Fujitsu Ten @3000M amp doesnīt power up
Hi @ all.
got this nice Fujitsu Ten amplifier bit it doesnīt power up. It does not even turn on the protection LED.
The SMPS uses a SG3524 controller chip and Iīm not sure if this thing is simply disabled or broken. I already exchanged the chip but stil have the same results. The amplifier is also equipped with a TA7317 protector-chip but as far as i understand the datasheet the TA7317 is only activated once power is connected (in this case when the SMPS powers up).
When the 12Vturn-on Signal is applied the SG3524 gets itīs +12VDC on pin 15 , it also produces 5VDC on the Vref output (Pin16) and I can see the sawtooth on the Ct pin. Sorry but Iīm not too familiar with the SG35.. chips . I measured the voltages (as shown below) on the chip and just want to ask if the chip should turn itīs outputs on or if it is disabled.
3: spikes (see picture)
7: sawtooth (see picture)
Is the chip disabled or should it turn on ? As far as i can understand the (skinny) datasheet the chip is disabled when pin 10 is greater than 2VDC. As there is only 0,001V it should not be disabled.
Thx for any help.
The SG ICs produce output when the voltage on the compensation pin is above the bottom of the sawtooth waveform. The bottom of the sawtooth is ~0.75v. The input to the error amp (pins 1 and 2) are causing the voltage on the compensation terminal to go to ground and is shutting down the output. Pin 2 must be higher than pin 1 for the chip to drive the compensation pin high.
Do whatever is necessary to force the error amp to go high (force pin 1 lower or pin 2 higher -- whatever is easiest/safest). The power supply should then power up and you can check to see if there is truly a problem (pulling too much current, DC offset...). If there is no problem with the audio section, then there is likely a problem with the protection circuit itself.
Do this with some sort or power supply current limiter.
If you install the power supply IC in a socket, it's easy to leave the error amp pins out of the circuit (bend them so they don't go into the socket). This allows you to apply any voltage you like to them without fear of damaging the circuit driving them.
thx fpr the info. I already installed the socket so I can quckly test this .
I always use a current limiter when fixing amplifiers because I like my face as it is :-)
I īm more familiar with the TL494 and know that the error amps are used to shutdown the SMPS and just wanted to make sure that the 3524 is used the same way. i already checked the amplifier section for shorts and couldnīt find any. With your help I can probably trace the fault back and find why Pin 2 is lower in voltage than Pin 1. Maybe itīs one of the capacitors from the startup-delay curcuit or something.
I let you know what happens.
setting Pin2 to 5V doesnīt do the trick. The smps starts (I can hear the transformer) but is shut down again after 0.5 seconds. When it is off again I still have a higher voltage on pin 2 than I have on pin1 .
This amp is a tricky son of a...... , pin 1 is controlled by an Op-Amp (njm4558) . The OP Amp is not powered by the 12V source, itīs power pins are connected to Zener-Diodes that are connected to the output voltage of the smps. I īve drawn a short picture to see how pin1 and pin 2 are connected.
Now what confuses me is that although the smps does not generate any output voltage, the OpAmp delivers 8V output voltage (measured to chassis GND). Additionally, the 2SC1815 is active. If I disconnect the 22kOhm base resistor the voltage at Pin2 rises to 2,5V , as i assume it is supposed to.
Also, there is a 4-3-2 channel switch (already checked that the switch is operating properly) that activates small relays in the music section but this switch is also connected via a 22kOhm resistor to the 2SC1815.
I will check the transforme coils for shorts (primary to secondary coils) . I will try to finish the drawing with the 4-3-2channel switch , but as far as I understand this the 2SC1815 can only be fully opened or closed, causing the voltage on pin2 to be either 2V or 2,5V. So if anyone could tell me how to continue on this amp ......
Ok, I connected +/-24V to the amplifiers and fed a sine to the inputs. the OpAmps work fine and all 4 power-amps produce a clean output signal . So I assume the amplifier curcuits are all fine.
but the TA7317P doesnīt activate the output-relays.
Voltages on the TA7317P
Isnīt the TA7317 supposed to be powered with the same power supply than the amplifiers ?
This IC grounds one terminal of the relay. The other side of the relay will be connected to a power supply rail (possibly via a resistor or zener).
Measure the voltage across the relay coil. It should be near the voltage rating of the relay coil. If not, determine why the relay is not getting voltage to the side of the coil that's NOT connected to the IC.
If the relay has sufficient voltage across its coil, double-check the solder connections on the relay. They often fail on single-sided boards.
If the voltage across the coil is sufficient and the solder connections are good, the relay should be engaged. If it isn't clicking when the amp is powered up/down, then the coil may be open (not likely since the voltage on pin 6 is above ground). If it does click, the contacts may be damaged.
I couldn't find a datasheet but this site has the pin configuration and internal schematics. If you're able to find a datasheet, please post a link to it.
I checked the relays and took em off the curcuitboard and both are fine. I guess without the proper chematics it will be hard to repair this amplifier, itīs very different from most of the stuff i ve seen in the past .
As far as I can trace the curcuit lines back the relaysī coils are directly connected to pin 6 of the TA-IC, but the other relay-coil connector doesnīt have a direct connection to V+ . Across the coils I have exactly 0V. I will have to draw down how the TA7317 is connected.
Could it be that this amplifier only works if all metal parts ( partial aluminum blocks , folded sheets, etc) are mounted to the main heat sink ?
You shouldn't have to completely reassemble the amp for it to work but you have to make sure all electrical connections are reconnected.
It's strange that pin 6 is above ground (1.8v) and you have no voltage across the coils. It's unlikely that anything else is connected to pin 6. How can there be voltage if there is no voltage on the relay coils?
Measure the resistance across the coil pads (on the circuit board) and make sure that the reverse diode is not shorted (if there is a diode).
If there is no short across the coils (on the board), you need to determine why voltage is not reaching the coils. If pin 4 of the protection IC is connected to ground, the only thing the chip can do is ground the relays. This means that the relays have to be fed from a positive rail or off of the B+ line.
reverse diode is ok , the relays show ca. 80 Ohms . Pin 6 is also connected to the "power" LED . I will try to make a schematic of the smps and the protection curcuit before I continue . The TA also has connections to the SMPS parts . I will also make two bigger pictures of the amp, maybe you can recognize something to look for.
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