Hi!
I have an 8302 with high DC voltage at the speaker outputs. The outputs are fine. Disconnecting a couple of other components allowed me to trace voltage to some SMD components.
One side shows a short between B and E on Q310.
On the other side, the capacitors get hot.
So I have two needs.
1) What point should I be using as the ground reference to measure voltages.
2) Does anyone have a schematic?
Thanks!
I have an 8302 with high DC voltage at the speaker outputs. The outputs are fine. Disconnecting a couple of other components allowed me to trace voltage to some SMD components.
One side shows a short between B and E on Q310.
On the other side, the capacitors get hot.
So I have two needs.
1) What point should I be using as the ground reference to measure voltages.
2) Does anyone have a schematic?
Thanks!
That transistor (and a 150 ohm resistor in series with its base) is across the 0.22 ohm resistors. If it's shorted, confirm that the emitter resistors are within tolerance and haven't opened.
There is no isolation between the secondary ground and chassis ground. The most convenient reference points are the chassis ground terminal or the non-bridging speaker terminals.
Which capacitors are getting hot?
There is no isolation between the secondary ground and chassis ground. The most convenient reference points are the chassis ground terminal or the non-bridging speaker terminals.
Which capacitors are getting hot?
C216 gets especially hot. Probably because it's marked 10V and there is -22V there. Though even with one leg disconnected it gets hot? Is that right? I think it is.
Other one is same value, but no PCB marking that I can find.
Emitter (Source) resistors for the outputs? One pair it's on Source, other pair is Drain. I assume these are RL.
These amps are a foreign design to me.
Other one is same value, but no PCB marking that I can find.
Emitter (Source) resistors for the outputs? One pair it's on Source, other pair is Drain. I assume these are RL.
These amps are a foreign design to me.
The two 430 ohm resistors are probably producing the heat. They are connected across the output of the amp. If you have DC, they will get hot.
Yes, the 0.22 ohm resistors are on the source of the high-side FETs and on the drain of the low side FETs.
Is the DC on the output positive or negative?
Yes, the 0.22 ohm resistors are on the source of the high-side FETs and on the drain of the low side FETs.
Is the DC on the output positive or negative?
I believe you are right that the 430ohm resistors are heating the PCB which is heating the board, transferring to the caps.
R- 20.9V
L+ -6.3V
R- 20.9V
L+ -6.3V
Do you have both positive AND negative voltage on the op-amp power supply pins in the amp.
Check ALL of the op-amps (TL074s and NE5532s). Some are isolated by 10 ohm resistors so there's no guarantee that you'll have supply voltage on all op-amps just because you have it on one op-amp.
Check ALL of the op-amps (TL074s and NE5532s). Some are isolated by 10 ohm resistors so there's no guarantee that you'll have supply voltage on all op-amps just because you have it on one op-amp.
With respect to ground:
TL494C
4 = .837
7 = .3
12 = 12.2 (input voltage)
16 = .4 (should this be 5V?)
LM339M
3 = 12.2
12 = 0.3
TL074C (both)
4 = -19.79
11 = -21.43
NE5532
4 = -21.43
8 = -19.82
TL494C
4 = .837
7 = .3
12 = 12.2 (input voltage)
16 = .4 (should this be 5V?)
LM339M
3 = 12.2
12 = 0.3
TL074C (both)
4 = -19.79
11 = -21.43
NE5532
4 = -21.43
8 = -19.82
With respect to ground:
TL494C
4 = .837
7 = .3
12 = 12.2 (input voltage)
16 = .4 (should this be 5V?) >>>> No.
LM339M
3 = 12.2
12 = 0.3
TL074C (both)
4 = -19.79 >>>> Isn't this positive?
11 = -21.43
NE5532
4 = -21.43
8 = -19.82 >>>> Isn't this positive?
TL494C
4 = .837
7 = .3
12 = 12.2 (input voltage)
16 = .4 (should this be 5V?) >>>> No.
LM339M
3 = 12.2
12 = 0.3
TL074C (both)
4 = -19.79 >>>> Isn't this positive?
