So I am working on a marantz 2238B that had intermittent distortion. Someone else had replaced a couple caps and the relay thinking it would fix the problem.
Long story short it ended up being a scratchy mono switch that needed to be bypassed as DeOxit didn't fix the issue and disassembling the entire switch board was not an option. I also replaced the previously replaced caps and replaced all electrolytics in the preamp and source switch board. Last thing done was replace all lights with equivalent.
Issue now is I have a constant buzz noticeable with the headphones. It is loud enough to detract from headphone listening.
My first thought was bad caps or maybe a missed ground. I double checked all grounds and everything looked appropriate. I also internally separated the preamp from the amp to narrow down the hum. After I still had hum through headphones so it is most likely the amp portion.
This led me to replacing all caps in the power supply and amp board. Still hum!!!
At this point I am running out of ideas. I checked solder joints and reflowed where I thought necessary.
Anyone have any bright ideas?
One thing I didn't do is use the headphones prior to my initial repair (mono switch bypass) so I don't know if it was present before any work I did. Also don't know if I mentioned but hum is constant regardless of volume and with shorted rca inputs.
Thanks for the help
Long story short it ended up being a scratchy mono switch that needed to be bypassed as DeOxit didn't fix the issue and disassembling the entire switch board was not an option. I also replaced the previously replaced caps and replaced all electrolytics in the preamp and source switch board. Last thing done was replace all lights with equivalent.
Issue now is I have a constant buzz noticeable with the headphones. It is loud enough to detract from headphone listening.
My first thought was bad caps or maybe a missed ground. I double checked all grounds and everything looked appropriate. I also internally separated the preamp from the amp to narrow down the hum. After I still had hum through headphones so it is most likely the amp portion.
This led me to replacing all caps in the power supply and amp board. Still hum!!!
At this point I am running out of ideas. I checked solder joints and reflowed where I thought necessary.
Anyone have any bright ideas?
One thing I didn't do is use the headphones prior to my initial repair (mono switch bypass) so I don't know if it was present before any work I did. Also don't know if I mentioned but hum is constant regardless of volume and with shorted rca inputs.
Thanks for the help
So I must have spent a couple weeks off and on trying to tackle this hum. I finally decide to make a post then I actually start to get somewhere.
First thing- if I short the headphone channel the hum goes away. Not sure how much that helps.
Second thing- if I touch a wire to the ground of the headphone jack and then touch the other end to the chasis or any ground spot (ie: the power cap ground bar) I get silence.
Listened to it for a while without any issues. So I have narrowed it down to a ground loop or something of the sorts. I decided to just solder the wire hoping to be done with it but it appears making a soldered connection is different then touching the wires as the hum is reduced but still there.
At this point I know I have grounding problems. Going to go through and check all of them. It appears the amp has an unusual grounding scheme as part of it appears to be star but there are multiple points that are grounded directly to the chassis.
Again any help is appreciated and I'll post any updated ad I move forward.
First thing- if I short the headphone channel the hum goes away. Not sure how much that helps.
Second thing- if I touch a wire to the ground of the headphone jack and then touch the other end to the chasis or any ground spot (ie: the power cap ground bar) I get silence.
Listened to it for a while without any issues. So I have narrowed it down to a ground loop or something of the sorts. I decided to just solder the wire hoping to be done with it but it appears making a soldered connection is different then touching the wires as the hum is reduced but still there.
At this point I know I have grounding problems. Going to go through and check all of them. It appears the amp has an unusual grounding scheme as part of it appears to be star but there are multiple points that are grounded directly to the chassis.
Again any help is appreciated and I'll post any updated ad I move forward.
Interesting. The Ground only becomes Chassis at the power amp section. It is a virtual ground up to that point, so as there is a 47R holding the ground point together and I have only read about it at Marantz Seminars and not had this problem in any I have repaired in or out of warranty, maybe if you cant find it, hang a 47R 1/4W between the chassis and earth at the pre amp end instead of your hand.
Thanks for the information. This weekend I am going to try and tackle this ground issue.
Looking a the actual grounding scheme in the amp I noticed several points where the unit is grounded to chassis. The amp board is grounded to the chassis at three points I can tell so far. One large wire underneath that comes off the ground by the output transistors, another off a post the is connected a secondary winding center tap, and last a ground post near the front right corner.
Preamp is only grounded to the chassis at the preamp out RCA jack in the back which is also strapped to the main amp out RCA jack. This chassis ground point is also strapped to the neutral of the accessory jacks. The last chassis ground I can appreciate is attached to the several RCA inputs on the back of the unit.
Tough to say at this point how all these are interconnected as there are several ground wires interconnecting everything. This is especially true on the amp board where underneath there are several ground wires coming from the same ground potential and going to the the bus bar.
I also want to clarify how I was able to get the hum to disappear. Initially, I touched a wire to the metal on the 1/4 headphone plug and touched the chassis. This made the hum disappear. I then soldered a wire to the the ground post on the back of the jack that is attached to the ground shield of the signal wire. I touched the other end to the chassis with the same results. I then secured the wire under a screw close by and it only slightly reduced the hum (weird??).
Next I touched the ground between the power caps with the same wire and the hum disappeared. So I decided to solder it in place and had the same results with the screw, the hum was back and only slightly decreased. Next I just wedged the wire against the ground bar so I could let go of the wire... hum completely gone!!! I listened to the unit for several minutes and power cycled the unit without issue.
Does this have to do with messing up the 47ohm resistance discussed above?? Or does this mean I need to wrap the wire around a ground post and not actually solder??
Hopefully I will have some more results soon
Looking a the actual grounding scheme in the amp I noticed several points where the unit is grounded to chassis. The amp board is grounded to the chassis at three points I can tell so far. One large wire underneath that comes off the ground by the output transistors, another off a post the is connected a secondary winding center tap, and last a ground post near the front right corner.
