Marantz 4140 Bass thump issue

[nolannnniah]

Well, I got a Marantz 4140, for about 350 with the SQA-2B decoder.

I have recapped all boards with the exception of the main power caps & phono board (don’t use it currently, but do have replacements on hand). I did the power amp boards, power protection board, matrix board, pre-amp board and the decoder. I aligned the power amp boards, and power protection board.

I was having periodical bass thumping in the speakers prior to the re-cap and still have it now. It does it within the first 2-5 minutes after power up, and sporadically during operation. The unit is grounded to wall and I can't seem to locate the issue-all voltages seem to be good. Only thing I can think of is the main power caps...Ideas? The unit also likes to do the bass pop/thump thing when the tuner is turned on. It is also grounded and only connected to the 4140 by RCA cables. It happens in both modes (x2 or x4 mode selection on rear of unit). All pots and push-button switches have been cleaned and worked well. Could the issue be at the phono board? Would that make an impact on the rest of the system, if a cap was faulty?

Also, none of the film or ceramic caps were replaced. I was thinking about replacing the tone board with NOS I have run across, but would like to solve this issue first. I am hoping that the tone board replacement will fix the slightly flat tone I have now.

The VU meters don't seem to read correctly: 2 seem to "struggle". The meters work, but do not seem to want to go as far as their counterpart channels, even in mono mode (x2 & x4). Almost seems like they are slow to respond and don't go as far to the right as they should vs. other channel.

Any ideas and inputs are welcome. Unit does work and everything functions as it should (with the exception of issues listed above).

Also, the selector switch is a bit tough to turn, but does not appear to be bent...is this normal? Pic below is for reference and is not my own.

Thanks-Nolan

 

[leevitalone1]

Try Deoxit on the switch. as for the rest, you may want to ask this at the AVS forum, where I have seen people re do them from the chassis up.

 

[nolannnniah]

Thx for the info, will try there.

 

[Quadwreck]

I had that problem on a 4230, cleaning the bass pot cleared it up, I've also had that problem with another model (stored away, can't see it), cleaning didn't fix it.

 

[nolannnniah]

I was leaning towards the tone board. Going to clean and touch up joints on board and see if that fixes it...If not might drop in the NOS I found. Thx-

 

[Doug G.]

The main filter caps should be replaced.

Doug

 

[nolannnniah]

I was hoping someone wouldn't say that. I was leaning towards the tone board (that way I can "justify" getting a NOS one for the slightly flat sound), then the main caps. I figured as much due to what I have done and what it is doing...they are like $30+ each... Would it be an issue to go up to 22000uF, from 20000uF?
Thanks-Nolan

 

[Doug G.]

It's just that those caps undergo a fairly rough life in electronical terms with high currents passing through them and such so I have always replaced them or have had to replace them in vintage amplifiers. 20K to 22K will be fine.

I have had similar symptoms from amps such as you are having and the power output caps were it.

Doug

 

[nolannnniah]

Ok, cool, thanks for the input & help.

Nolan

 

[Doug G.]

A couple of other thoughts re your original questions. If the amplifier is already on and you turn the tuner on, any DC component resulting from the output of the tuner stabilizing can cause a thump and that's normal. The usual order in turning things on is to turn all the sources (tuner, tape deck (s), etc.) on first and then the power amplifier. That way, the source equipment is stabilized when you turn on the amp.

If there were a problem in the phono section, it should not cause any thump as long as the source switch is not turned to "Phono" as that section really isn't in the circuit at that time.

The VU meters can be addressed after the thump is taken care of.

That's such a beautiful amplifier, it certainly deserves to be operating 100%

Doug

 

[nolannnniah]

OK, will do for power up. I am going to grab some new caps at the end of the month. I agree, love the amp! Wish I would have gotten one sooner. Have been a fan of vin. pioneer, but wanted to give a good quad a chance-So i went with this one and I am very impressed. This is more of a hobby of mine vs. an income. Now I just have get some good test equipment vs. trying to use the stuff i have at work durning my lunch!
Will keep the fourm updated once I get them in-Thanks again

Nolan

 

[nolannnniah]

Ok, replaced the main caps. Powered up amp and still had some vu meter flutter-only for the first few minutes. I went back and realigned the power amps and the main voltage via the service manual. Did that after about an hour of it being powered on and shut it off. Have not hooked up speakers yet (to see if the thump is still present). Should I do a "burn-in" with 8Ohm 100W dummy loads? If so, how long should I do it for?
Thanks-

 

[Doug G.]

The new caps shouldn't need burn-in. They should work right off the bat. I would just hook speakers up (do you have any expendible ones?) and see if the thump is gone.

The VU meter flutter is still a bit of a worry. It could be benign and just in the meter drive circuits or it could mean instability in the audio chain.

Oh well, as we always say in the electronical repair field, "At least we know THOSE caps are good!"

