Technics SU-G75 tweeter audio comes in/out

[cptsomeone]

Technics SU-G75 receiver with Technics SB-A15 speakers. The copper cable runs from speaker to receiver are as short as possible.

For some reason, audio seems to come in/out of the tweeters of the speakers every now and then... but it appears to be an issue with the receiver than the speakers in my opinion. Only bass frequencies are coming through in this situation. Initially it was only on the left channel speaker, and it now appears to be happening with BOTH (not simultaneously) after a second deoxiting.

If I crank the volume dial past -30db, or do so with the remote, the tweeters come back; either briefly or for the rest of the listening session. I can also lower the volume back down without it (normally) losing the tweeters again.

Audio input is CD, purely "digital" in receipt to the receiver.

Already opening the unit up and deoxit'd main contacts for the front panel, the pots for the Balance and Volume knobs... (twice now)... also put some Deoxit on the speaker contact points inside the unit at the back. Sadly no lube on hand sorry. Also replaced the speaker wire for both speakers, no difference.

Blanking on exactly what the issue is here... It's a very simple unit internally I feel, I really like the design, and it outputs clean good audio for a stereo speaker setup; perfect for music, movies, games, etc. I'd hate to have to get rid of it; I have a surround unit I can test with to truly rule out the speakers, but I'd rather that use it's own set of 5.1 speakers.



See photos for internals, I don't see any caps needing replacement or leaking. The unit was mildly used by the previous owner, and this issue seems to have appeared only recently. Unit was always stored inside, never outside. It's very very clean.

Thank you!

 

[SVI2004A]

Dry joints in tone (treble) control or pcb plugs to main board?

 

[cptsomeone]

Dry joints in tone (treble) control or pcb plugs to main board?

haven't cleaned the treble/bass controls but odd it would be the source of the issue.

I have successfully reproduced resolving the issue every time by setting audio past -30db. Also it happens regardless of using the physical knob or remote...
Also it does seem to cut in and out rarely afterwards...

Argh!!

PCB Plugs to main board (front panel > main board) I did deoxit those, unless there's others?

 

[SVI2004A]

The speakers may have a self resetting overload on the tweeters - these can cause this issue too

 

[cptsomeone]

Hi there and sorry to bump an old thread but I finally have an update.

I've fully Deoxit'ed both input boards, all the connection clamps on the speakers themselves, and confirmed everything is working. Everything was Deoxit'ed, all over!!
Brand new pure copper speaker wire (from PrimeCables.ca).
Changed to a newer more modern amp, Pioneer VSX-D510 5.1 unit (but currently setup as Stereo).
Also changed to Digital Optical Input

Couple things have jumped out at me:

1. There *is* a thermal protection unit present... but it's intended to protect the unit if things get too hot, from too high volume, which is not the issue here
See photo:


2. The issue now seems to be mitigated a bit, but is still present.

Now what normally happens is: Turn the amp on, play media, the tweeter and mids will be muffled or off, but pushing the volume up to -30db pops them right back into play (that's way too loud though for normal listening).

So I'm just... confused what to do next to resolve this so that *every* time I turn the amp on, the speakers JUST WORK.
And that there's no more dropouts *during* listening, so that I don't have to fiddle with settings and annoy my guests.
I have isolated the issue to the speakers, and NOT the amp(s).

The ONLY possible issue left would be cold solder joints? See photos.

I am otherwise stumped. Is this perhaps why older amps would *pop* when you turned them on, to prep the speaker into working?
Thank you for any help from anyone.

 

[cptsomeone]

Sorry to bump an old thread, I can't edit my old posts, but this is actually an issue with the SB-A31 speaker module as shown in the later photos. It's an issue with the thermal protection module, effectively it's failing. I'm currently trying to resolve replacing all the resistor/capacitors to ensure the unit functions perfectly, just wanted to provide further information for anyone that comes across this. I'll be making a further post to discuss more in depth.

 

[Wishbone 21]

Technics SU-G75 receiver with Technics SB-A15 speakers. The copper cable runs from speaker to receiver are as short as possible.

For some reason, audio seems to come in/out of the tweeters of the speakers every now and then... but it appears to be an issue with the receiver than the speakers in my opinion. Only bass frequencies are coming through in this situation. Initially it was only on the left channel speaker, and it now appears to be happening with BOTH (not simultaneously) after a second deoxiting.

If I crank the volume dial past -30db, or do so with the remote, the tweeters come back; either briefly or for the rest of the listening session. I can also lower the volume back down without it (normally) losing the tweeters again.

Audio input is CD, purely "digital" in receipt to the receiver.

Already opening the unit up and deoxit'd main contacts for the front panel, the pots for the Balance and Volume knobs... (twice now)... also put some Deoxit on the speaker contact points inside the unit at the back. Sadly no lube on hand sorry. Also replaced the speaker wire for both speakers, no difference.

Blanking on exactly what the issue is here... It's a very simple unit internally I feel, I really like the design, and it outputs clean good audio for a stereo speaker setup; perfect for music, movies, games, etc. I'd hate to have to get rid of it; I have a surround unit I can test with to truly rule out the speakers, but I'd rather that use it's own set of 5.1 speakers.



See photos for internals, I don't see any caps needing replacement or leaking. The unit was mildly used by the previous owner, and this issue seems to have appeared only recently. Unit was always stored inside, never outside. It's very very clean.

Thank you!

Hi,so I no this is old,but I just got this unit for $30.00,powered up with no sound the guy that sold it to me,has remote, so I watch a YouTube video,and this English fella says,that these intregated Technics are known for dry solder joints,so I re-soldered some and it plays amazing,lot of power,I like it so much i bought the St-k55 tuner that normally went with this unit for $20.00. Today.its not my main unit,I have others,pioneer sc-07 ,which was over $2200.00 back in 2012 and it sounds just as good.