Question about Audio Players & Recorders
When I obtained the unit, the ouput protection relays chattered for the first couple of seconds after power up and then the output cut-out completely. Now there is no output at power on. With a scope I see the RF signal at the input to IC1 for both channels and see the signal at the left channel output of IC1( pin 6) but the right channel output of IC1 (pin 10) is sitting at -34 Vdc. I am looking for ideas on best actions to take to determine the problem and work to recovery. Thanks for any help offered.
Don't bypass the relay contacts. They serve to disconnect the amp stages from the speaker if a DC condition is present, and in doing that, save your speakers form damage. Check for a DC offset condition on the junction of the emmitter stabilizer resistors to the STK0040 on each channel. They will be 0.47 ohm power resistors(2 per STK) connected to pins 3 and 8 of the STK. Anything substantially greater that 100mv here generally indicates a blown STK. Don't bother to change both, but just the one that is faulty. Another common problem for this age of amp. The high silver content in the legs of the transistors allows for "growth" between legs and internal connections of the transistor. Check for "black death" on the legs of transistors driving the STK. . . I tend to replace them if in doubt. If you need expert advice, comment me back. I am an audio specialist.
Posted on Feb 03, 2008
Pleace schematic kenwood kr4010
Posted on Jun 18, 2008
In those days I found that it was best to bypass the relays as they caused a lot of output transistors and speakers to blow.
it was some stupid hot idea back then.
I am still running 2 marantz amps since 78 today that are wired across the relays.
the normal issue with these amps is usually always that the outputs transistors or output amps if IC are blown because of this . replace outputs and try again.
use headphones while troubleshooting.
If you want me to I will look at the schematic if you have one. I sold all of mine and threw a bunch away 10 years ago.
if you know of one online send me a link
Posted on Feb 03, 2008
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Posted on Jan 02, 2017
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It is possible that the amplifier had encountered a fault with a higher current drain which had triggered it to a protection fault condition. The fault can be with your output drivers. Please check for short on the outputs fitted for both the channels. Use a meter after disconnecting to check for short in the drivers. Disconnect the positive and negative voltages to the output and see if the protect changes. Even a fault in the preamp stages that drives in high current into the output can shut the Amplifier. Sometimes this can be a noise which can be a HUM or HISS before the protect works. Faulty capacitors in these circuits also can cause similar issues and needs close observation.You need to confirm and replace the specific stages or outputs. If not there can be issues in the mother board. Maybe the protect circuit by itself is shutting off due to a faulty bias or there is a leak in any voltage/current sensing circuit. Also disconnect the speakers and test, if the amplifier comes out of the protect mode then check for short on the speakers.
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