11 = -21.43
NE5532
4 = -21.43
8 = -19.82 >>>> Isn't this positive?
Probably an open positive 18v regulator. What is the voltage on the 3 terminals of the A06 (PZTA06) transistor near D90?
B (1) = 32.1
C (2) = 32.9
E (3) = -19.7
The second one I have had this very same device replaced by someone else but still exhibits the same problem. A trend possibly?
C (2) = 32.9
E (3) = -19.7
The second one I have had this very same device replaced by someone else but still exhibits the same problem. A trend possibly?
You should have approximately...
B: 19v
C: 32v
E: 18v
The zener connected to the base is either open or has bad connections.
The transistor is open or has bad connections.
The filter capacitor connected to the emitter of the transistor has probably been damaged by the reverse voltage.
MTX amplifiers have a lot of problems with the regulators. After you get it working, you may want to swap out the PZTA06s for larger transistors with heatsinks. I've done this on quite a few amps and have never had one return with failed regulators.
http://www.bcae1.com/temp/IMG_6215b.jpg
B: 19v
C: 32v
E: 18v
The zener connected to the base is either open or has bad connections.
The transistor is open or has bad connections.
The filter capacitor connected to the emitter of the transistor has probably been damaged by the reverse voltage.
MTX amplifiers have a lot of problems with the regulators. After you get it working, you may want to swap out the PZTA06s for larger transistors with heatsinks. I've done this on quite a few amps and have never had one return with failed regulators.
http://www.bcae1.com/temp/IMG_6215b.jpg
The board is so spread out with traces everywhere, it's hard to follow.
D90 appears to be good. I don't find any other diodes. Is there an ID?
C92 appears to be good. Removed it and still had -19V? Was there another possible source?
The transistor definitely tested bad once removed. Base open, C&E leaky.
D90 appears to be good. I don't find any other diodes. Is there an ID?
C92 appears to be good. Removed it and still had -19V? Was there another possible source?
The transistor definitely tested bad once removed. Base open, C&E leaky.
I don't understand the question.
You still have -19v because the -18v regulator is working. The voltage is being transferred through the op-amps.
Lifting the emitter gives full rail voltage. I assume because the Base is turned all the way on. However, I leaned on it a little bit with it connected and voltage drops to -4V pretty easily. Probably would go further with full power.
D91 is connected, but has high resistance (Mohms) in both directions. Diode test says 1.2V one way and 1.0V the other.
I cannot figure out how to determine the value for D91. SMD codebook lists two zeners for J3, I assume it's supposed to be 18V?
D91 is connected, but has high resistance (Mohms) in both directions. Diode test says 1.2V one way and 1.0V the other.
I cannot figure out how to determine the value for D91. SMD codebook lists two zeners for J3, I assume it's supposed to be 18V?
Replaced D91. Seems to work fine with emitter disconnected.
Once I connect the emitter, the voltage starts going negative around 8.8V input and at 9V input, the PS load is 2A.
Once I connect the emitter, the voltage starts going negative around 8.8V input and at 9V input, the PS load is 2A.
You may have a shorted/damaged op-amp.
"Once I connect the emitter, the voltage starts going negative"
Do you mean that the voltage on the emitter goes below 0v DC or doi you mean it begins to fall from 18v?
"around 8.8V input and at 9V input, the PS load is 2A."
Are you referring to the B+ power supply voltage?
Are any of the op-amps getting hot?
"Once I connect the emitter, the voltage starts going negative"
Do you mean that the voltage on the emitter goes below 0v DC or doi you mean it begins to fall from 18v?
"around 8.8V input and at 9V input, the PS load is 2A."
Are you referring to the B+ power supply voltage?
Are any of the op-amps getting hot?
Yes, the voltage is below 0V.
I don't find any hot op amps. Either by touch or by thermocouple.
Fets 601 and 602 are getting warm, but not 603 and 604.
I don't find any hot op amps. Either by touch or by thermocouple.
Fets 601 and 602 are getting warm, but not 603 and 604.
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