I got one of these crazy things. it is totally dead. it had bad FETs in the power supply. i replaced those. amplifier is still dead.
Did some quick tests, i noticed that pin16 of the 494 was up around 8volts? i cant remember exactly. but pin15 was at 5v. so i knew there was an issue right there.
I temporarily shorted those 2 connections with a meter probe, and the amplifier came on, green LED. and it appeared to work fine. let off the short, amplifier goes back out.
checked drivers and stuff for leaks and shorts. appears ok. I found a transistor that is in the pin16 circuit that was shorted beforehand. replaced it.
it was a KTA1266 i think.
Anyway, the plot thickens more confusingly. If i hook the speakers up in bridged mode, amplifier will power on if i short pin16 and 15 again, however it stays on. but NO power LED or protect LED is lit, but the amplifier is playing. I can remove the short and it still plays. and i have about 5V at pin16 while playing. But it doesnt sound as good, distortion a slight bit, plus one side of the amp on the power supply FETs get hot. soon as i remove the speaker connection while amp is playing, it goes out. if i reconnect speaker, its dead again until i make that short. then itll power back on with no green LED and play again.
If i hook the speaker to just the left or just the right, the amp works if i make the short, WITH a green LED. and goes out when i remove the short. If i hook both speakers up to left and right, its a 50 50 shot. sometimes if i make the short, it will power on with green LED and the amplifier hits very hard. works fine appears to anyway...
but other times itll power on with no green LED and stay on, even if i remove short. but the amplifier doesnt sound near as strong, and clips alot sooner at lower volume, only while it is in this certain condition. if i can power the amp on when the gren LED comes on, everything works as normal. but for some reason the amp goes in this weird state.
Any ideas? i am confused with this one. why is it doing this?
Did some quick tests, i noticed that pin16 of the 494 was up around 8volts? i cant remember exactly. but pin15 was at 5v. so i knew there was an issue right there.
I temporarily shorted those 2 connections with a meter probe, and the amplifier came on, green LED. and it appeared to work fine. let off the short, amplifier goes back out.
checked drivers and stuff for leaks and shorts. appears ok. I found a transistor that is in the pin16 circuit that was shorted beforehand. replaced it.
it was a KTA1266 i think.
Anyway, the plot thickens more confusingly. If i hook the speakers up in bridged mode, amplifier will power on if i short pin16 and 15 again, however it stays on. but NO power LED or protect LED is lit, but the amplifier is playing. I can remove the short and it still plays. and i have about 5V at pin16 while playing. But it doesnt sound as good, distortion a slight bit, plus one side of the amp on the power supply FETs get hot. soon as i remove the speaker connection while amp is playing, it goes out. if i reconnect speaker, its dead again until i make that short. then itll power back on with no green LED and play again.
If i hook the speaker to just the left or just the right, the amp works if i make the short, WITH a green LED. and goes out when i remove the short. If i hook both speakers up to left and right, its a 50 50 shot. sometimes if i make the short, it will power on with green LED and the amplifier hits very hard. works fine appears to anyway...
but other times itll power on with no green LED and stay on, even if i remove short. but the amplifier doesnt sound near as strong, and clips alot sooner at lower volume, only while it is in this certain condition. if i can power the amp on when the gren LED comes on, everything works as normal. but for some reason the amp goes in this weird state.
Any ideas? i am confused with this one. why is it doing this?
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ill have to go through them again, but the pin16 had roughly 8 to 9v on it. while pin15 had the 5V reference. if pin 15 and 16 are shorted together physically with my probe, amp will power on and work properly. good sound, hits hard, etc etc.....
until i remove the short. then it shuts back down. but depends on how im loading the outputs, if i hook 1 speaker up bridge 4ohm, the amp will kick on when i short the pins15 and 16 together, but it wont shut back off if i remove the short, but the amp doesnt work correctly either.... like i said its very odd...
until i remove the short. then it shuts back down. but depends on how im loading the outputs, if i hook 1 speaker up bridge 4ohm, the amp will kick on when i short the pins15 and 16 together, but it wont shut back off if i remove the short, but the amp doesnt work correctly either.... like i said its very odd...
yea. when i get back to the shop tomorrow ill post a photo. its odd how its acting. im sure your just as confused as I am.
But like i said if i short out the inputs of the second error amplifier, the amp runs fine. until i bridge it, itll half-run. and one half the power supply starts to overheat. but both sides of FETs and driver xistors are tied together right at the TL494. also has 2 transformers in it.
its almost like 1 side shuts down but the other side is going. its impossible though because they are both connected together at the same points on the same 494.
But like i said if i short out the inputs of the second error amplifier, the amp runs fine. until i bridge it, itll half-run. and one half the power supply starts to overheat. but both sides of FETs and driver xistors are tied together right at the TL494. also has 2 transformers in it.
its almost like 1 side shuts down but the other side is going. its impossible though because they are both connected together at the same points on the same 494.
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