Audio System Twister F6-380

[Achim1409]

Hello,


i got this amp. If i connect power, it shows over the LED´s normal power up, but
the Power Supply is not working.


Found: U7 SG3525 has no power at Pin 15.
I cannot find a direct connection to any Transistor, resistors arround the U7 all in range, diodes and transistors measure ok in circuit.
For me is strange, that the OP-AMp below (U14 LM358D) has also no supply voltage.
Pin 4 from U14 is directly connected to Pin 15 U7.


If i measure from Bat - to Pin 15, there is 0V, if i measure from Bat+ to Pin 15, i measure supply voltage.


Greetings


Achim



Maybe somebody has advice where to look?

 

[Osvaldo de Banfield]

Several of those amps have an independent power terminal for the logic, sometimes called "remote" or the like. Did you find this terminal? Did you power this terminal?

 

[ultra]

Pin 4 of U14 is the negative supply for the comparator (it should be grounded in this amp).
As for the 3525, did you check if there is any low ohmic resistor feeding pin 15 ?

 

[Achim1409]

Osvaldo, remote is connected.
Only high value resistors. 3.9k and higher. Three ground caps are connected and a zener. But all measure ok.

 

[Osvaldo de Banfield]

The PCB is double layer or multiple sandwich?

 

[Perry Babin]

The power supply configuration may be like this amp.

 

[Achim1409]

I have this diagram, on this plan, U14 is missing, and Pin 15 is not direct connected to Q26. or i canot measure the connection.

 

[Osvaldo de Banfield]

Consider a blown PCB trace inside the sandwich. Usually a bubble is made in the substrate.

 

[Achim1409]

Ok, so if there is i burned trace inside the pcb, it would be difficult for me, to find the right connection. I think, there is a leaky diode or something, which is pulling V+ down.

 

[Bertje]

It's just dubble layer pcb, nothing special. Maybe a trace under a big capacitor or glue. It's not in mute / protection mode?

 

[Achim1409]

No, its not in protection. The Amp is on, no Mute. But no railvoltage because The sg3525 dont get PIN 15

 

[Achim1409]

So, i tested, made i direct connection between Pin 15 and the collector of Q26. Amp builds up railvoltage...

 

[MarioRestucci]

This is not multilayer PCB, simple dual layer...
The remote connection pass trough a couple of transistor and the green led...
If the Green led is defective, the amp does not turn on and the power supply don't work...


Study the F2190 schematic well, I assure you that, by identifying the same transistors (which are screen-printed differently) on your model, you will solve the problem.
I had the same problem with a F2-500 and thanks to the schematic and a bit of effort, I managed to solve the problem, it was more stupid than you think.

 

[Achim1409]

Hello Mario,
yes, the led´s are ok and working. If i connect the remote, the green led is on. In this case the power supply is not working. I connected a cable between the transistor and pin 15, now the amp powers up and 4 from 6 channels are working. The last two channels dont get a signal from rca. Problem is, that the last to channels going to a sound ic (BH3852S)

I think there are some corrosion damages, so i will investigate a little more.

 

[Achim1409]

So, the other two channels also working. My mistake, wrong settings of the switches. I leave it like this.