is in the amplifier section?). If I turn the receiver off and on again, the channel comes back for a while. If I run the volume knob up really high, it comes back for a while even after turning it back down.

Any ideas?

I know how to use a soldering iron and I've done re-caps but I haven't done anything to this unit.

 

[Ray Gianelli]

I've had my Marantz for about 6 months. When I got it, I put LEDs in, replaced the vellum paper and DeOxited all switches and knobs. Lately it has started to have an intermittent dead left channel. It is not a dirty switch. When I use the preamp outs to hookup another amp it doesn't happen (so the issue is in the amplifier section?). If I turn the receiver off and on again, the channel comes back for a while. If I run the volume knob up really high, it comes back for a while even after turning it back down.

Any ideas?

I know how to use a soldering iron and I've done re-caps but I haven't done anything to this unit.

Try tapping on the protect relay when this occurs. If the sound returns to the dead channel replace the relay.

 

[GnarlyBus]

I'll try that. Just gotta wait for the issue to present itself again. I'll report back after trying. Thanks!

 

[cademan]

Yup, sure sounds like dirty relay contacts.

 

[GnarlyBus]

The dead channel happened again so I tapped the relay and nothing happened. I checked the contacts visually and they look to be making a good connection. They look clean to my eyes.

When I turned the power off and on again, the channel would come on (after the relay clicked) and then drop in volume until gone again over a few seconds. It did this every time I turned it off and on.

 

[ivandezande]

The dead channel happened again so I tapped the relay and nothing happened. I checked the contacts visually and they look to be making a good connection. They look clean to my eyes.

When I turned the power off and on again, the channel would come on (after the relay clicked) and then drop in volume until gone again over a few seconds. It did this every time I turned it off and on.

If it's not the relay, not a connection, not a switch or control, you're in for some fun. Start poking around with something plastic, get some freeze spray, inspect solder joints.

 

[GnarlyBus]

Ok, I'll set it on the bench and see what I can find. I'll start by taking a closer look at the amplifier board.

 

[GnarlyBus]

I always appreciate when someone finishes their thread by providing the solution. Here's what I did:

I did a re-cap of the PE01, 400, 700 and 800 boards plus new filter caps and relay. Here's a link to the kit I used. I chose it because they use the wima stacked film caps I've read so much about. Plus Bourns Trimmer Pots! https://www.ebay.com/itm/313307090397

The kit included some transistors as well. It really wasn't too tough. If you haven't ever re-capped something and you're reading this...learn to solder well (watch videos and practice) before trying to do this. I'd also recommend skipping the cheap soldering irons I started with and go straight for a Hakko or nicer.

After re-capping, I followed the audio adjustment instructions in the service manual using this video as a general tutorial:

I wasn't sure if it would fix the issue, but so far so good after hours of listening. We'll see if it comes back.

The sound is improved maybe about 10%. It sounded excellent before but it does seem to have a little more clarity. So the Sansui 5000a is going back to storage. I love Sansuis but this one needs a re-cap too.

In the end, I don't know what specifically fixed it. I have a Blue ESR meter so I may test the caps to see if they were terrible.

 

[gadget73]

I'd bet more on a bad solder joint or a flaky transistor than a cap. Caps can cause problems but my experience with them so far is that its not usually intermittent like that unless the leg is ready to rip out. Usually that happens when you pull it off the board. A busted connection inside the can will act just like any other bad connection but its harder to spot unless you happen to bump the cap randomly and find it.

When I've had funny stuff like this before usually I start tapping around on the board with some sort of insulated thing. usually somewhere it will start flaking out, from that point I just narrow down on the area by reducing how hard I tap. Most of the time within a few minutes I can find busted solder or cracked foils that way. Usually won't find the exact spot with the tapping but I can generally narrow it down enough that a visual inspection will find it.