Nasty "POP" - RC-M60JW

[Marshall]

When switching from "TAPE" of "LINE IN" to "RADIO"

Does NOT matter if the Volume control is up or totally defeated (that's the oddest part of this issue)

Does NOT "pop" going from "RADIO" to "TAPE" or from "RADIO" to "LINE IN"

All functions work well on this machine (except for the woofer issue currently being pursued) and all controls have been cleaned and work well except for this nasty little "pop".

If it were a power switch on an old tube amp I'd strap it with a resister and a cap in series; it's that same sort of "pop"

Any thoughts? Solutions? Was this normal behavior? I don't have enough experience with JVCs or boxes of any kind to know.

I'd like to get rid of it when I go in to do the cap job eventually and it would be nice to know if there's something to look out for or possibly something I could do in the meantime. Actually, I'd LIKE to be rid of it right now; it can't be doing anything any good. And again, it is not volume control dependent, it does it just as long as the machine is "ON"

I know the tweeters would HAVE to appreciate it! I am starting to wonder if this has any connection with the fact that everyone that's offered help and insight regarding my dead woofer search has also commented that their M60 too had one bad woofer. Seems to be very common with this model: the M60 ONE dead woofer syndrome?

But one would think a transient "pop" like this would be killing tweeters, not woofers.

If someone knows of this and it's a pattern failure cap, I'd need a board number as my service manual has yet to be ordered.

Anyway, any help with this would be well received.

Thank you,
Marshall

 

[Marshall]

Bump and hoping someone has had to deal with this one before.

I am not going to be able to do a total re-cap on this box right now and for the next few months but I could still possibly manage a cap or two if that's what it is (in the next few days).

Right now I'm just powering off when making the switch; this nasty little pop can't be doing the speakers any good.

And I'm still curious though; was/is this "normal" behavior?

Whatever, it's got to go!

Thanks to all,
Marshall

 

[BoomboxLover48]

Change from mains to battery for power supply and see if it does the same.
If it goes away we can conclude it has to do with the power supply.

 

[Beosystem10]

Mains filter cap. That's the class X2 or Y2 (our regs may be different from yours so you need to check this for yourself to be certain that you're complying) one connected across the mains before the transformer, between phase ("live") and neutral in the case of this double insulated, single phase device which isn't earthed at the socket.

Presumably you'll have loads of these seeing as you're into your valved equipment, the same one that you'd use between chassis and phase in a universal or as above in an AC set.

 

[BoomboxLover48]

Mains filter cap. That's the class X2 or Y2 (our regs may be different from yours so you need to check this for yourself to be certain that you're complying) one connected across the mains before the transformer, between phase ("live") and neutral in the case of this double insulated, single phase device which isn't earthed at the socket.

Presumably you'll have loads of these seeing as you're into your valved equipment, the same one that you'd use between chassis and phase in a universal or as above in an AC set.

That is it! It is the filter cap! John is right! (Always)

 

[Marshall]

Mains filter cap. That's the class X2 or Y2 (our regs may be different from yours so you need to check this for yourself to be certain that you're complying) one connected across the mains before the transformer, between phase ("live") and neutral in the case of this double insulated, single phase device which isn't earthed at the socket.

Presumably you'll have loads of these seeing as you're into your valved equipment, the same one that you'd use between chassis and phase in a universal or as above in an AC set.

Thank you!
And I actually have two bags of them.

I'll check it out. (still don't have a service manual so I hope it's an easy one to find on the board if that's where they put it. The transformer and mains cord attach sits alone down in a corner near the battery compartment as you guys already know)

But curious; why only switching to RADIO and nothing else if it's a steady state cap failure? NOT arguing with your suggestion, I'll change it out no matter. Is the tuner section powered off electrically when LINE IN or TAPE is in use? (again, the reason why I and everyone need a service manual!)

I will also mention that the channel that had the dead speaker also has a VERY FAINT (like you can only hear it with your ear pressed to the box hum) so I was already fretting over a possible PS problem as well. Just didn't think they'd be related and once passing a signal the box sounds great now thanks to JustCruisin.

I checked DC off set on the outputs and that's fine.

Thank you very much for the direction,
Marshall

 

[Beosystem10]

Royce, I wish!



(I was right once. It was 1984 and Secreto won the Derby at 14 to 1. I had £5 each way on that amazing horse..)

I've never gambled since, least of all with things that go bang if you get it wrong..


OK, just one more thing then, Marshall: What happens if you run the tape motor and then, with the motor running switch the input selector to radio?

 

[Marshall]

Royce, I wish!



(I was right once. It was 1984 and Secreto won the Derby at 14 to 1. I had £5 each way on that amazing horse..)

I've never gambled since, least of all with things that go bang if you get it wrong..


OK, just one more thing then, Marshall: What happens if you run the tape motor and then, with the motor running switch the input selector to radio?

Good Morning!
Just verified; same deal
Played a tape and then switched "MODE" selector to "RADIO".........POP
Switch from "RADIO" back to "TAPE" OR "LINE IN"..........NO POP

The POP only occurs when switching TO RADIO and the VOLUME setting makes NO difference AND it will POP any time and every time you switch to "RADIO" with the set powered on.

AND, if you do it quickly enough, even after switching OFF the set's "POWER SWITCH" it will do it then as well
(I discovered this while trying to anecdotally/observationally determine if it was going to be some sort of capacitive discharge (or bad cap) or cap/resister "strap" type problem.

