Yamaha M-4 Speaker B Output Issues

[44100_Hz]

Hello! Long time lurker, first time poster.

I recently purchased a Yamaha M-4 which I've been running through the speaker B output as the speaker A button was stuck (but not engaged). I've been experiencing output issues where the audio will get extremely quiet in one or both channels or become staticky. Temporarily increasing the volume above listening level seems to reset it back for a little while.

However, now that I've got it open to fix the speaker A button and replace the lamps, I'm able to audition it with speakers connected to the speaker A terminals and . . . no issue. I'm assuming this narrows down the areas in the signal path that could be the issue, but I'm looking for some perspective on where to start. Thanks so much for any help you can provide!

 

[avionic]

Welcome aboard 44.1Khz

You need a new protect relay for SPK B.. I would recommend replacing both while your in there.

 

[avionic]

Drop in replacement..

https://www.digikey.com/en/products...83171?s=N4IgTCBcDaILIE0AsBaADGFARAwgRggF0BfIA

 

[avionic]

Temporarily increasing the volume above listening level seems to reset it back for a little while.

Dead give away for fouled relay contacts.

 

[44100_Hz]

Welcome aboard 44.1Khz

You need a new protect relay for SPK B.. I would recommend replacing both while your in there.

Thank you so much (and for the link as well, since that was pretty much guaranteed to be my next question)!

 

[avionic]

Gett'r done..

 

[44100_Hz]

Gett'r done..

New relays have arrived, leaving me with what I suspect is a fairly basic follow-up question: the existing relays appear to have 8 connections to the PCB, but the replacement relays (MY4-02-DC12) have 14 terminals. I had seen your advice in a previous thread to clip unnecessary terminals, so now I'm trying to figure out which of these are the unnecessary ones. Comparing the service manual to the new relay circuit diagram, my assumption would be that I'm keeping 5, 6, 7, 8, 9, 12, 13 and 14, and bridging 5 to 6 and 7 to 8. Is that correct? Thanks again for all your help!

 

[avionic]

Yes.

 

[44100_Hz]

Yes.

Awesome. Thank you!

 

[44100_Hz]

UPDATE: I was able to modify and install the two new speaker relays. Thanks again, avionic, for your help and advice. Everything's working and sounds great!

Had two questions (with pictures) that I hope don't indicate I'll have to take everything apart again:

1) When I removed the old relay, I noticed that it had some sort of coating over the base of all of the contacts (both removed and retained). I prepared the new relays by filing the unused pins down to flush with the plastic backing, but I didn't use any coating on them. Will that be something I need to remedy for safety's sake? If so, what should I use? I'd estimate that the removed pins have at least 1 mm clearance from the board surface installed.

2) I used rosin-core solder, and swabbed the connections and areas around them with 91% isopropyl rubbing alcohol on a Q-tip afterwards. However, I noticed that the surface of the PCB was dull after the alcohol dried, including when I tried on a spot away from the area where I had been working. Does this reflect incomplete/incorrect cleaning on my part, or is there some sort of lacquer on the board? Trying to figure out if there's anything additional I need to do there to make sure I don't cause any future damage.

Thanks!

 

[bberkom]

I wouldn't worry about the pins on the relay, and the iso just dulled the solder mask layer on the PCB. I use alcohol to clean too, and it won't hurt anything.

 

[avionic]

but I didn't use any coating on them. Will that be something I need to remedy for safety's sake?

No

 

[avionic]

The removal of the glossy conformal coating is no problem . I usually remove all of it. Don´t sweat it. It is not and issue.

 

[44100_Hz]

Awesome. Thanks for the reassurance, bberkom and avionic!

 

[Asmodeus2112]

Hello! Long time lurker, first time poster.

I recently purchased a Yamaha M-4 which I've been running through the speaker B output as the speaker A button was stuck (but not engaged). I've been experiencing output issues where the audio will get extremely quiet in one or both channels or become staticky. Temporarily increasing the volume above listening level seems to reset it back for a little while.

However, now that I've got it open to fix the speaker A button and replace the lamps, I'm able to audition it with speakers connected to the speaker A terminals and . . . no issue. I'm assuming this narrows down the areas in the signal path that could be the issue, but I'm looking for some perspective on where to start. Thanks so much for any help you can provide!

Hey, congrats on the fix. Post some pictures of your M-4 please? It looks nice from what little can be seen from the pics you posted already

 

[44100_Hz]

Hey, congrats on the fix. Post some pictures of your M-4 please? It looks nice from what little can be seen from the pics you posted already

Happy to oblige! Still not fully reassembled as I'm trying to figure out how to deal with the dust (while protecting the volume pots that appear--fingers crossed--to be in pretty good shape) and need to source a new screw for the switch cover. So far, have replaced the speaker relays with considerable help from avionic; replaced the lamps and bulb covers with new ones ordered from dgwojo; fixed that stuck speaker A button; and adjusted power supply voltage, idling current and DC offset back to specs.

 

[Asmodeus2112]

Happy to oblige! Still not fully reassembled as I'm trying to figure out how to deal with the dust (while protecting the volume pots that appear--fingers crossed--to be in pretty good shape) and need to source a new screw for the switch cover. So far, have replaced the speaker relays with considerable help from avionic; replaced the lamps and bulb covers with new ones ordered from dgwojo; fixed that stuck speaker A button; and adjusted power supply voltage, idling current and DC offset back to specs.

Thanks! I'm half way into cleaning up and recapping my second M-4. I always enjoy seeing pics of other ones.