Service Rotel Ra 11 Drivers Warm Up

Service Rotel Ra 11 Drivers Warm Up

The heatsink of three drivers warm up to about 55 degrees C, but one (Q623) warms up to over 70 degrees C.

I checked R641 (and R643) and they both measure the expected 1K ohms.

Replacing Q623 (I had a spare) didnt help.

Does it make sense to suspect the current mirror and or Q635 What are good equivalents for a 2SB361 Of course, I will replace them both.

You would check the base to emitter voltages of both of these in circuit with the power off.

The readings should be representative of what you would expect across a diode.

There was some DC offset on this channel (30mV, the other channel was fine, approx.

V) which I corrected.

The base at Q623 was at 1.18 V (compared to TP3).

The equivalent on the other channel measured the same (but the schematic suggests it should be 0.53 V).

However, measuring the temperature again, the situation appeared less asymmetric than before: Q637 was 71 C, equivalent on the other channel 67 C.

I take it you used the diode test function to check Q627 and Q629 base emitter junctions and the voltage range to test between base Q623 to TP3 under power without the speaker being connected.

I would be comfortable with driver temperature at 55 C if that applied to all 4 of them.

I recommend measuring the voltage drops across all the emitter resistors in the driver and output stages and work out the current levels.

The safest way to do that is to put the black probe into the black speaker terminal in that way you only have to use one hand with the red probe.

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Manual Service Rotel Ra 11