The KA-9100 power supply in stock form. (X00-1870-11) This is the K version of the power supply for North America. Foreign or multi-voltage supplies may differ.
Changes made to the KA-9100 power supply board (X00-1870-11) have been completed.
After the changes were made a DBT power on was performed. After a glow and dim on the DBT a full power up was performed. The amp took a full 20 seconds or more to come out of protection and the VU meters were reading 10W. Holy Moly, what's going on here? Rather than panic I applied the KISS method. I know it worked fine before working on this board so it has to be something wrong with the supply. After a thorough recheck of every component changed I was confident nothing was replaced incorrectly. I turned my attention to the bottom edge of the board to see if there were any broken wires and again found nothing wrong. As I was moving the board looking things over I spotted pin 25, the -B supply, had a cracked solder joint. Bingo. I re-flowed all the pin joints just as precaution and then powered up again. After 3 or 4 seconds, PING! relay engaged.
The KA-9100 power supply with new components installed.
Rk11 1K 2W was replaced with a 3W metal film and given strain relief. The two stock 470ohm at Rk2 and Rk4 were replaced with 1W KOA Speer SPR Carbon Film replacements ( I believe the originals may be flameproof type so I went with the SPR which have flameproof coating ) and their leads given strain relief. All the other resistors were replaced with the 1% .5W metal film. I made point to raise the 820 ohm Rk1 and Rk3 off the board a bit for better heat shedding. All the W06B diodes at Dk1-5 were replaced with 1N4007G rectifiers, raised a little off the board. The YZ-140 at DZk1 was swapped for a 1N5244B Zener.
There are ten electrolytics here.
Ck11 4.7uf 35v (25v actual) > MKS2 4.7uf 50v
Ck14 47uf 16v 8mm > 47uf 25V RFS 8mm
Ck8 47uf 35v 10mm > 47uf 35V RFS 10mm
Ck6 47uf 50 10mm > 47uf 50V KZ 10mm
Ck10 10uf 25v > 10uf 50v FC
Ck5 100uf 50v 12.5mm >100uf 63V PM 12.5mm
Ck12/13 220uf 35v 12.5mm > 220uf 50V FC 12.5mm
Ck3/4 470uf 50v 16x35mm > 560uf 63V HE 16x30mm
The four transistors were replaced as follows
2SC1983 > MJE15032G
2SA755 > MJE15033G
2SA673 > KSA1220A
2SC945 > KSC945CGTA
There are some points of interest to working on this power supply. It should be noted that Ck16, a 47 picofarad ceramic cap, is on the rear of the board. It is soldered across the collector and base of Qk4 2SA673. If you replace Qk4 you'll need to remember to put this cap back in place. My board had glue over the solder joints so you may need to remove that first.
Ck16 47pf
Also of note, the regulators at Qk1 and Qk2 are mounted to heatsinks which mount to the bottom of the PCB. During removal it was obvious that all of these screws were very loose and might have easily come unscrewed given time. Whether you replace these transistors or not I would suggest tightening them up and adding some thread lock to prevent any of them from falling out. These same transistors also did not have any thermal compound on them. I would suggest adding a thin layer for better heat dissipation.
Thread lock is added to the transistor mounting screw. Some should also be applied to the board mounting screw.
A thin layer of thermal compound is applied between the regulator and heatsink prior to mounting.