Hello everybody.
i have a Sansui RZ-6500-avb home amplifier on my bench.
the outputs are isolated from each other, ie not a single compound IC, and seems to follow class AB style. the drivers are A940 and C2073 and main BJT's are B817 and D1047.
the amp came in with one channel worth of drivers and main bjts burnt, and was going into protect mode as soon as power was applied. i replaced the drivers and main bjts, and powered up the amp, it came on fine and played signal thru all other channels except the repaired one. the repaired channel just gave a hum at constant level irrespective of what volume was adjusted to.
preamps are in the form of riser cards and do supply the signal to the drivers, including the previously blown channel.
i tested semiconductors near the blown channel and located 2 zeners that where shorted. some investigation later i wrongfully identified that this was part of the audio clipper circuit. after removig these zeners, the channel does not pass any signal whatsoever.
i identified one as being a 1N4148, but im having trouble positively identifying the other. the 4148 zener has a black ring and the other diode has a white ring. i checked symetrical channels and the numbers "643" seem to be printed on the diode, i just cant be sure tho.
if anybody has had some experience working with this type of circuit and possibly knows what the diode could be, your help would be invaluable to me.
ideally, a schematic would be the holy grail for me right now.
many thanks in advance
i have a Sansui RZ-6500-avb home amplifier on my bench.
the outputs are isolated from each other, ie not a single compound IC, and seems to follow class AB style. the drivers are A940 and C2073 and main BJT's are B817 and D1047.
the amp came in with one channel worth of drivers and main bjts burnt, and was going into protect mode as soon as power was applied. i replaced the drivers and main bjts, and powered up the amp, it came on fine and played signal thru all other channels except the repaired one. the repaired channel just gave a hum at constant level irrespective of what volume was adjusted to.
preamps are in the form of riser cards and do supply the signal to the drivers, including the previously blown channel.
i tested semiconductors near the blown channel and located 2 zeners that where shorted. some investigation later i wrongfully identified that this was part of the audio clipper circuit. after removig these zeners, the channel does not pass any signal whatsoever.
i identified one as being a 1N4148, but im having trouble positively identifying the other. the 4148 zener has a black ring and the other diode has a white ring. i checked symetrical channels and the numbers "643" seem to be printed on the diode, i just cant be sure tho.
if anybody has had some experience working with this type of circuit and possibly knows what the diode could be, your help would be invaluable to me.
ideally, a schematic would be the holy grail for me right now.
many thanks in advance
The 1N4148 is not a Zener, but is a small signal diode.
https://www.vishay.com/docs/81857/1n4148.pdf
https://www.vishay.com/docs/81857/1n4148.pdf
Last edited:
> a schematic would be the holy grail
Sansui RZ-5200AV - Manual - Audio Video Receiver - HiFi Engine
Sansui RZ-5200AV - Manual - Audio Video Receiver - HiFi Engine
Hi PRR, i have had a look at a few variants of sanui manuals online, incluf=ding this one above and i havent been able to match to any part of my circuit.
im in the process of building a variable power supply, once complete, i will be able to test turn on voltage of a mirrored channel zener, which i will then replace both.
if anybody has this particular schematic, would be a huge help
im in the process of building a variable power supply, once complete, i will be able to test turn on voltage of a mirrored channel zener, which i will then replace both.
if anybody has this particular schematic, would be a huge help
What is "near"? Where are they on the PCBs?
You have two channels. One is working? Then voltage measurements compared one to the other should give Clues.
hello everybody
just an update on this amp, these diodes clip/clamp the audio signal being fed to the output transistors. one was a forward biased (1N4148) and the other was a reversed biased 5.6v zener.
the simplest way to check zener voltage is to look for conductance using a voltage and current regulated PSU.
these diodes where/are not critical to the channel producing output.
while replacing all seemingly dead components including the output balancing audio resistor, there is still some trouble with the channel in question.
i am officially fedup from stripping and refitting this amp into the chassis just so i may power up and probe different areas of the circuit, that i have put it aside for future frustration.
if any good people care to offer assistance, the audio signal from the driver card seems clean, and if memory serves me correctly, so too is the output audio from the unloaded output terminals. when that particular channel is loaded with a 4ohm high efficiency driver, the output sort of breaks down/drops out.
when scoping the loaded channel output and 10hz sine played into the input, the positive half of the sine wave looks to be satisfactory while the negative half sort of starts to build but then is pulled to ground.
audio thru the channel in question is distorted at best.
the channel loading doesnt affect the driver card output. i figured my problem lies between the output of the driver and the speaker terminals, and this is a relatively small area diagnose, but given the number of strips/fits....#fedup4now, but i will pick up this repair in future months to come
thanks for the help in advance
just an update on this amp, these diodes clip/clamp the audio signal being fed to the output transistors. one was a forward biased (1N4148) and the other was a reversed biased 5.6v zener.
the simplest way to check zener voltage is to look for conductance using a voltage and current regulated PSU.
these diodes where/are not critical to the channel producing output.
while replacing all seemingly dead components including the output balancing audio resistor, there is still some trouble with the channel in question.
i am officially fedup from stripping and refitting this amp into the chassis just so i may power up and probe different areas of the circuit, that i have put it aside for future frustration.
if any good people care to offer assistance, the audio signal from the driver card seems clean, and if memory serves me correctly, so too is the output audio from the unloaded output terminals. when that particular channel is loaded with a 4ohm high efficiency driver, the output sort of breaks down/drops out.
when scoping the loaded channel output and 10hz sine played into the input, the positive half of the sine wave looks to be satisfactory while the negative half sort of starts to build but then is pulled to ground.
audio thru the channel in question is distorted at best.
the channel loading doesnt affect the driver card output. i figured my problem lies between the output of the driver and the speaker terminals, and this is a relatively small area diagnose, but given the number of strips/fits....#fedup4now, but i will pick up this repair in future months to come
thanks for the help in advance
In case of output stage meltdown, there are a few components that often suffer and should be checked:
* output transistor emitter resistors
* resistors in series with output transistor base
* other misc. resistors in that area
* feedback network resistors
* capacitor in ground leg of feedback
* input transistor on the feedback side
The VAS transistor may also suffer. (Assuming a typical LTP - VAS - driver achitecture here. It being an '80s amp, it could be a LTP - LTP - driver thing, too.)
Since the output seems to collapse under load, the odd fried resistor seems likely.
You may want to bug a mod about moving this thread to Solid State.
* output transistor emitter resistors
* resistors in series with output transistor base
* other misc. resistors in that area
* feedback network resistors
* capacitor in ground leg of feedback
* input transistor on the feedback side
The VAS transistor may also suffer. (Assuming a typical LTP - VAS - driver achitecture here. It being an '80s amp, it could be a LTP - LTP - driver thing, too.)
Since the output seems to collapse under load, the odd fried resistor seems likely.
You may want to bug a mod about moving this thread to Solid State.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.