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Kevin's Hafler p-500
- Thread starter kevin
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- Jan 14, 2011
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- Gillette, Wyo.
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- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,912
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,912
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,912
- Location
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- Tagline
- Halfbiass...Electron Herder and Backass Woof
This Hafler is Kickin' My Tail
To All,
Need some help with the Hafler P500 in question, I think it helps to write it all down but even better when you have someone who can help you think, here are the conditions:
The left channel works fine. The right channel has no output unless the volume is turned up to the maximum and then the clip light comes on and the output sound is extremely broken distortion, not resembling a 2KHz test signal at all. The DC offsets are left (normal) .003VDC, right is .140VDC. On the scope, the right channel shows no AC waveform. Test point "C" appears normal, a half sine wave in synch with the input signal. Test point "D" is a flat line. The owners states there was no physical activity taking place when the right channel failed and the output was not at maximum levels.
The preamp board has normal outputs on both channels and the speaker output relay functions normally, so the problem is confined to the PC-19C amplifier board. The board is receiving the correct input signal and both B+ and B- rail voltages (90.0VDC) are present. The B+ and B- rail supply 10 Amp fuses have never blown, neither has the 5 Amp speaker protect fuse. The outputs are not grounded, all six of the right channel output MOSFETs check out good with no shorts or opens; one N-channel device was questionable and it has been replaced. I also replaced the original 100mfd/100V electrolytic capacitors C12 and C14, along with the NP 220mfd/10V electrolytic capacitor C8 with Nichicon Muse components.
Referring to the PC-19C amplifier board:
The input differential pair seem to be working properly (they were replaced by new 2N5550/2N5401 transistors), except the output of Q5 is bad (no sine wave) this may be due to a downstream condition or maybe the transistor is not turned on? The DC voltages on the input pair are:
Positive side:
Q3 NPN (2N5550) - E: 1.25V, B: -0.7V, C: 87V
Negative side:
Q5 PNP (2N5401) - E: 0.375V, B: 0.7V, C: -87V
These should be the same, but would this minor difference on the negative side cause zero output?
Emitter bias may be a bit low on Q5, so the transistors that supply the front end bias Q1 and Q2 were also replaced with no change. The DC voltages properly correspond to the voltages on the opposite side differential input devices and on this pair are:
Positive side:
Q1 PNP (2N5401) - E: 86.3V, B: 85.2V, C: -0.38V
Negative side:
Q2 NPN (2N5550) - E: -84V, B: -85V, C: -1.26V
For the lower voltage, I suspect the diode train D1, D2, and D3 on the base of Q1 although they test good in circuit. I should just replace all three 1N4148s, I have plenty.
For comparison, the transistors that are not in the signal path but supply the feedback to the front end Q4 and Q6 were also replaced just to make sure. The DC voltages on this pair are:
Positive side:
Q4 NPN (2N5550) - E: -1.1V, B: -0.55V, C: 82.7V
Negative side:
Q6 PNP (2N5401) - E: 0.59V, B: 0.55V, C: -86.3V
Seems normal for this application with 0V on the output.
Beyond the differential input pair, the current amplifier configuration of Q7 and Q8 on the positive side and Q10 and Q11 on the negative side had predictable results based on what they received from the input pair transistors. Q7 had a good input (same as the output of Q3) with an output that looked distorted as if it was being pulled down by the next device Q8. I replaced Q7 with no effect and then I looked at Q8. I compared the DC voltages with the other side and decided to replace it because I had some 2N5415 transistors, no change. The DC voltages on this pair are:
Positive side:
Q7 PNP (2N5401) - E: 88V, B: 88V, C: 0V
Q8 PNP (2N5415) - E: 88V, B: 88V, C: .02V
Negative side:
Q10 NPN (2N5550) - E: -87V, B: -87V, C: 0V
Q11 NPN (2N3440) - E: -87V, B: -87V, C: 0V
The base of Q7 is high because the collector of Q3 is also high, is this normal? The bias resistors for Q3 and Q7 are 1800 Ohms, so I guess it's correct. The collectors of both Q7 and Q10 devices are held to signal ground, so those voltages are valid.
The pre-drivers Q12 and Q13 also have similar voltage readings to each other and I replaced Q12 2N3440 with a more robust 2N3439 with no change. The DC voltages on this pair are:
Positive side:
Q12 NPN (2N3439) - E: 0.2V, B: .02V, C: 89V
Negative side:
Q13 PNP (2N5415) - E: .02V, B: .02V, C: -88V
The low output on the emitters of these devices accounts for the MOSFETs on the Right channel staying cool while the outputs on the Left channel get warm.
Have I given enough information to see a solution? It seems the problem may be in the current amplifier bias supply. From there I am lost as I cannot remember enough transistor theory to know if the transistors are biased properly or not. I have eliminated many of the before and after components but I have to find the problem on this board because I know of at least one other board that has the same symptoms. Short of buying a parts amp and replacing the whole board, I have easter-egged enough and I need to understand the failure mode.
Thanks,
Mark
To All,
Need some help with the Hafler P500 in question, I think it helps to write it all down but even better when you have someone who can help you think, here are the conditions:
The left channel works fine. The right channel has no output unless the volume is turned up to the maximum and then the clip light comes on and the output sound is extremely broken distortion, not resembling a 2KHz test signal at all. The DC offsets are left (normal) .003VDC, right is .140VDC. On the scope, the right channel shows no AC waveform. Test point "C" appears normal, a half sine wave in synch with the input signal. Test point "D" is a flat line. The owners states there was no physical activity taking place when the right channel failed and the output was not at maximum levels.
