hi
i own an nice receiver heco 2000(german version of leak 2000).it worked fine but had a loud hum noise(around 120hz).so i've replaced the 2 power supply capacitors.2 decent samwha 10000uf 63v(the original 6800uf 40v).the hum noise there is still but now is very slight.more audible whit low impedence headphones and through speakers(more hum noise from right speaker.
the dc offset is:right: 55mV , left: 75 mV.a little high?
I've set the bias on other amps(whit very clear istructions on service manual), but the process for this heco/leak 2000 is not clear to me as my electronic skills are a bit basic. Can anyone spell out exactly where i should be placing my digital multimeter black-red probes?i've seen where is it the potentiometer vr1(on main amplifier pcb.2 vr1..i presume one for left channel and one for right channel). I've attached the instructions from the service manual.photo of part of service which explains how to adjust quiescent current and 2 photos of electrical diagram.i hope the pages are clear
i own an nice receiver heco 2000(german version of leak 2000).it worked fine but had a loud hum noise(around 120hz).so i've replaced the 2 power supply capacitors.2 decent samwha 10000uf 63v(the original 6800uf 40v).the hum noise there is still but now is very slight.more audible whit low impedence headphones and through speakers(more hum noise from right speaker.
the dc offset is:right: 55mV , left: 75 mV.a little high?
I've set the bias on other amps(whit very clear istructions on service manual), but the process for this heco/leak 2000 is not clear to me as my electronic skills are a bit basic. Can anyone spell out exactly where i should be placing my digital multimeter black-red probes?i've seen where is it the potentiometer vr1(on main amplifier pcb.2 vr1..i presume one for left channel and one for right channel). I've attached the instructions from the service manual.photo of part of service which explains how to adjust quiescent current and 2 photos of electrical diagram.i hope the pages are clear
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Measure it across the emitter resistor of TR21, adjusting mA to mV according to Ohm’s Law. Not shown on this schematic, but must be somewhere.
hi ejp.
this service manual is very complicated.
the emitter resistor of TR21 where it is located in the diagram?
this service manual is very complicated.
the emitter resistor of TR21 where it is located in the diagram?
Measure across R36 and R37 (0R33). Measure across both without any load connected, if they gave you the value for one, double it across two.
Your DC offsets are too high. TR6 and TR7 should be closely matched, they are not. C7 (47uF) should be checked, if leaky will make the DC offset worse. This does affect sound quality and it may be going open by now. Make sure TR6 and TR7 are physically together, heat shrink if you can.
Your DC offsets are too high. TR6 and TR7 should be closely matched, they are not. C7 (47uF) should be checked, if leaky will make the DC offset worse. This does affect sound quality and it may be going open by now. Make sure TR6 and TR7 are physically together, heat shrink if you can.
hi anatech.
ok.bias set across r36 and r37.left channel adjusted at 90mV.but right channel doesn't have an easy adjustment.when i turn vr1(a little over half) the 2 fuse blow up.
the differential transistor is tr6-tr7 or tr7-tr8 ??
ok.bias set across r36 and r37.left channel adjusted at 90mV.but right channel doesn't have an easy adjustment.when i turn vr1(a little over half) the 2 fuse blow up.
the differential transistor is tr6-tr7 or tr7-tr8 ??
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Hi,
Okay, they want 90 mA (which is pretty high), that would be 59.4 mV across the two resistors, or just under 30 mV across one resistor. That's the one channel for R36 and R37, you would use a different pair of resistors for the other channel. Whatever 0R33 R resistors there are between the output emitter terminals.
The differential is TR7 and TR8 for one channel. I can't see the other channel schematic so I haven't a clue as to what part numbers there are for the other channel. If they use the same board, then the part location codes should be the same.
My opinion is that 90 mA for bias current is stupid high. Most amplifiers run between 20 and 30 mA and you don't even need that much. Cut it in half - ish and set for 40 mA would be my advice.
The channel blowing fuses. If you are measuring in the right place, you need an oscilloscope for this, but check to see if it isn't oscillating. If you are measuring the right points, I'll bet it is oscillating. There can be other faults, but those are more rare. If you don't have a 'scope or can't borrow one, refer this to a qualified electronic AUDIO technician.
Okay, they want 90 mA (which is pretty high), that would be 59.4 mV across the two resistors, or just under 30 mV across one resistor. That's the one channel for R36 and R37, you would use a different pair of resistors for the other channel. Whatever 0R33 R resistors there are between the output emitter terminals.
The differential is TR7 and TR8 for one channel. I can't see the other channel schematic so I haven't a clue as to what part numbers there are for the other channel. If they use the same board, then the part location codes should be the same.
My opinion is that 90 mA for bias current is stupid high. Most amplifiers run between 20 and 30 mA and you don't even need that much. Cut it in half - ish and set for 40 mA would be my advice.
The channel blowing fuses. If you are measuring in the right place, you need an oscilloscope for this, but check to see if it isn't oscillating. If you are measuring the right points, I'll bet it is oscillating. There can be other faults, but those are more rare. If you don't have a 'scope or can't borrow one, refer this to a qualified electronic AUDIO technician.