Marantz 2252 POP when turned off

C

CavScout

Super Member
I just did a full recap of a Marantz 2252.
The reason for the recap is because I bought the unit many years ago (untested) and it had a LOT of problems.
The recap went well and a bunch of other transistors along the way.
Everything seems to be working well...except 2 things.
When I turn it on it comes out of protection VERY fast...almost instantly.
And when turned off there is a loud speaker POP even with the volume down.
Note : Power supply voltage was adjusted per the manual to 35 vdc (after a 45 minute adjustment period).
I also did the power amplifier adjustments to 8 mvdc.
The other trimmer adjustment was impossible to do (R711 & R712) because the MM was not holding still. It was bouncing too much.
I adjusted that as best as I could.

Does anyone have any suggestions on what could be causing that POP and how to fix it ?

Thank you

Here is a video that I made

 
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Maybe the relay has had one or both sets of contacts welded together, it does happen. Other than that, check out the relay driver / protection circuit, Q738-740 and associated components. Someone may have soldered wires across the relay contact points too! :yikes::yikes::yikes:
 
Listening to your audio, the "scratchy" noise sounds like it might be transistor thermal noise.
  • Can you hear the relay click on with power and click off with power off?
  • Try to isolate it between the Preamp and the Main Amp by disconnecting the Pre Out-> Main In jumpers (you may need to put an RCA cable into the Main In to disconnect it).
  • The loud thumping noise on turn off could be capacitors discharging, possibly because of issues setting the DC offset you mentioned above (R711, R712). Try to clean (or replace) the VRs and see if this helps.
  • The relay power switch goes through the main power switch can you verify that when you turn it off it cuts off power to the relay.
  • Do you hear the same noises if you turn off the speakers and listen using headphones?
 
dankik said:
Listening to your audio, the "scratchy" noise sounds like it might be transistor thermal noise.
  • Can you hear the relay click on with power and click off with power off? YES
  • Try to isolate it between the Preamp and the Main Amp by disconnecting the Pre Out-> Main In jumpers (you may need to put an RCA cable into the Main In to disconnect it). WILL DO THIS
  • The loud thumping noise on turn off could be capacitors discharging, possibly because of issues setting the DC offset you mentioned above (R711, R712). Try to clean (or replace) the VRs and see if this helps. THE VR POTS ARE NEW
  • The relay power switch goes through the main power switch can you verify that when you turn it off it cuts off power to the relay. YES IT DOES
  • Do you hear the same noises if you turn off the speakers and listen using headphones? SAME WITH THE HEADPHONES
Click to expand...
 
The delay circuit in the protection system is not working, either due to a shorted transistor or diode or an incorrect or incorrectly installed capacitor. You'd have to look at the circuit to see, usually there is an input for power on, output voltage or overcurrent, and DC stability of the power supply.

Many higher power units disconnect the relay when the power is shut off to prevent that thump, if the circuit isn't working properly (instant on rather than a few seconds delay) it may not be disconnecting properly either.

If you have a schematic the voltages are listed, should be able to isolate the bad part(s) by comparing what you have to what is supposed to be there.
 
Ok so I hooked up a Marantz 1070 to the MAIN IN on the 2252 and there are no problems. No funny sounds, no pop etc.
When I reversed things and hooked up the 2252 to the 1070 MAIN IN..
all of the problems were present.

So does this mean the problem lies in the 2252 PE01 Tone board ?
 
One main amp board check Caps C721 and C722 for correct orientation and lack of solder bridges. Check transistors Q739 and Q740 for shorts -- I believe C722 is supposed to provide the relay delay and Q738 the shutoff release, but I'm new at this. A shorted transistor at 739 or 740 (or a solder bridge) would energize the relay when switched on instead of a few seconds delay, and hold it closed at power off instead of opening to allow the caps to discharge with the speakers disconnected.
 
CavScout said:
Ok so I hooked up a Marantz 1070 to the MAIN IN on the 2252 and there are no problems.
Click to expand...
Good!
HPMguy said:
One main amp board check Caps C721 and C722 for correct orientation and lack of solder bridges.
Click to expand...
The Main Amp appears to work OK when connected to another preamp, so probably not.
CavScout said:
So does this mean the problem lies in the 2252 PE01 Tone board ?
Click to expand...
Could be, but also check the things below.
It sounds like it is not the P700 board on the 2252, but could be the PE01-Tone Amp or P400-Phono & Selector.
I think on your video you stated that the sound was still there with the volume control turned all the way down, correct?
The volume pots could be oxidized. If you haven't already done so, clean them with Deoxit.
If the noise is occuring on both channels, you need to look for a problem common to L & R on the Tone Board. Have you cleaned the tone controls with Deoxit?
Lastly, check for dirty (oxidized) RCA jack contacts on the PreOut and Main In and clean with Deoxit, if not already done.
 
I admit, I didn't run the video. There WAS a delay between power on and the first pop so it wasn't immediate as earlier described.

Now that sound like wind blowing on a microphone sounds a lot like a backwards electrolytic cap. There would have to be one in both channels though if heard on both speakers. That would also act nasty on power up and power down and make for popping.

Please post some clear pictures of the tone board. Turn on the flash so there are no deep shadows.
 
Here are some pictures of the tone board.
 

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dankik said:
Good!

The Main Amp appears to work OK when connected to another preamp, so probably not.

Could be, but also check the things below.
It sounds like it is not the P700 board on the 2252, but could be the PE01-Tone Amp or P400-Phono & Selector.
I think on your video you stated that the sound was still there with the volume control turned all the way down, correct?
The volume pots could be oxidized. If you haven't already done so, clean them with Deoxit.
If the noise is occuring on both channels, you need to look for a problem common to L & R on the Tone Board. Have you cleaned the tone controls with Deoxit?
Lastly, check for dirty (oxidized) RCA jack contacts on the PreOut and Main In and clean with Deoxit, if not already done.
Click to expand...
I have already cleaned the volume and tone pots with deoxit and just did it again.
I also cleaned the main in/pre out just now.
Problem is still there.
 
DC offset in the pre-amp? Might check that, although it shouldn't make it through C23/24. Did you use film caps there?
 
Yes film caps on those.

The manual does not mention DC offset procedure (unless it is called something else in the manual)
 
Would be a component issue (on both channels....) as it's not adjustable except by replacing parts, just something to look at.

You are getting a voltage spike at power on and power off that is getting past the coupling caps, so it's AC of some sort. Appears at relay operation, which is why I suspect the protection circuit, but I'm not familiar with Marantz equipment.

Would not hurt to check DC offset at the outputs either, although a problem there would be there no matter what the input the power amp is connected to.

The +35 is common to power and pre-amp, so that's not likely to be the issue.
 
Here is another video ( Reminder the sound is coming out of both speakers and the volume is all the way down )
 
I keep looking for something common to both channels on the pre-amp board to see what could be making your noise.

Is Ce25 properly oriented and well soldered? it's a noise filter for the power supply (+35 to ground) and should eliminate any
AC spike on the +35 line. I've failed to get good solder joints more times that I'd like to count, and it's always possible (if somewhat unlikely) that you got a bad one. Cracked trace or pad broken off will prevent it from working too.
 
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