The preamp board has normal outputs on both channels and the speaker output relay functions normally, so the problem is confined to the PC-19C amplifier board. The board is receiving the correct input signal and both B+ and B- rail voltages (90.0VDC) are present. The B+ and B- rail supply 10 Amp fuses have never blown, neither has the 5 Amp speaker protect fuse. The outputs are not grounded, all six of the right channel output MOSFETs check out good with no shorts or opens; one N-channel device was questionable and it has been replaced. I also replaced the original 100mfd/100V electrolytic capacitors C12 and C14, along with the NP 220mfd/10V electrolytic capacitor C8 with Nichicon Muse components.
Referring to the PC-19C amplifier board:
The input differential pair seem to be working properly (they were replaced by new 2N5550/2N5401 transistors), except the output of Q5 is bad (no sine wave) this may be due to a downstream condition or maybe the transistor is not turned on? The DC voltages on the input pair are:
Positive side:
Q3 NPN (2N5550) - E: 1.25V, B: -0.7V, C: 87V
Negative side:
Q5 PNP (2N5401) - E: 0.375V, B: 0.7V, C: -87V
These should be the same, but would this minor difference on the negative side cause zero output?
Emitter bias may be a bit low on Q5, so the transistors that supply the front end bias Q1 and Q2 were also replaced with no change. The DC voltages properly correspond to the voltages on the opposite side differential input devices and on this pair are:
Positive side:
Q1 PNP (2N5401) - E: 86.3V, B: 85.2V, C: -0.38V
Negative side:
Q2 NPN (2N5550) - E: -84V, B: -85V, C: -1.26V
For the lower voltage, I suspect the diode train D1, D2, and D3 on the base of Q1 although they test good in circuit. I should just replace all three 1N4148s, I have plenty.
For comparison, the transistors that are not in the signal path but supply the feedback to the front end Q4 and Q6 were also replaced just to make sure. The DC voltages on this pair are:
Positive side:
Q4 NPN (2N5550) - E: -1.1V, B: -0.55V, C: 82.7V
Negative side:
Q6 PNP (2N5401) - E: 0.59V, B: 0.55V, C: -86.3V
Seems normal for this application with 0V on the output.
Beyond the differential input pair, the current amplifier configuration of Q7 and Q8 on the positive side and Q10 and Q11 on the negative side had predictable results based on what they received from the input pair transistors. Q7 had a good input (same as the output of Q3) with an output that looked distorted as if it was being pulled down by the next device Q8. I replaced Q7 with no effect and then I looked at Q8. I compared the DC voltages with the other side and decided to replace it because I had some 2N5415 transistors, no change. The DC voltages on this pair are:
Positive side:
Q7 PNP (2N5401) - E: 88V, B: 88V, C: 0V
Q8 PNP (2N5415) - E: 88V, B: 88V, C: .02V
Negative side:
Q10 NPN (2N5550) - E: -87V, B: -87V, C: 0V
Q11 NPN (2N3440) - E: -87V, B: -87V, C: 0V
The base of Q7 is high because the collector of Q3 is also high, is this normal? The bias resistors for Q3 and Q7 are 1800 Ohms, so I guess it's correct. The collectors of both Q7 and Q10 devices are held to signal ground, so those voltages are valid.
The pre-drivers Q12 and Q13 also have similar voltage readings to each other and I replaced Q12 2N3440 with a more robust 2N3439 with no change. The DC voltages on this pair are:
Positive side:
Q12 NPN (2N3439) - E: 0.2V, B: .02V, C: 89V
Negative side:
Q13 PNP (2N5415) - E: .02V, B: .02V, C: -88V
The low output on the emitters of these devices accounts for the MOSFETs on the Right channel staying cool while the outputs on the Left channel get warm.
Have I given enough information to see a solution? It seems the problem may be in the current amplifier bias supply. From there I am lost as I cannot remember enough transistor theory to know if the transistors are biased properly or not. I have eliminated many of the before and after components but I have to find the problem on this board because I know of at least one other board that has the same symptoms. Short of buying a parts amp and replacing the whole board, I have easter-egged enough and I need to understand the failure mode.
Thanks,
Mark
Last edited:
OMG..... I FEEL SO BAD THAT YOU ARE GOING THROUGH ALL THIS OVER THAT DAMN THING.... HELP LEE !!!!! HELP ! I wish I could send ya my other one but it does the exact same thing !!!! Mark .... You know that if you take that thing out in the driveway and run over it I DONT CARE !!! I know there is no way you will give up till ya fix it. I really do feel bad for getting ya into that ............
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)
- Joined
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- WassupYa Mang?
- Joined
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- Joined
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I know what ya mean, but I was referring to the virtual kind of sleep as in: this thing is causing me nightmares, I see Q7 in my sleep and it is leaking musical notes of The God Particle, it's awful. On a brighter note, thanks to you, I have every semiconductor used in the Hafler in my drawer of parts except for the one Q9 (NP2222A). I probably have a sub for it tho'.
Mark
Mark
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