1. When the HK930 is connected via the "tape out" jacks to the aux input jacks of another receiver and with FM selected on the HK930, the tuner of this HK930 will drive the other receiver and it sounds fine.
2. When the HK930 is connected via the "preamp out" jacks to the "power amp in" jacks of the other receiver and with FM selected on the HK930, the preamp of the HK930 fails to drive the power amp of the other receiver above a very low volume and one channel is even lower in volume than the other. This same behavior is exists when the HK930 preamp drives its own amp.
3. When the other receiver is connected via the preamp out jacks to the "main amp in" jacks of the HK930 and the tuner is selected on the other receiver, the main amp of the HK930 is successfully driven by the other receiver.
Probable cause:
Each channel on this unit has its own separate power supply. Everything was working fine until I accidentally soldered together the two B+ lines of the two separate power supplies.
Here is a link to the tech manual for this unit:
http://manuals.harman.com/HK/Service Manual/HK930 sm.pdf
It is minimal but it has the schematics. The phono stage is referred to as the preamp. The preamp is referred to as the "tone control board". The main amp is referred to as the predriver.
I replaced all the electrolytic caps on this unit and the input differential pairs of transistors in the main amp section. After this, I attempted to switch the power supplies in an effort to isolate another minor problem that could have arisen from the power supply, the preamp or the main amp. That's when I accidentally soldered the two B+ lines together. A very very thin filament of soldered bridged the very narrow space between the two soldering posts.
I checked all the transistors and electrolytic caps in the preamp for shorts and found none. The schematics do not have any voltages on them except those of the B+ and B- lines and they check out okay.
Does anyone have any hints or suggestions on how I might isolate this problem? Each channel in the preamp has a pair of 2SC644's at the input stage and a 2SC644 and a 2SC828 at the output stage with the 2SC828 being the output transistor. The voltage to the preamp is 19.5 volts, exactly half of the voltage between B+ and ground. The section of the power supply that powers the preamp also powers the FM tuner and the FM tuner appears to be working okay so I am going on the assumption that the voltage to the preamp is correct.
I don't know exactly what to infer from the fact that I am getting at least some output from each channel of the preamp output, with one channel being weaker than the other. My guess is that even though none of the transistors are shorted across any of the three leads in any direction, the problem lies with the transistors. I am considering borrowing the 2SC644 transistors from the phono stage to use in the preamp. I guess my question would be which end of the preamp would the faulty transistors most likely be located, at the input of the output?
Thanks,
Jack
2. When the HK930 is connected via the "preamp out" jacks to the "power amp in" jacks of the other receiver and with FM selected on the HK930, the preamp of the HK930 fails to drive the power amp of the other receiver above a very low volume and one channel is even lower in volume than the other. This same behavior is exists when the HK930 preamp drives its own amp.
3. When the other receiver is connected via the preamp out jacks to the "main amp in" jacks of the HK930 and the tuner is selected on the other receiver, the main amp of the HK930 is successfully driven by the other receiver.
Probable cause:
Each channel on this unit has its own separate power supply. Everything was working fine until I accidentally soldered together the two B+ lines of the two separate power supplies.
Here is a link to the tech manual for this unit:
http://manuals.harman.com/HK/Service Manual/HK930 sm.pdf
It is minimal but it has the schematics. The phono stage is referred to as the preamp. The preamp is referred to as the "tone control board". The main amp is referred to as the predriver.
I replaced all the electrolytic caps on this unit and the input differential pairs of transistors in the main amp section. After this, I attempted to switch the power supplies in an effort to isolate another minor problem that could have arisen from the power supply, the preamp or the main amp. That's when I accidentally soldered the two B+ lines together. A very very thin filament of soldered bridged the very narrow space between the two soldering posts.
I checked all the transistors and electrolytic caps in the preamp for shorts and found none. The schematics do not have any voltages on them except those of the B+ and B- lines and they check out okay.
Does anyone have any hints or suggestions on how I might isolate this problem? Each channel in the preamp has a pair of 2SC644's at the input stage and a 2SC644 and a 2SC828 at the output stage with the 2SC828 being the output transistor. The voltage to the preamp is 19.5 volts, exactly half of the voltage between B+ and ground. The section of the power supply that powers the preamp also powers the FM tuner and the FM tuner appears to be working okay so I am going on the assumption that the voltage to the preamp is correct.
I don't know exactly what to infer from the fact that I am getting at least some output from each channel of the preamp output, with one channel being weaker than the other. My guess is that even though none of the transistors are shorted across any of the three leads in any direction, the problem lies with the transistors. I am considering borrowing the 2SC644 transistors from the phono stage to use in the preamp. I guess my question would be which end of the preamp would the faulty transistors most likely be located, at the input of the output?
Thanks,
Jack
