On the schematic there is a number under "S1" that's the temp. of the switch in Celsius (105C in this case) and I'm looking at my 400RB III which has the same protection circuit.
Craig
Craig
Tauro02211,
Which schematic are you using, 150 or 400? We're talking about a 400 at the moment aren't we? If the amp is working normally the signals/voltages to Q2 (+ to the base and - to the emitter) would be balanced. Any "major" unbalance would trip the protection circuit, Q2-Q11-Q12-U1, a closed S1 keeps Q10 out of the loop unless there is a temperature problem. If R3 (fuse) is open we're starting out with an unbalance at turn on.
Craig
Which schematic are you using, 150 or 400? We're talking about a 400 at the moment aren't we? If the amp is working normally the signals/voltages to Q2 (+ to the base and - to the emitter) would be balanced. Any "major" unbalance would trip the protection circuit, Q2-Q11-Q12-U1, a closed S1 keeps Q10 out of the loop unless there is a temperature problem. If R3 (fuse) is open we're starting out with an unbalance at turn on.
Craig
Post #9 has the 400 schematic. All of the circuitry is pretty much the same but with different part designations. It was a 150 at the beginning.
Craig
Craig
Hi,
Can you check the voltage AT PIN 3 OF THE 555. Should be zero and the D11 should be 7.5 volts.
Can you check the voltage AT PIN 3 OF THE 555. Should be zero and the D11 should be 7.5 volts.
Hi frickecello,
Maybe I should have explain 555 circuit more clearly.It does not
shut down power at all as the output of 555 ic only lights up the red led (protection)🙂 so it only indicate a fault condition sensed from the "fault" input plus the turn on delay of 4 seconds.
Now. you have given another clue (power cutoff).What could have
caused this? Well you have replaced all output transistors so it's not the output. S1 is only a momentary on/off switch and not a temperature switch
triggering at 105 celcius degree.If you look at your schematic there is a fan
circuit and there is a temperature switch Q27 ,a LM35.
Remove the fan connector and check for shorts ,of course not forgetting the
fan coil as it takes +60V for power. If the fault is not here,go back to output,bias circuit to check again ,you may have missed something.
PS S1 may be the fan circuit? Conventional circuit drawing does not indicate as such.Hmmmm....
Singa
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The problem is that you are experiencing a power cut off. If you have a shorted in some place you will blow the main fuse and your are not. Can you check the voltage at the R63/R64 . These are current limiter resistor at powered. In the above thread you said that the 555 is only an indication and not a shut down circuit. We need to look what may caused a power cutoff with no damage visible.
Can you check the voltage at the rectifier BR1. You should see voltage all the time after powered since there is not shutdown.
If you check voltage at BR1 you should see -60 volts and +60 volts and should not cutoff after powered the amplifier.
Hi frickecello,
Assuming S1 is a temperature switch which normally connect
supply to bias transistors.If say it opens and power is cut off then where could the massive short come from,you said power rails are OK so that rules out the power supply including the diode bridge and power caps.The heat sinks will heat up and that's a telltale sign.Does the heatsink get hot?
So the only other option is the fan circuit which also use +60V.😱
Or some other thing?
PS do what tauro02211 says about the resistors check them.
Lm35 is not a switch but a sensor ,sorry.
Singa
Assuming S1 is a temperature switch which normally connect
supply to bias transistors.If say it opens and power is cut off then where could the massive short come from,you said power rails are OK so that rules out the power supply including the diode bridge and power caps.The heat sinks will heat up and that's a telltale sign.Does the heatsink get hot?
So the only other option is the fan circuit which also use +60V.😱
Or some other thing?
PS do what tauro02211 says about the resistors check them.
Lm35 is not a switch but a sensor ,sorry.
Singa
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I studied the 400 amplifier circuit and found that the mute signal coming from the 555 will disable the Q4/Q3 that will removed the ground to the differential amplifier composed of Q7A/Q7B. This will removed the voltage to the drivers for the output transistors. Indirectly the 555 is shutting down the amplifier. It is too late I will follow it tomorrow. Good luck
"Hasta la vista"
"Hasta la vista"
I forget that the 150 the 555 mute coming from the 555 will also shutdown the outputs. Same circuit
Hi guys,
First of all thanks for all your replies, you've been very helpful!
Now I'm pretty sure that the mute circuit turns off the entire power amp section as tauro0221 stated and I thought it did. And I confirmed that the protection circuit works fine.
I checked important components in the amp again, and this is what I found:
R3 is below tolerance (measured 850 ohms what do you think?)
R45 is open (doesn't look burned though, checked all fuse resistors as well)
R19 is OK (bias pot)
Q16 is CE shorted (measured 10 ohms)
Q8 appears to be CE shorted as well (measured 180 ohms)
Q18 is CE shorted
Q24, Q25 and Q26 are CE shorted.
I'm not sure if I should replace Q14, Q21, Q22 and Q23 since they fail the diode test, but not the continuity test (not CE shorted), how can I be sure these are bad or not?
First of all thanks for all your replies, you've been very helpful!
Now I'm pretty sure that the mute circuit turns off the entire power amp section as tauro0221 stated and I thought it did. And I confirmed that the protection circuit works fine.
I checked important components in the amp again, and this is what I found:
R3 is below tolerance (measured 850 ohms what do you think?)
R45 is open (doesn't look burned though, checked all fuse resistors as well)
R19 is OK (bias pot)
Q16 is CE shorted (measured 10 ohms)
Q8 appears to be CE shorted as well (measured 180 ohms)
Q18 is CE shorted
Q24, Q25 and Q26 are CE shorted.
I'm not sure if I should replace Q14, Q21, Q22 and Q23 since they fail the diode test, but not the continuity test (not CE shorted), how can I be sure these are bad or not?