Doug

 

[nolannnniah]

Ok, plugged in a pair of JBL HLS610s (@ 8Ohms-some bookshelves). Still got the meter flutter, but no thump which is good...I tried to recreate it again, after I hooked it all up. It only did it (meter flutter only), after it was off all day. After it has been running for a few, it doesn't do it when I turn it off and on. Powering on & off (trying to create the pop/thump & and meter flutter): I tried leaving the volume up, selecting speaker input (on & off a few times) while on, changing source of input (volume 1/4 of the way)...no popping or thumping. Just the very, very, very slight kick when relay pops on-had volume @ 1/2 way.
Keep in mind this is the second time I have had power to these 2 main caps-should that matter?...While amp is on I get great sound and my tones opened up a lot. They are very warm and rich, with good definition-compared to before the replacement. Still have the "struggling" vu meter though.

Nolan

 

[Doug G.]

It sounds good so far as far as the thumping and it's normal for transcients to cause a bit of extraneous noise from relays switching or switches being switched. It shouldn't be very loud, however.

Just keep using it and see if it's really fixed. Those caps should be OK from the start and no matter how many times you put power to them. The modern day idea that caps need some kind of lengthy break-in or burn-in is nonsense. No manufacturer would make them like that. They are made to be put into a circuit and work right away.

There must be a problem in power for those two meters since it's common to both of them for that channel. You did say it was both of them (front and back) on one of the sides, right? Usually the way they work is a sample of the signal is taken from the preamp or amp and changed to DC to operate the meter. Any extra DC getting in there intermittantly will make the meter(s) jump or if the DC voltage is low, the meter(s) will be sluggish. Of course, it could be just an intermittant connection too.

At least, if the meters are acting up but there isn't any thumping the two aren't related and that's good, in a way.

Doug

 

[nolannnniah]

Ok, I'll keep an eye on things and see what happens. Meters: Yes, it is the right front and left rear meters (when in x4 mode)-that are the "sluggish" ones. Leading me to believe it is signal path from one of the 2 amps. But the meter flutter from initial power up (after amp has been off a while), is reflected in all the meters-when in appropriate mode. Only left & right do it when in x2 and all 4 when in x4 mode. Only thing I can think of off the top of my head is the AC rectif. assy.??, but those caps are film (x2 0.022uF +/- 20% @ 400v). From my understanding they either work or don't, and have a very, very low failure rate. Also, 4 diodes (U11C x2 & U12C x2) that I can't find a cross ref. for.

 

[nolannnniah]

Any ideas out there? Have it open on the bench...
Thanks, Nolan

 

[Doug G.]

As far as the fluttering, if it affects all four meters, it has to be something in common with them all. The way to check the "sluggish" ones is to make sure you have equal signal to all channels, such as a mono signal and see what they do. In other modes, you can't tell if the meters are responding wrong or if the actual signals to them are different since, in a quad unit, the decoders will send vaying signals to the different meters depending on what is sent to the four speakers.

I have a Heathkit AA-2010 quad amplifier and sometimes it seems some of the meters are acting differently than the others but it's the signals being sent to them that are different. If I set the unit to mono, they all act the same.

Doug

 

[nolannnniah]

Sorry for the long time in-between posts...for the meter issue-I still have the same problem in mono. I did notice, after I cleaned and re-worked the tone control & pots (PJ-01 if you have the SM) and the tone amp assy. (PD-01), that when the bass pot is moved it make them flutter some-only when turning from no bass to adding some in (from far CCW position to CW direction). Then I switched the selector pot through the different selections (S001 pot), and it pegged the meters and tripped the power protection relay. After a few seconds it came back on. I cleaned and re-worked those 2 boards because it did start thumping through the speakers. As I stated before, it does calm down/go away after it has been on a few. Although, a couple of days ago when I turned it up to work the unit a little, after a few seconds of pushing it, it tripped too. It did come back on a play at the same volume, but meters fluttering here and there with no thump. So I turned it back down & let it play for a bit (meters stopped fluttering). I put it back on the bench re-did those boards and checked voltages and offsets on the power amp assy.'s. all read good. So this leads me to my pre-amp assy. or before it. It is the only thing I can think of that would cause issues across the whole spectrum ATM. I have changed the caps on it already, but have not completely cleaned and re-worked it yet (pre-amp). When I pulled the jumpers (main-in; pre-out), I did not see the issues. I might not have left it on long enough, but I can only stare at the meters for so long. I don’t believe it is the pre-amp, but input before it...It is just such a pain to get at with everything still wired in. When looking at the schematic, everything is divided into 4 channels and it does not seem to have a single point of failure/component that would cause all 4 channels to be this way on the pre-amp board. I am going to try cleaning the x2 & x4 selector pot in the back (S004) and check my main power board assy. for correct voltages on it...I'll post back with my findings. If anyone has any other suggestions please feel free to share.

Nolan

 

[nolannnniah]

My 4140 & a 2238 I'm almost done with.