Preamp is only grounded to the chassis at the preamp out RCA jack in the back which is also strapped to the main amp out RCA jack. This chassis ground point is also strapped to the neutral of the accessory jacks. The last chassis ground I can appreciate is attached to the several RCA inputs on the back of the unit.
Tough to say at this point how all these are interconnected as there are several ground wires interconnecting everything. This is especially true on the amp board where underneath there are several ground wires coming from the same ground potential and going to the the bus bar.
I also want to clarify how I was able to get the hum to disappear. Initially, I touched a wire to the metal on the 1/4 headphone plug and touched the chassis. This made the hum disappear. I then soldered a wire to the the ground post on the back of the jack that is attached to the ground shield of the signal wire. I touched the other end to the chassis with the same results. I then secured the wire under a screw close by and it only slightly reduced the hum (weird??).
Next I touched the ground between the power caps with the same wire and the hum disappeared. So I decided to solder it in place and had the same results with the screw, the hum was back and only slightly decreased. Next I just wedged the wire against the ground bar so I could let go of the wire... hum completely gone!!! I listened to the unit for several minutes and power cycled the unit without issue.
Does this have to do with messing up the 47ohm resistance discussed above?? Or does this mean I need to wrap the wire around a ground post and not actually solder??
Hopefully I will have some more results soon
After unsquashing, I can see that headphone ground should be coming from the power amp, J737-ish, serving as the reference for a 330/150R resistor divider before going on to the headphone jack via J714 - basically an OK scheme. I can only guess that you may have an iffy connection somewhere along the line (what does the ohmmeter have to say?). Sometimes it works and forms a ground loop with your extra ground connection, reintroducing the buzz.
There should only ever be exactly one single (audio frequency) connection from audio ground to chassis, and that's the one in the power supply (drawn next to the 10000µ/50 caps).
There should only ever be exactly one single (audio frequency) connection from audio ground to chassis, and that's the one in the power supply (drawn next to the 10000µ/50 caps).
My next step is to check along the grounding path for the headphone jack. I too think something has probably come loose or something.
Sorry about the squished schematic. In reference to the single ground to chassis, the amp had a preamp out and main amp in (RCA) typical for receivers but is actually internally connected. This signal is also strapped to the chassis at that point. I lifted this to see if it help but it did not.
Sorry about the squished schematic. In reference to the single ground to chassis, the amp had a preamp out and main amp in (RCA) typical for receivers but is actually internally connected. This signal is also strapped to the chassis at that point. I lifted this to see if it help but it did not.
Spent some time with the receiver this morning. The grounding scheme is very complicated.
I have created three scenarios:
- If I touch the wire (one connected to the jack ground) to any ground spot I get dead silence.
- If I touch the wire to a chassis ground or any part of the chassis I get reduction in hum but it is still fairly noticeable.
- If I touch the wire to the ground point that is directly inline with the ground point associated with the original ground wire off the jack, I get no change (makes sense to me)
The kicker is if I solder the wire to a ground point I get hum.
Solution: Most if not all the ground wires are wrapped around the ground point for the boards and not actually soldered. So I took a solid core wire, soldered one end to the ground of the headphone jack and wrapped the other end around a ground point on the preamp board.
Result... No hum!!!
Everything is working great. Headphones have dead silence when no audio is played. Obviously this is a workaround for some ground issue. Unfortunately I cannot find it and am a bit tired of searching.
Thanks for those that offered insight into the problem. I think talking (or typing) it out got the brain cells firing.
I have created three scenarios:
- If I touch the wire (one connected to the jack ground) to any ground spot I get dead silence.
- If I touch the wire to a chassis ground or any part of the chassis I get reduction in hum but it is still fairly noticeable.
- If I touch the wire to the ground point that is directly inline with the ground point associated with the original ground wire off the jack, I get no change (makes sense to me)
The kicker is if I solder the wire to a ground point I get hum.
Solution: Most if not all the ground wires are wrapped around the ground point for the boards and not actually soldered. So I took a solid core wire, soldered one end to the ground of the headphone jack and wrapped the other end around a ground point on the preamp board.
Result... No hum!!!
Everything is working great. Headphones have dead silence when no audio is played. Obviously this is a workaround for some ground issue. Unfortunately I cannot find it and am a bit tired of searching.
Thanks for those that offered insight into the problem. I think talking (or typing) it out got the brain cells firing.
A quick update:
After I reattached the preamp and amp internally I had return of the hum. It would go away if I had an external preamp connected providing the ground. I ended up removing the previous extra ground coming off the headphone jack. Hum actually improved slightly with removal.
I went ahead and Soldered another wire to the headphone ground and touched around the receiver and found a ground post on the input select/phono board that removed the hum.
I used solid core wire an wrapped around the post (no soldering) and now the unit is dead silent. Everything is back together and sounding great.
Wish I could have found the actual culprit but the grounding scheme is complicated on the receiver (schematic doesn't accurately reflect this) and my head hurts from banging it against the wall.
After I reattached the preamp and amp internally I had return of the hum. It would go away if I had an external preamp connected providing the ground. I ended up removing the previous extra ground coming off the headphone jack. Hum actually improved slightly with removal.
I went ahead and Soldered another wire to the headphone ground and touched around the receiver and found a ground post on the input select/phono board that removed the hum.
I used solid core wire an wrapped around the post (no soldering) and now the unit is dead silent. Everything is back together and sounding great.
Wish I could have found the actual culprit but the grounding scheme is complicated on the receiver (schematic doesn't accurately reflect this) and my head hurts from banging it against the wall.
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