LTO PS 4LA Powerred Speakers - Tweeter Audio Low

[willis6732]

Hello, I have two of these speakers with the same Prioblem. The tweeter volume is very low. I believe it happened after running them too loud.


There is a lightbulb on the tweeter output i tried shorting and no change.

The tweeters measure 6 ohms and it seems to play loud if i plug them into an alternate amplifier

There are a couple resistors and diode getting really hot in the mute circuit...

At the bottom left of image. R17 gets the hottest. Over 70 deg C
Z1 and R7 next to that get hot as well. Zener tests ok
I measured the Q1 Transistor in circuit and it wasnt shorted. maybe i should take it out to check...


Wondering If i should blindly change the LM3886TF on the tweeter side, Or is something going on with the mute circuit...


Thank you
Kevin


Schematics
https://www.electronica-pt.com/esque...o-ps4la-36441/

[petehall347]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

mute would affect the low as well .
check voltages at the ic

[willis6732]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

Hello, thanks for the push forward.

I have the IC voltages and the voltages around R17.
R17 over 100 Deg C...
Z1 and R7 get hot as well.


Q1 on the bottom left has less than 1V difference between base and collector. Should it have -27.8v on the collector and emitter with only 1v Difference on the base?? Check transistor out of circuit?

THanks
Kevin

[petehall347]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

r17 is running at 0.77284 watts .. what wattage resistor is fitted ?
yes check q1 in circuit first to see if shorted . if it is then remove and check again .

[willis6732]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

r17 is running at 0.77284 watts .. what wattage resistor is fitted ?
yes check q1 in circuit first to see if shorted . if it is then remove and check again .

Took out the transistor and it seems fine.

Its a PNP and -.8V on the base so i think thats right that its on... But how then do you get the base voltage back up.

All the resistors in that areas measure fine. They are just tiny 1/4W guys.

I was going to trying disconnecting the mute pin on the Tweeter driver but its hard to get too, ill have to cut the pin off if i want to test that...

[stj]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

you never mentioned the bass - i assume it's fine
looking at the schem i cant see anything other that the amp chip or bad soldering on it or something related to it.
it's the type of package that kind of attracts cracked solder joints.

try swapping it around with one of the others - that way you arent buying a relativly expensive chip for nothing

[willis6732]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

Hey having some success...

Ive disconnected the mute circuit and the bass works fine, so continuing testing without it...

See photo:
Ive disconnect the +VIN from the Tweeter amplifyer chip by disconnecting the cap and resistor next to it.
If i connect the +VIN before the 220P Cap (right at the main input) i get louder volume but sounds like crap.

I found C18 (10P) which connects the In to the Out is no good...

[willis6732]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

Ive just recived these in the mail. Im more incline to just pop one of these in, But with the Crossover being messup up i need to make one or figure that out.

Never did that before..

Any suggestions? Can i just put a Capacitor in Series or does it need a coil too?

[willis6732]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

you never mentioned the bass - i assume it's fine
looking at the schem i cant see anything other that the amp chip or bad soldering on it or something related to it.
it's the type of package that kind of attracts cracked solder joints.

try swapping it around with one of the others - that way you arent buying a relativly expensive chip for nothing

So i believe the whole problem with the low audio in the tweeter is in the "crossover"(?) area.

THe capacitor and resistor seem fine, so i would just like to bypass and add my own crossover if possible?

If i want to bypass this area and add my own crossover, Do i need to know the freqency of the tweeter. I couldnt find aything in the schematics, just that it is a 15W 8Ohm Speaker. Perhaps close is good enough?

I wouldnt mind just odering one on aliexpress. I found this one quite. Anything i should avoid or look for when choosing?

https://vi.aliexpress.com/item/10050...d=UkKzTf2aY5Kl

[stj]

Re: LTO PS 4LA Powerred Speakers - Tweeter Audio Low

when buying crossovers it's important to get the right frequency's to match the speaker range

[willis6732]

I ended up just changing all the ceramic capicitors on the Tweeter Side. That worked and got the sound going!!

It doesnt seem crazy loud but the sound is back and the high/low sound pretty balanced...