Old Technics amp 'problem'...

[ellal]

I have an old Technics amp (SA-GX190) that has suddenly gone into steroid mode!

The display now shows that a 'loudness' option is activated, and the volume/bass response certainly gives a total change in output!

The problem is I can't find anything on the amp/remote to control or turn on or off the 'loudness' feature.

Whatever audio source I choose makes no difference, and a power off has done nothing.

Any ideas as to what I can do to solve this, as google so far hasn't come up with anything that works.

 

[RandomGrinch]

The display now shows that a 'loudness' option is activated, and the volume/bass response certainly gives a total change in output!

Can you post a pic of the display?

That definitely seems a bit odd, as I can't find any references to loudness in the manual.

 

[RandomGrinch]

I've just found a similar question - sadly no answer...

Technics Loudness Display

My ancient Technics SA-GX190 still sounds great, especially since I added the tall Definition speakers. Only thing is I just noticed that the display now shows the word "Loudness". Pretty sure it was not there previously and there is no mention of this function in the Operating Instructions...

audiokarma.org

But most of the questions are similar to what I would have asked next!
I.e.
Have you recently changed speakers (caused an overload)?
Or without knowing it, pressed a couple of buttons together on the remote at the same time - if I hold down one button on my Fire stick remote, my LG TV enters an engineering mode that resets the system to the default audio and video settings.
My five year old discovered this. I was both impressed and upset that I had to change all my settings back!

 

[ellal]

Can you post a pic of the display?

That definitely seems a bit odd, as I can't find any references to loudness in the manual.

See pic below (apologies for the quality)

Also I saw that link, but as you say no answer.

And I haven't changed a thing as regards the setup and didn't use the remote to power on or change any settings.

Edit: But to give you an idea about the audio output change, whereas a 6 on the volume would normally fill the room a 4 now does the job.
And I can reduce the bass using the relevant knob, but just want to know why this trustworthy old amp is having a mid life crisis!
(It still knocks the socks off most new setups I've heard soundwise btw)

 

[Odds]

Buy a can of contact cleaner and spray everything you can see.

Or.

Sea Kelp from Audio Karma.org

 

[RandomGrinch]

As with all internet advice, I could be completely wrong...

Apparently the SA-GX170 is almost identical to yours - the service manual is easily found (there is only a 4 page addendum updating the schematic to a GX190).

Looking at the schematic, the tone amp circuit is a completely self contained system, only the treble/bass/balance knobs effect it.
No other electronics are involved - i.e. remote control button presses won't effect the tone.

Which led me to the main controller IC...

Which has a loudness pin, that shouldn't be connected.

So, I'm guessing that there could be a slight short to the pin/PCB corrosion, or something internal to the IC may be a bit squiffy!

The only thing I can suggest, without delving into the electronics - unplug the amp, and short the plug pins on a piece of metal (screwdriver etc.), and leave it like that for a good while.
It's just to try and drain any capacitors of their charge, and hopefully allow the IC to reset itself.

Service manual attached...

 

[freddiemercurystwin]

I'd just buy another off ebay if you're that attached to it, otherwise look on it as an opportunity to upgrade.

Technics SA-GX190 for sale | eBay

Find great deals on eBay for Technics SA-GX190. Shop with confidence.

www.ebay.co.uk

 

[Mottie]

Here’s one but the postage costs kills it for me…..a fiver!

 

[ellal]

As with all internet advice, I could be completely wrong...

Apparently the SA-GX170 is almost identical to yours - the service manual is easily found (there is only a 4 page addendum updating the schematic to a GX190).

Looking at the schematic, the tone amp circuit is a completely self contained system, only the treble/bass/balance knobs effect it.
No other electronics are involved - i.e. remote control button presses won't effect the tone.

View attachment 325003
Which led me to the main controller IC...

View attachment 325004

Which has a loudness pin, that shouldn't be connected.

So, I'm guessing that there could be a slight short to the pin/PCB corrosion, or something internal to the IC may be a bit squiffy!

The only thing I can suggest, without delving into the electronics - unplug the amp, and short the plug pins on a piece of metal (screwdriver etc.), and leave it like that for a good while.
It's just to try and drain any capacitors of their charge, and hopefully allow the IC to reset itself.

Service manual attached...

Thanks for that.

Will try the non invasive measure first!

 

[NewAce]

Hey ellal, have you been successful with getting rid of the "loudness" label yet? I had the exact same problem on my SA-GX170 for the last few months and after reviewing the service manual on pages 13 and 18 (of the pdf), I found out how to factory reset the main computer and it got rid of the loudness light for me. It requires steady hands, but what you do is locate pin 50 on the computer within the amplifier. This is the reset pin. Then what you need to do is use a wire and ground the pin for a few seconds (touch the other pin to the heatsink nearby). If you are working on the amp while it is turned on, the amp will shut off while you do this and reboot after you are done holding the wire in place for some time. I have no idea how the amp ever got into "loudness" mode, perhaps a power surge or some electrical anomaly caused it to happen, but at least it's gone for now. Looking inside of this amp really gave me an appreciation for old amps like this. I've recently tried to work on a modern Pioneer amp for a friend and there is no service manual or documentation to help you fix it.

 

[RandomGrinch]

I found out how to factory reset the main computer and it got rid of the loudness light for me

Brilliant, well done!

. I have no idea how the amp ever got into "loudness" mode, perhaps a power surge or some electrical anomaly caused it to happen, but at least it's gone for now

It's a little bit poor, the loud pin is just floating, and not tied to a rail - some stray capacitance or corrosion may be all it takes to turn it on...

It requires steady hands, but what you do is locate pin 50 on the computer within the amplifier.

It may have been slightly easier to find the next solder pad along the track, rather than try and ground the pin itself - there would be a far lower risk of anything going wrong.

If you are working on the amp while it is turned on, the amp will shut off while you do this and reboot after you are done holding the wire in place for some time.

I had noticed the reset pin, and it's connection to standby, which was why is suggested shorting the plug pins, but now we know the system can do a full reset on that pin, I'm wondering if a (very) long press on the standby button (when the amp is on), may initiate a reset? - the circuit diagram seems to show that it "could" work that way.

 

[NewAce]

It may have been slightly easier to find the next solder pad along the track, rather than try and ground the pin itself - there would be a far lower risk of anything going wrong.

I never even noticed that, yes you could use the third solder pad directly right of the screw below the chip to do this too.

I had noticed the reset pin, and it's connection to standby, which was why is suggested shorting the plug pins, but now we know the system can do a full reset on that pin, I'm wondering if a (very) long press on the standby button (when the amp is on), may initiate a reset? - the circuit diagram seems to show that it "could" work that way.

I'll have to program some stations into the tuner and try this tonight.

 

[NewAce]

After trying to hold the power button down for a very long time, I can't seem to get it to factory reset that way, so the "grounding the reset pin" method seems to be the best option for resetting the computer.