The power out from 60Vpp is:
56.25W per channel into 8 ohm
Hmm..no schematic? No phono input so no pre amp, so first amp is 8 pin JRC7004E - tests ok at pins 1 and 7 ouputs.
STK4171V/STK4181V/STK4191V - ECG1317
Audio Power Amp, 50 W, 8 ohms, Vcc = +/- 35.5 V, 18 pin SIP. Pin 1: Left channel input (-) Pin 2: Left channel input (+) Pin 3: Compensation Pin 4: Compensation Pin 5: Compensation Pin 6: Muting Pin 7: Compensation Pin 8: Compensation Pin 9: -Vcc Pin 10: Left channel Output Pin 11: +Vcc Pin 12: Bypass Pin 13: Right channel output Pin 14: -Vcc Pin 15: Compensation Pin 16: Gnd Pin 17: Right channel input (+) Pin 18: Right channel input (-)
Odd readings on the only 8 pin op amp (Mitsubishi 5218A) by the tone controls, so will remove and test it..op amp ok. Something is dragging down the negative side of this op amp to just above ground, and seems linked to the faulty direct/mute switch circuits, but components there test ok, with correct voltages as shown on circuit.
Been through the vol board voltages from schematic to find why the output of pin 10 is 0.5V not 2.5V, with full 7.8V B+ line at the 10k resistor R200 - the diode D109 was changed but checked ok:
This B+ line also feeds the mute and source transistors (22k resistors built in and pricey at -£3.50 each!), that also don't work, after changing the LEDs and the BA1F4M transistors from with good ones from the input switch circuits - though one tranny was probably duff - but didn't solve their no switching fault. I removed the MC14052 mux chip and ordered a new one, adding a chip holder. If it's not that I'm stumped..
10/10/202
This is the biggest pain amp I've ever had! I cannot find this fault! Something dragging the voltage down somewhere to cause B+ at pin 7 out of the op amp and for the mute/source circuits to not switch...The tracks are bastards for coming away when desoldering, totally sick of it now...