Hi frikecello,
Now you are getting somewhere,the trick is not to confuse yourself by assuming too much and jumping all over the circuit.You have to understand how each section of the circuit works.So you have determined the 555 circuit is OK and therefore the fault is somewhere else which most technicians will zero in the output because it is high power ,most likely to fail.
1. R3 measured in circuit is 850 ohm compared to stated value
of 1K ohm.Normally it is lower when measured in circuit so I assume it is OK.
But do check it out of the circuit.
2. R45 68.1 ohm between channels of both driver and output transistors.A telltale sign that a major fault happened in this stage because it is sitting between both power rails of +/- 60V.Lots of current can pass through either way if there is a fault.
3. Q16 one of the bias transistor shorted.Now you can suspect a component to be shorted when the value lies between 0 - 30 ohm.So the only way to confirm is to desolder them out to check.I will agree with you on Q16.
Q8 at 180 ohm but look at R22, 182 ohm.This isin circuit 4. so may be
not be the real resistance of Q8.Or is Q8 open?Check with correct polarity of meter probe from B-E and B-C,if both conduct and the reverse happen when the polarity of B is switch then in most cases the transistor is functional.
4. Q18 driver, Q24.25,26 output transistors CE shorted.Please remember this is in circuit and there are 0.1 ohm resistors around both sides. But Q14,21,22,23 are not CE shorted.This could meant that only one complete channel is shorted.So the only way to confirm is to desolder them one at a time and measure out of the circuit.
5. Check stage by stage i.e. if you want to start at the bias then proceed step by step to confirm or you may confuse yourself.
6. I think you can safely power up without the output transistors installed
so that you can check th voltages of the input section including the mute
circuit(after you have replaced the bad components).Don't forget to check power supply for +/-35V and +/-15V.
See the first time you replaced all the outputs only to fail again without
checking the rest of the associated components which is a costly mistake.
So check thoroughly this time and you will get your amp back in working
condition soon.🙂
Ps I don't think the mute circuit turns off the power amp,how can it turn off when it is supposed to shut down the input Q7A,B thus cutting off the signal
to the driver Q14,18.Remember it is muting not cutoff the power or output section.It appears that way because R45 is open and the outputs are shorted.
Singa.
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Hi guys,
Parts arrived from Mouser and after desoldering components that supposed to be damaged, only R45 and Q24 needed to be replaced (Q24 was CB and CE shorted).
After replacing components I turned the amp on without load, and the same happens, the protection circuit keeps being triggered.
I checked drivers and power transistors for CE shorts and they are OK.
After turning the amp on I checked R45 (which I previously replaced) and it wasn't damaged. Checked all fuse resistors as well and they are OK.
Checked +/- 60, +/- 35 (measured +/-45) and +/- 15 power rails and they are OK.
What do you guys think?
Parts arrived from Mouser and after desoldering components that supposed to be damaged, only R45 and Q24 needed to be replaced (Q24 was CB and CE shorted).
After replacing components I turned the amp on without load, and the same happens, the protection circuit keeps being triggered.
I checked drivers and power transistors for CE shorts and they are OK.
After turning the amp on I checked R45 (which I previously replaced) and it wasn't damaged. Checked all fuse resistors as well and they are OK.
Checked +/- 60, +/- 35 (measured +/-45) and +/- 15 power rails and they are OK.
What do you guys think?
Hi,
Let me correct my self when I mean power down. What I mean is that will removed the driver voltage for the output transistors.
One check you can do is the base/collector voltage of Q11. This is were the protect is trigger by enable Q10. This is in the circuit tied to Q24/Q19/Q23/Q20/Q19.
Let me correct my self when I mean power down. What I mean is that will removed the driver voltage for the output transistors.
One check you can do is the base/collector voltage of Q11. This is were the protect is trigger by enable Q10. This is in the circuit tied to Q24/Q19/Q23/Q20/Q19.
Hi frickecello,
Here we go again😱 So R45 and Q24 was bad and this is the
output section but how is it triggered since you have now replaced them
and they should be functional? ( protection circuit).
1. Logically I would investigate Q11 and zener D7 5.1V so you should
get a reading of around 5V when powered.
2. From Q24 it goes to R3,R1,D1,Q2,C2 and R2. Check D1 schottky diode
you should get a low ohm reading but it does not mean it is short unless it
is almost zero.
3. I would also check bias circuit Q8,Q16 and surrounding components.
4. Check also D1 and Q2 which is part of bias circuit.D1 is schottky too
so expect a low ohm reading unless short or open.
5. Also check D4 and D6 and the input section.
Once again good hunting.🙂 singa
Here we go again😱 So R45 and Q24 was bad and this is the
output section but how is it triggered since you have now replaced them
and they should be functional? ( protection circuit).
1. Logically I would investigate Q11 and zener D7 5.1V so you should
get a reading of around 5V when powered.
2. From Q24 it goes to R3,R1,D1,Q2,C2 and R2. Check D1 schottky diode
you should get a low ohm reading but it does not mean it is short unless it
is almost zero.
3. I would also check bias circuit Q8,Q16 and surrounding components.
4. Check also D1 and Q2 which is part of bias circuit.D1 is schottky too
so expect a low ohm reading unless short or open.
5. Also check D4 and D6 and the input section.
Once again good hunting.🙂 singa
Hi tauro0221 and singa,
I checked all components, and only D1 seems to be damaged since it did not measure a low ohm value, I got two different resistance values with different multimeters, around 800 ohms and 3k ohms, but never less than 100 ohms.
What do you think?
I checked all components, and only D1 seems to be damaged since it did not measure a low ohm value, I got two different resistance values with different multimeters, around 800 ohms and 3k ohms, but never less than 100 ohms.
What do you think?
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