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Szép napot kívánok! A szóbanforgó erősítő javitásánál megakadtam, semmi hibát nem találok és mégis időközönként oltári sípolásba kezd mid a két csatornán. Mi okozza ezt ? Köszönettel :arpinyo

Original problem is no sub woofer output. Been through this one and recapped it and the common 2 burned 1K (R16/17)
resistors are replaced but the sub is still not responding. Volume control potentiometer is a common issue on these but
the L-R spkrs sound good.

Went by this webpage on the repair:
https://christopherbradshaw.net/The_Project_Bin/klipsch%20promedia%20subwoofer%20repair%20-%20page%201.html

On the schematic there is a sub-relay (sw101) powered by +V_HF line it
maybe is suppose to be +V_LF ? Without the relay coming on looks like the sub is disconnected.
The zeners (D03/04) that give +/- Vcc to the op amps seemed way off so I replaced them and the voltages seem much closer.

Theres also a sub-mute line on p104 to p101. Power supply shows the LF mute relay and interconnect diagram says it
gets fed from the LF amp. What is triggering the mute? I dont see a mute button anyplace.

Hi - I have a pair of KRK VXT4 studio monitor speakers. Very expensive! When I stored them, they were working fine. When I tried to use a few days ago, one of them simply hums loudly at 50Hz. I have tried replacing the two 12000uF PSU capacitors, as I found on Google that sometimes they can become depolarised but this has not solved the problem. I am trying to find a schematic for both the main board (which has the PSU and the PA stage) and the pre-amp board. - Thanks, Kevin

Sziasztok ! A fenti IC adatlapján a sensivity értéknél mit jelent ez TBD microvoltban kifejezve ! Más hasonló ic esetében 1,3 és 1,4 értékek szerepelnek ! Már volt dolgom
hasonló FM ic-vel azok kielégítő érzékenységgel  rendelkeznek  de a fenti készülékben lévő nagyon gyenge tudni szeretném hogy érdemes-e cserében gondolkodni !