I'll check that now and give you an answer... and thanks very much for all the help!!! Really appreciate it!!!
No it is 1 of Q3 is 24vdc 3 is 66vdc and 2 (which is the base, isn't it?) is 12vdc. That's really bad, isn't it?
Tried to test voltages again: when power on- Q3, C=24vdc, E=24vdc, B=24vdc; Q1, C=24vdc, E=24vdc, B=24vdc. There is no 0.7 vdc. Voltage in R89 (19.1 k ohms) dropped from +66vdc to 24 vdc.
OK, the 66vdc had me concerned the first time. This thing should be working if the STK4050 is good and the signal is getting to pins 1 and 2 . I'm sure you have probably double checked your source input connection to the sub..Oh,by the way Mouser Electronics has some 19.1 K ohm 1/2 watt metalfilm resistors P/N 660-MF1/2CL1912F the schematic states 1/2 watt so it should be satisfactory.Mouser also has no min. purchase amount.
You don't by chance have a oscilloscope?
Dave
You don't by chance have a oscilloscope?
Dave
As far as R89 goes I'd stay with what you have the 2 resistors in series. A 1/2 watt appears to be on the threshold of being to small.Judging from other posts.
Sorry, I don't have an oscilloscope. Yes, I have checked all the connections on the STK4050V from pin 1 to 18 (except 6- it's not connected).
Will it be possible if I get the signal from pin 1 (input) of the STK4050V and connect it to an external amplifier and see if that'll work? Then I know my STK4050V is at fault.
Will it be possible if I get the signal from pin 1 (input) of the STK4050V and connect it to an external amplifier and see if that'll work? Then I know my STK4050V is at fault.
No luck. There's no signal coming to the output stage of the amplifier. Can an IC (U1: LF347N) in the trip point be at fault?Another question please: is there really a DC voltage coming out of the speaker terminals, like 10 volts? Almost ready to give up on this amp. But I'll still wait for any assistance and recommendations. Thanks.
Do you mean there is no signal at the input to the STK4050 ? If there is no input then there is no output
No not unless there is a problem.Ideally 0 volts ,reality 10-20 mv. IC U1 looks like a pair of OPamps if those amps are not working properly you would not get - poweron but we appear to get -poweron because you measured 24vdc on the collectors of Q! and Q3 satisfying the ( disabling mute and enabling poweron. To me it looks like a problem in the Limiter or the Limiter low pass or the output amplifier stage. Need to check all of the IC's in that signal path to make sure they are getting (VCC power) U1,U2 ,U6,& U7.
IC U1 appears to be a quad opamp it uses two parts in the (trip point circuit and the other two are used in the limiter section.
Dave
Sorry, it took a long time to post. I think I made a mistake taking pin1 of the STK 4050V as the input. When I tried to see the schematics again, I realized the input signal is in pin 2 which is connected to the "power-in." Pin 1 is to gnd and the (+) and pin 2 is the (-) but receives the signal. I'll try again hooking this to an external amplifier and see what'll happen. Hope it works so then I'll know the output stage (STK4050V) is at fault.
No problem! Power-in is a strange nomenclature for a audio signal input point,it threw me off when I first glanced over the circuit --assumed it to be power supply input at first.Anyway let me know what you find out.
Dave
Dave
Sorry. No luck. There is signal coming to pin 2 of the STK but when I attached it to an external amplifier, still no sound...just a hissing sound. Yes, I turned the volume up.
Anyone with any idea... I'll really appreciate it.
Anyone with any idea... I'll really appreciate it.
Yes, finally I was able to connect the preamp to an external amplifier. It sounded like the original except I had to put the volume to 1/2 the setting. There is also one thing I noticed: my external amplifier is warming fast. Is this normal? By the way, the input to my amplifier is registering 6-7 vdc, I think this is not normal but if anyone can share their thoughts on how to cut or why this voltage, I'll appreciate the opinion. Thanks in advance.
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