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2275: Loud crackly burst sound on left channel after approx 10 seconds after turning on!

absolve2525

absolve2525

Super Member
This unit has been recapped, and I just changed the relay delay resistor R813 to 390K as suggested on here. It didn't help. The loud crackly sound seems to go away after a moment, but I think it comes back spontaneously if I recall correctly. I shelved this unit for a while. DC offset jumps up while this happens.
It had this issue for as long as I have owned it. DC offset has been adjusted super low, aside from the burst on power up. Power supply board is spot on at 35V. Perhaps a bad trimmer? Solder joint? Bad main transistors? Power supply board issue? New relay has been installed as well as new small transistors on the amp boards. Outputs are original. I also changed out the resistors next to the BA312 ICs for 390K, which helped some people. That didn't help. I am going to double check if it's Amp or preamp, I forgot this model may have spring loaded preamp out/main in. Update: it will happen on one or both channels. It's sporadic apparently, not just at power up but most likely then. I'm pretty sure it's the amp section, after plugging in two separate rca cables into preout/main in. Geeze, the spring loading was confusing things.
 
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I replaced the diff pairs on both amps a while back, still no luck. Yeah, it happens with main ins shorted. I'm running out of things to replace argh. Thanks for the suggestions.
 
absolve2525 said:
I replaced the diff pairs on both amps a while back, still no luck. Yeah, it happens with main ins shorted. I'm running out of things to replace argh. Thanks for the suggestions.
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if it happens with main in shorted you narrowed it to the amp itself. I know it is unusual but I had 2325 and 2275 with flaky drivers. on 2275 I've seen them replaced either with MJE15030/31 or KSC2073/KSA940
 
Thanks, I may have some of those on hand! It's prob that last thing I have looked into, since I figured they were pretty robust. Maybe a flaky batch, who knows. It can happen.
 
using heat, and freeze spray, as well as a Variac to raise and lower voltage can most times help in locating an intermittently noisy device
 
Ceeck/clean the switch on the back that couples/de-couples the pre-amp from the main amp. It is a frequent source of problems on Marantz units. If that is not the issue
I would focus on the PE01 tone/pre-amp board. The BA312 IC and the four transistors on that board are a frequent source of crackling noises etc. on the 2275.
 
ocdecio said:
if it happens with main in shorted you narrowed it to the amp itself. I know it is unusual but I had 2325 and 2275 with flaky drivers. on 2275 I've seen them replaced either with MJE15030/31 or KSC2073/KSA940
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I've made my way down to the driver transistors. Pulled them and they both test good. Does that mean they may still be flaky? I ruled out the output transistors. I swapped in some new ones, and the intermittent noise persists. I found that I don't have any of the old blob diodes in this unit. Should I still be checking for diode issues? Can anyone recommend a source for new driver transistors? I've narrowed down the noise to the amp section. There's no preamp out switch on the back. Thanks!
 
You are right about the pre-amp out switch. I forgot that that function is built in to the main in jack if I remember correctly. I would suggest that you use RCA audio cables to connect the left main in and Pre-out jacks as well as a second cable to connect the right Main in and Pre-out jacls to eliminate the internal switch as an issue. I have had that experience in the past. Sometimes just inserting and then removing the RCA jacks will clear a noise issue with the internal switch function.



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Placing patch cord into the preamp to main circuit will test the connections in question.
 
I'm still trying to sort this out, grrr. I pulled the amp boards, and tested all the transistors and diodes. They all measure good. I don't see any bad solder joints. One channel goes static-y shortly after turning on, short burst that doesn't trigger protection. The other channel does so sporadically. This all happens randomly. I have separated amp and preamp sections, so I don't see how this could be preamp related. Could a bad trimmer cause this? Power supply transistor? It's not both channels at the same time and can happen at any time.
 
I owned a Marantz 2325 that had random crackling in one channel that was caused by a bad trimmer. The 2325 used wirewound trimmers which I had never seen before. Have you tried cleaning the trimmers in your unit?
 
Did you use the patch cables as suggested in post #11? If so, I'd try replacing the transistors right after the diff pair next, H703 and H704 as they're small and more easily replaced.

2SA721: KSA992
2SC1327: KSC1845
 
rBuckner said:
Did you use the patch cables as suggested in post #11? If so, I'd try replacing the transistors right after the diff pair next, H703 and H704 as they're small and more easily replaced.

2SA721: KSA992
2SC1327: KSC1845
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Apparently I already did update/replace those particular transistors. I have not done 705—708. Thanks for the suggestion though
 
I finally realized I can swap right and left amp boards easily. I did that, and the distortion stays on the same left channel regardless! I have separated amp and preamp with RCAs. Im going direct into the amp section from the source bypassing preamp. I get this distortion primarily on startup up and then sporadically. What's left here? Bad main caps? Power supply issue? It has a new relay and board is recapped. Thanks
 
absolve2525 said:
I finally realized I can swap right and left amp boards easily. I did that, and the distortion stays on the same left channel regardless!
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Wait a second.
  • Did you physically swap the R and L channel boards, in the chassis, and was the distortion still in the L channel?
  • Unless I misunderstood what you did, this indicates that the problem is not with the P700 board, but something else.
  • To determine whether it is caused by the Preamp or Main amp, you first need to cross-connect the Pre-out and Main In with a short stereo RCA cable (Pre-out L to Main In R, Pre-out R to Main In L).
  • If the problem remains on the L, then it is the Main Amp. If the problem moves to the R, then the problem is in the Preamp.
 
I have
dankik said:
Wait a second.
  • Did you physically swap the R and L channel boards, in the chassis, and was the distortion still in the L channel?
  • Unless I misunderstood what you did, this indicates that the problem is not with the P700 board, but something else.
  • To determine whether it is caused by the Preamp or Main amp, you first need to cross-connect the Pre-out and Main In with a short stereo RCA cable (Pre-out L to Main In R, Pre-out R to Main In L).
  • If the problem remains on the L, then it is the Main Amp. If the problem moves to the R, then the problem is in the Preamp.
Click to expand...
I have jumpered left preamp out to right main-in, and vice versa. It problem remains mainly on the one side, with bursts of loud static and cone movement shortly after turning on. Then, I physically swapped right and left amp boards. It does the same thing. The main caps were already replaced with more modern 22000uf caps, but I don't know the history on them. I'm not the original owner. So yes, it doesn't appear to be the preamp and now doesn't appear to be amp boards themselves since the same result after swapping them right and left. Thanks
 
It may be bad contacts on the speaker protect relay (L801) on the P800 board. It looks like you put in a new one, so check the board for cold solder joints.
Or, it could be dirty Main and Remote speaker switches. Make sure you clean them with Deoxit or contact cleaner if you haven't already done so.

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