Here is a weird issue ...
--Upon power up time delay , protection sequence , fault leds all work properly
--Inject 1KHZ makes signal present leds lit but no matter how hard you drive there is no clip and no output
--Rail voltage is present
--secondary voltages are present
--signal van be traced up to the input of the board with no issues but seems that gets lost on the Vas stage of the amp
--All diodes especially the ones related in the protection and VI limiter area measure properly DVM check on diode and all small BF transistors present normal readings On board DVM diode check
Both ch present the same issue
here is a schematic
--Upon power up time delay , protection sequence , fault leds all work properly
--Inject 1KHZ makes signal present leds lit but no matter how hard you drive there is no clip and no output
--Rail voltage is present
--secondary voltages are present
--signal van be traced up to the input of the board with no issues but seems that gets lost on the Vas stage of the amp
--All diodes especially the ones related in the protection and VI limiter area measure properly DVM check on diode and all small BF transistors present normal readings On board DVM diode check
Both ch present the same issue
here is a schematic
obviously and forgot to say ...amp looks brand new there is no soldering or pcb issues and there is no resistor appears to be open since 1% measure all properly and especially the small ones like 56-220 R
Kind regards
Sakis
Kind regards
Sakis
John thanks for joining
U4 is the IC that handles the balanced input as said signal can be properly traced to the input of the amplifier ( differential stage ) C124 and 224 so i don't think that i have any problems there
U4 is the IC that handles the balanced input as said signal can be properly traced to the input of the amplifier ( differential stage ) C124 and 224 so i don't think that i have any problems there
What have you got on E1 and E2. Should be zero DC with no signal and there should be AC with signal input
It's a bit sad, that the display schematic is missing, so it's not easy to recognize, where this LED get the signal....
Sajti
Sajti
E1 and E2 are the power output buss where the emitter resistors from the power transistors connect together. The hot end of the large RF coils. If you have signal at the input of the amp with good rails and ground with no output on the power output busses, some measurements are not quite right.
As said John ...signal is getting traced around the input stage of the amplifier ( both CH ) directly on board but is getting lost after the VAS stage
DC on E1 or 2 will be found by the protection circuit and trigger protection circuits and this is not happening output is a total zero in both DC and Ac aspects
DC on E1 or 2 will be found by the protection circuit and trigger protection circuits and this is not happening output is a total zero in both DC and Ac aspects
I never presume, always take a measurement. It saves time and points the direction to go.
Both channels? very odd. I need to fault find really. It will be a common voltage missing I expect.
Good luck with it.
Both channels? very odd. I need to fault find really. It will be a common voltage missing I expect.
Good luck with it.
If the "Signal presetn" LED gets the driving signal from the output of the power amplifier, that help us to find that the power stage is working. If this LED gets the signal from the input module (not a common solution) than the power stage may not work.
Did You hear the output relay "click" after the turn on delay?
Sajti
well ...solution comes directly from Crown thanks to DEREK HOLLOWAY and actually is more than a procedure issue rather than a real failure .
Experienced tech will check firs all voltage present , DC in the output, start up sequence : time delay and so on , Secondary voltages present and so on .
The next step is fusible or low in Ohms resistors starting from a few ohms till 220 Ohms or so ...
In this case there is plenty of them as can be seen in the schematic , WHILE A RESISTOR WITH NO VALUE ON IT is easy to overlook ...
R105-205 is a resistor without a value on the schematic since the specific resistor Value will change depending on the model of the amplifier ...
Both of them were open ( totally ) resulting that the upper part of the LTP to not operate at all ...
Been also told that this is a common failure for this type of amplifiers and the specific resistors should be a bit stronger than 0.4W metal film
So i did used FP 47K of 1W and done
Thanks all of you for the help specially Derek !!
Kind regards
Sakis
Experienced tech will check firs all voltage present , DC in the output, start up sequence : time delay and so on , Secondary voltages present and so on .
The next step is fusible or low in Ohms resistors starting from a few ohms till 220 Ohms or so ...
In this case there is plenty of them as can be seen in the schematic , WHILE A RESISTOR WITH NO VALUE ON IT is easy to overlook ...
R105-205 is a resistor without a value on the schematic since the specific resistor Value will change depending on the model of the amplifier ...
Both of them were open ( totally ) resulting that the upper part of the LTP to not operate at all ...
Been also told that this is a common failure for this type of amplifiers and the specific resistors should be a bit stronger than 0.4W metal film
So i did used FP 47K of 1W and done
Thanks all of you for the help specially Derek !!
Kind regards
Sakis
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