Audio System Twister F4-560 - Troubleshooting

[Piasa]

I´ve got a Audio System Twister F4-560, the previous owner wrote that it switched from red to green without any reason.

Missing screws and after disassembling the PCB I saw that somebody else worked on the Amp before.

The transformer had scratch marks at the primary side middle pins.

Q3 and Q4 were replaced.
Output 2 "Bridge +" was "pushed" so that the solder connection broke at the top side.
The Case was pushed into the PCB which damaged the LED´s On and Protect.
The biggest damage was caused by leaking electrolytic capacitors (C42, C69 Input capacistors; The link capacitors C38, C39, C40, C41, C65, C66, C67, C68) that burned/corroded the pads underneath. That caused most probably the green/red switcheroo. I didn´t switch it on with the damaged capacitors.
After desoldering and cleaning the PCB I coated the area around the contacts with a thin layer of lacquer for further protection.


I switched it on, only protect lit up. No life sign from the power supply.
I wasted a lot of time on the protection circuit, in the end I tried everything I could think of.


LM339 (U10) Quad comparator


Triggered the comparator outputs, Replaced the LM339, measured every SOT23 (2Gp - BC850C NPN, 4Gp - BC860C PNP) transistor out of circuit and checked the resistors on the paths.
I used the schematic of the F2-190, backtraced as far as I could.


In the end I switched the Remote after the B+ on. That "solved" the problem. No Amp before had a problem with Remote and B+ on at the same time.

Should I look more into this?


The Amp switched on (Consumption 1,30A), it build rail-voltage up. (+/-36V)

Bias-Voltage at

DZ3: - 6,93V

DZ4: + 6,99V


Pre-Amp voltage -18,50V and +18,53V at the transistors Q75 and Q76.

 

[Perry Babin]

This is good reminder for those working on GT trading amps. I didn't see many (any?) Twister amps here but Boston and Polk(?) had amps that used similar circuits and wouldn't turn on when remote and B+ were applied at the same time.

If the boards don't have GT Trading on the board, the layout with the op-amp very near the outputs and the bias pot is a good way to identify the GT Trading amps. This is for a Boston amp.

 

[Piasa]

Audio System Amps are build pretty similar in shape and design of the channels and drive circuits.



I used this schematic as a reference. Picture 2 is transcribed to the notation of the F4-560

AUDIO SYSTEM F2-190 Service Manual download, schematics, eeprom, repair info for electronics experts


Power Supply FET´s (Q17, Q18, Q19, Q20, Q21, Q22)

Marking: 75343P = STP60N55F3 (80A, 55V, 9mOhm) --> Discontinued

STP75N75 (75A, 55A, 9mOhm)?

AUIRF3305 (140A, 55V, 8mOhm)?


Rectifiers (D1, D2, D3, D4)

China STPR15


Output-Stage (Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, Q12, Q13, Q14, Q15, Q16)

Left side of channel (N-Channel)

IRF540A (100V, 28A, 52mOhm) --> Discontinued
FQP33N10 (100V, 33A, 52mOhm)

Right side of channel (P-Channel)

SFP9540 (100V, 17A, 0,2Ohm) --> Discontinued

Infineon IRF9540NPBF (100V, 23A, 0,117Ohm)

Vishay IRF9540PBF-BE3


Transformer (Measured with Agilent U1733C)

Primary From top to bottom - Red, Yellow, Red, Yellow

Z= 0,3515 Ohm
L= 56,10 uH
C= 453,1 uF
R= 0,0316 Ohm

Z= 0,3470 Ohm
L= 54,91 uH
C= 457,7 uF
R=0,0327 Ohm

Secondary From top to bottom - Red, Yellow, Red, Yellow

Z= 2,927 Ohm
L= 464,3 uH
C= 54,75 uF
R= 0,0473 Ohm

Z= 2,882 Ohm
L= 458,0 uH
C= 55,45 uF
R= 0,0462 Ohm

Potentiometer

TRM1: 2,256kOhm
TRM2: 2,531kOhm
TRM3: 2,638kOhm
TRM4: 2,779kOhm

Fan 1/2: TOP MOTOR DF1206SH (DC12V, 0,20A, 2,4W)

 

[Perry Babin]

I use PDF-XChange Editor to markup diagrams on a copy of the original PDF file. The file stays clean and neat and easy to backup to ensure that it's not lost.

 

[Piasa]

Thank you for the tip Mr. babin, i prefer to write on real paper, still downloaded the XChange Editor.

 

[Piasa]

Audio System and STEG is a "german branch" of GT trading.


"Gladen German Technology" is somehow part of this too.