I would really be in better shape if I had a darn schematic! But as I wrote I wasn't going to buy a manual for this machine until I felt reasonably certain it was going to be a cost effective move (that the nachine was indeed intact for the most part and wasn't going to die on me after an hour of use).

It was a rescue from the recycling pile! (and being so clean I was apprehensive as to why anyone would discard such a nice radio, old or not)

Marshall

 

[Beosystem10]

That makes it less likely that it's a mains filtering issue then, I was hoping that the motor start cap would take the surge and if that had happened, any switch on spike from the function switch would already have been dealt with. That it pops when it's running and you switch to radio would suggest that this popping is rooted elsewhere,

I wonder, would you be able to make a quick video clip that illustrates the extent of the popping sound? I only ask as that way, I can compare to the pop that comes from both of my 656s when they're switched to radio. One of those is totally original, the other recapped last spring. I know it's a different animal but the a/f section is similar in layout if not in output power.

One last thing, and I've checked but don't see this mentioned yet: Have you tried the set on battery supply and what, if any, difference would that make? If this noise is neither more nor less than the usual pop associated with the amp coming to life, then it would also do this on battery, if we are looking at a mains-related PSU issue, then it wouldn't.

 

[Marshall]

That makes it less likely that it's a mains filtering issue then, I was hoping that the motor start cap would take the surge and if that had happened, any switch on spike from the function switch would already have been dealt with. That it pops when it's running and you switch to radio would suggest that this popping is rooted elsewhere,

I wonder, would you be able to make a quick video clip that illustrates the extent of the popping sound? I only ask as that way, I can compare to the pop that comes from both of my 656s when they're switched to radio. One of those is totally original, the other recapped last spring. I know it's a different animal but the a/f section is similar in layout if not in output power.

One last thing, and I've checked but don't see this mentioned yet: Have you tried the set on battery supply and what, if any, difference would that make? If this noise is neither more nor less than the usual pop associated with the amp coming to life, then it would also do this on battery, if we are looking at a mains-related PSU issue, then it wouldn't.

Hi,
No way to do a video, sorry.

I don't know the answer yet (or even what the problem is) but it is DEFINITELY a problem and enough of an impulse noise to take out a tweeter if it happens enough times

There is no way this impulse noise is by design or normal (WITH the Volume totally defeated); if I had bought this box new back in the day and it did this I'd have returned it! Same as with component Audio; switching inputs with the gain up will result in a nasty pop, but if it does it with the Volume defeated then you've clearly got a problem. And in my case it's only with one mode, "RADIO".

When the set is on the amp chip is powered "ON" so I don't fully understand your question/comment:
this noise is neither more nor less than the usual pop associated with the amp coming to life


The amp is already alive when the set it turned on, yes? Nothing changes that. I've a hunch there is some sort of R/C filter associated with that mode switch as the tuner section will present the biggest draw current wise and my problem will lie there, MAYBE even with the "MODE" switch itself.......but it's going to be on that board in a "who knows where" style as is typically the case with highly populated PC boards....I can feel it ; - )

.......but this is all guessing without a schematic! If aanyone knows where one is I can look at please post.

Thank you for your help!
Marshall

 

[Marshall]

This is the sort of thing that Service Bulletins are made of, although my manuals guy (who does have one complete for this machine) did not indicate that what he has contains any bulletins. I have rarely ordered a manual for any make or model of Japanese gear that didn't include at least ONE tech bulletin, even if it was a printing error or part number/value correction).

I am also thinking along these lines least 4 other people mentioned that their M60s too had one bad woofer. I have yet to get any responses as to which one it was specifically, LEFT or RIGHT but on my machine it was the RIGHT woofer which suffered the open voice coil and which now exhibits the hum, albeit almost imperceptible (and as far as that goes, the extremely low level hum could be purely coincidental and not indicative of any problem, just the proximity of circuitry and the way JVC had to shoe horn the boards in these boxes).

It could even be as I have already mentioned, the mode selector switch itself (arching internally). Without a schematic at this point I can only guess what it is, and isn't "switching" when the different "MODES" are chosen. I would GUESS that power has to be involved and not just signal circuits as the Volume setting has no effect whatsoever. Again, without a schematic I can only guess.

But I just don't know at this point and would prefer the road map a schematic would allow rather than just starting to try and probe things with the box open and the board clipped together with leads (cumbersome to work on apart and I do not enjoy a proper bench, rather a kitchen table!) Plus having to do a whole lot of guessing!

I will try it with batteries as several have suggested; just don't have any here at the house at the moment. Anything is possible but I can't imagine how it will make any difference, but who knows?

Thanks to all,
Marshall

 

[Marshall]

Hello all,
Well duh?! I'm a dumb ass but certainly not a Captain Obvious!
I wrote:
"Is the tuner section powered off electrically when LINE IN or TAPE is in use? (again, the reason why I and everyone need a service manual!)"

Of course it is NOT as you can tape off of either!

This issue almost has to be related to the MODE switch and it's related circuitry (although again, anything is possible) I bet there's a cap or maybe even a cap and resistor in series across that switch in there somewhere.............?

I'm going to have to get a manual (schematic) and hopefully it's marked with some voltage values just as soon as my hand is working again. I just do not have the skill to be able look at a board (populated) and see stuff like that; I can BARELY do it with a road map!.

Spent an hour and a half on the table yesterday getting a chunk of Dupytrin's cut out so I'm pretty much stuck doing nothing for the next few days (which really sucks).

If anyone has a schematic and doesn't mind, please post it so I can start studying it; maybe it won't be that hard to spot the potential problem area(s)

Pardon the even crappier typing; this one hand deal's a bitch!

Marshall