Hi guys
I'm trying to fix a avt150. It's blown the tda7293s and the 2.2r resistors.
Which seems to be a common thing. The resistor had up to 16k.
Did an initial check but blew the new chips a 23volts on a variac. The chip popped over the signal in pin. I'm obviously missing something.
Anyone else had this problem.
Thx
I'm trying to fix a avt150. It's blown the tda7293s and the 2.2r resistors.
Which seems to be a common thing. The resistor had up to 16k.
Did an initial check but blew the new chips a 23volts on a variac. The chip popped over the signal in pin. I'm obviously missing something.
Anyone else had this problem.
Thx
Common? If an AVT blows up it is likely this, but most do not blow up.
The 2 ohm resistors are limiters in the low voltage supplies, and are not usually involved in blown 7293s. Leave the power ICs out and make sure those low voltage circuits are right before moving on.
Always work with no speaker load until you know the amp is stable and not making DC.
The power modules have two connectors, the three pin carries the power rails. NEVER connect or disconnect the power modules if there is any charge in those power supplies. ALWAYS check for voltage on the pins before plugging it in.
If one power module blows, replace both. One bad one stresses the other "good" one. Note their outputs are hard-wired together.
I forget which is which in the AVT series, but in some the heat sink is grounded to chassis, in others the heatsink is insulated - mounted to the plastic fan housing. The heatsink tab on the IC is hot, and so must be insulated from grounded heat sinks. If that is yours make sure your insulating wafer is intact.
The 2 ohm resistors are limiters in the low voltage supplies, and are not usually involved in blown 7293s. Leave the power ICs out and make sure those low voltage circuits are right before moving on.
Always work with no speaker load until you know the amp is stable and not making DC.
The power modules have two connectors, the three pin carries the power rails. NEVER connect or disconnect the power modules if there is any charge in those power supplies. ALWAYS check for voltage on the pins before plugging it in.
If one power module blows, replace both. One bad one stresses the other "good" one. Note their outputs are hard-wired together.
I forget which is which in the AVT series, but in some the heat sink is grounded to chassis, in others the heatsink is insulated - mounted to the plastic fan housing. The heatsink tab on the IC is hot, and so must be insulated from grounded heat sinks. If that is yours make sure your insulating wafer is intact.
Thanks Enzo
I think it's the way They link that's confusing me. I have the schematic. But the 7293's are a different beast.
I'm going to retest the voltages. Would you remove the chips from the boards and test voltages at the pin outs?
I'll check and post my findings.
I think it's the way They link that's confusing me. I have the schematic. But the 7293's are a different beast.
I'm going to retest the voltages. Would you remove the chips from the boards and test voltages at the pin outs?
I'll check and post my findings.
You can buy whole new modules, but I always replace the chips. The little caps on the module boards never seem to be bad, and unless the copper is burnt of the board, a new 7293 does the job.
The amp is happy as can be with the modules unplugged, so you can operate the amp without them to verify everything else is OK. If you want to plug in empty modules to see if voltages are there, go ahead. I'd probably just probe the cable connector myself.
The same board the 150 uses is also used for the stereo 275 model. The schematic has a box for each model listing which links, resistors, and caps are to be installed or left out. So keep those in mind when trying to read the drawing.
Make sure zobel resistors R110,112 are not open. And speaker return resistor R111, is it OK?
The amp is happy as can be with the modules unplugged, so you can operate the amp without them to verify everything else is OK. If you want to plug in empty modules to see if voltages are there, go ahead. I'd probably just probe the cable connector myself.
The same board the 150 uses is also used for the stereo 275 model. The schematic has a box for each model listing which links, resistors, and caps are to be installed or left out. So keep those in mind when trying to read the drawing.
Make sure zobel resistors R110,112 are not open. And speaker return resistor R111, is it OK?
Check r110 111 112 all ok
The voltages check on the board pins.
C230. C189
1.. 2mv. 2mv
2.. 88mv. -78mv
3.. 2mv. -49mv
4.. 6v. 6v
5.. 2mv. 2mv
6.. -1mv. -2mv
7.. 0mv. -1mv
8.. -1mv. -2mv
Each three pin has N. -49 +49.
The voltages check on the board pins.
C230. C189
1.. 2mv. 2mv
2.. 88mv. -78mv
3.. 2mv. -49mv
4.. 6v. 6v
5.. 2mv. 2mv
6.. -1mv. -2mv
7.. 0mv. -1mv
8.. -1mv. -2mv
Each three pin has N. -49 +49.
New tda's installed haven't blown. But there's a
Very loud hum and the light limiter is bright.
Voltage to tda's way down at 5v. Not fans. Front of board
Is unresponsive. No sound from the fx.
But unplug the tda's voltages seem to return to normal.
Fx, fans and front of board work. But limiter light still glowing not
As bright but still glowing. I also checked the speaker wasn't shorted.
Anyone had this problem.
Very loud hum and the light limiter is bright.
Voltage to tda's way down at 5v. Not fans. Front of board
Is unresponsive. No sound from the fx.
But unplug the tda's voltages seem to return to normal.
Fx, fans and front of board work. But limiter light still glowing not
As bright but still glowing. I also checked the speaker wasn't shorted.
Anyone had this problem.
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