JoseHH
Well-Known Member
Hello everyone.
Last August I got this AU-D707X Decade amplifier here in Bangkok. The amplifier turned on, came out of protection, and it sounded good when we tested it at the shop. We used a pair of Yamahas NS1000 and a Marantz CD-63 CD player. I observed that all the functions work with the exception of the subsonic filter which did not engage when I pressed it. The amplifier has a little damage at the lower left corner of the particle board side panel. But the front and back panels are in good condition, and a quick look inside suggested that all the boards except for the regulated power supply (F-4292) did not get any noticeable work done on them. So I took it home and I had no time to do anything until now.
There are no threads discussing renovation and adjustment of the AU-D707X amplifiers, which are the Japan market equivalent of the AU-D11-II. Thus, I studied every thread I found in this site about the most similar units (AU-D11-II and AU-G90X). Big thanks to @Hyperion, @phonomac, @LWB and @leesonic for all their extremely valuable threads. A very useful site was the amp8.com, a company that repairs amplifiers in Japan which shows pictures of the units they repair. I wish to renovate this amplifier, so I start this thread to get advice from users with experience in this kind of amplifiers.
The first thing I did was to carefully inspect the unit internal parts, and had a close look at the F-4292 power supply. The board had damaged electrolytic capacitors, and a broken tab on the upper left corner. There were bulging electrolytic capacitors, a ceramic resistor, five delaminated/damaged solder pads on the solder side. So I decided not to power on the amplifier until I fix this board. Clearly somebody worked on this amlifier before. Unfortunately that person was not carefull or did not care about the unit very much... Here is a picture of the initial state of the power supply board:
For this board, the circuit diagram is the same as that fr the AU-G90X.
I removed all the electrolytic capacitors, and cleaned the glue.
I noted that on the -30V V rail, there was a 1N4007 diode installed in place of a constant current diode (10DY4.5). Thus, they found the need to install a 3W, 150Ohm resistor where there should have been a 33 ohm resistor rated at 1/2 watt. The 4.5 mA current regulating diode can be replaced by an E-472. I replaced both current regulating diodes. The installed zener diode in the -30V rail was a 1W version which has a Izener of 8.5mA. With the 4.5 mA current regulating diode in place, the zener diode is not working on the steep part of the I-V curve, so the negative rail would have less than -30 volts. So i replaced both zener diodes, using 0.5W diodes whose Izener is 4.2 mA so they would regulate the voltage properly. I installed non inflamable 33ohm and 10 ohm resistors where appropriate, and then put new electrolytic capacitors ased on what I had available. I used Panasonic FC 470 uF 63V for the unregulated power supply. For the regulated power supply, instead of the pair of 470uF 50V, I felt that there was no harm on using a pair of Nichicon UFG 1000uF 63 V which fit nicely in this location. The zeners were bypassed with Panasonic FC 100uF, 63V, and the output of the regulated power supply were upgraded from 100uF 35V to 220uF 63 V (Panasonic FC).
Then I fixed the delaminated pads, using 60minute epoxy glue. For the loose connector I installed some inserts using 60 minute epoxy to glue them in place.Once the epoxy cured, I filed the tubes flush with the top surface of the PCB and then soldered the cnnector back in place.
I fixed the broken tab by gluing a piece of pertinax using epoxy. Work still in progress. I will post more details after test this board.
Jose
Last August I got this AU-D707X Decade amplifier here in Bangkok. The amplifier turned on, came out of protection, and it sounded good when we tested it at the shop. We used a pair of Yamahas NS1000 and a Marantz CD-63 CD player. I observed that all the functions work with the exception of the subsonic filter which did not engage when I pressed it. The amplifier has a little damage at the lower left corner of the particle board side panel. But the front and back panels are in good condition, and a quick look inside suggested that all the boards except for the regulated power supply (F-4292) did not get any noticeable work done on them. So I took it home and I had no time to do anything until now.
There are no threads discussing renovation and adjustment of the AU-D707X amplifiers, which are the Japan market equivalent of the AU-D11-II. Thus, I studied every thread I found in this site about the most similar units (AU-D11-II and AU-G90X). Big thanks to @Hyperion, @phonomac, @LWB and @leesonic for all their extremely valuable threads. A very useful site was the amp8.com, a company that repairs amplifiers in Japan which shows pictures of the units they repair. I wish to renovate this amplifier, so I start this thread to get advice from users with experience in this kind of amplifiers.
The first thing I did was to carefully inspect the unit internal parts, and had a close look at the F-4292 power supply. The board had damaged electrolytic capacitors, and a broken tab on the upper left corner. There were bulging electrolytic capacitors, a ceramic resistor, five delaminated/damaged solder pads on the solder side. So I decided not to power on the amplifier until I fix this board. Clearly somebody worked on this amlifier before. Unfortunately that person was not carefull or did not care about the unit very much... Here is a picture of the initial state of the power supply board:
For this board, the circuit diagram is the same as that fr the AU-G90X.
I removed all the electrolytic capacitors, and cleaned the glue.
I noted that on the -30V V rail, there was a 1N4007 diode installed in place of a constant current diode (10DY4.5). Thus, they found the need to install a 3W, 150Ohm resistor where there should have been a 33 ohm resistor rated at 1/2 watt. The 4.5 mA current regulating diode can be replaced by an E-472. I replaced both current regulating diodes. The installed zener diode in the -30V rail was a 1W version which has a Izener of 8.5mA. With the 4.5 mA current regulating diode in place, the zener diode is not working on the steep part of the I-V curve, so the negative rail would have less than -30 volts. So i replaced both zener diodes, using 0.5W diodes whose Izener is 4.2 mA so they would regulate the voltage properly. I installed non inflamable 33ohm and 10 ohm resistors where appropriate, and then put new electrolytic capacitors ased on what I had available. I used Panasonic FC 470 uF 63V for the unregulated power supply. For the regulated power supply, instead of the pair of 470uF 50V, I felt that there was no harm on using a pair of Nichicon UFG 1000uF 63 V which fit nicely in this location. The zeners were bypassed with Panasonic FC 100uF, 63V, and the output of the regulated power supply were upgraded from 100uF 35V to 220uF 63 V (Panasonic FC).
Then I fixed the delaminated pads, using 60minute epoxy glue. For the loose connector I installed some inserts using 60 minute epoxy to glue them in place.Once the epoxy cured, I filed the tubes flush with the top surface of the PCB and then soldered the cnnector back in place.
I fixed the broken tab by gluing a piece of pertinax using epoxy. Work still in progress. I will post more details after test this board.
Jose