lilviper wrote:Ok, I'd love some direction on replacement parts.
Q111 is 2SC1567 and the legs were cut, can't find too much information on that transistor apparently its NLA.
Q114 and Q115 are missing.
Q117 is a 2SA1659A which doesn't match any other transistor on the board so it's got to be a replacement.
Q116 has been changed but I didn't write down what transistor is there.
D101 was removed and replaced, probably to verify that the problem is not a dead LED.
The jumper wire with the resistor is odd.
There are no burned traces other than one of the power supply caps, and none of the resistors look like they got hot, other than what was replaced in front of Q121.
Any suggestions on test points and their values?
Q111- I use KSC2690A as a sub, KSC3503 will also work, but I typically save those for the amps with higer rail voltages. Both parts are currently backordered at the major US suppliers. Mouser shows they should be getting about 5,000 in November, I would get on the list if you want them. They go quickly.
Q114- is supposed to be 2SC5248E; You should be able to use 2SC4883A-- I have not tried these, but they are a good match on paper. I still have a fair supply of the stock drivers and another driver that I use to sub, but both are obsolete now.
Q115- is supposed to be 2SA1964A; You should be able to use 2SA1859A, same caveat as above. Both of these particular transistors are available at digikey. Mouser had nothing suitable is the TO-220FP package.
Q116-is supposed to be 2SC5248E; Same as above for Q114
The 2SA1659A/2SC4370A pair are suitable replacements although their bandwidth is only 2/3rds of the stock parts. They are also long obsolete, and the Sanken transistors I recommend above are much closer to the stock parts.
Q117-is supposed to be 2SA1964A; Same as above for Q115
The red LEDs are used to provide a specific voltage drop for the bias of each channel. If it needs replaced, you need to measure the voltage dropped across one of the LEDs which are working and buy a red LED with a published spec that matches that voltage for it's forward voltage. Alternatively I believe there are two unpopulated diode locations near the LED, you can remove the red LEDs entirely and use two 1N4148 diodes in series in their place. As long as the voltage drop across the pair of LEDs per channel are close to the same, it will function properly. The same goes for a pair of diodes if you go that route, the drop across each set in a channel should be as close to the same as possible. Do not try to use a resistor in this location to provide the current source, a resistor will shift to much with heat. It has to be an LED or pair of diodes. Also, the color was chosen for it's particular forward voltage. If you get the notion to change them to a prettier color-- don't
.
Good Luck,
Jason
