CR-820 Idling Current Adjustment Question

[TomHarrison1]

I've seen the other posts here about how to adjust idling current on an 820, but the posts and service manual are not completely specific in what test points to measure.

The manual says to turn VR701 and VR702, so that the voltages between TP1 and TP2, TP3 and TP4 become rated value as shown in right hand side (8+-2mV).

So does this mean measure current between TP1 and TP2 and turn VR701? Those 2 test points are next to each other, while TP3 and TP4 are legs of output transistors.

It seems to me that I should turn VR701 while measuring voltage across TP1 and TP3, and
turn VR702 while measuring voltage across TP2 and TP4. Can someone confirm this for me. Thanks.

 

[avionic]

So does this mean measure current between TP1 and TP2 and turn VR701?

No voltage ie millivolts 8mv +/- 2mv..

 

[avionic]

Those 2 test points are next to each other, while TP3 and TP4 are legs of output transistors.

That is correct.

 

[avionic]

. Can someone confirm this for me.

Confirmed.

 

[TomHarrison1]

So measure voltage across TP1 and TP3 and then measure voltage across TP2 and TP4?

 

[avionic]

So measure voltage across TP1 and TP3 and then measure voltage across TP2 and TP4?

No... Just like the service manual says .

 

[avionic]

TP1 and TP2 connect to the other channels output emitters. Just like TP3 and TP4.

 

[TomHarrison1]

Ah, I get it. Thank you.

 

[avionic]

Ah, I get it. Thank you.

Adjusting idle current ( milliamps )
Measuring millivolts across the two emitter resistors in both channels. Each emitter resistor is .22 Ω. .22 +.22 = .44 total resistance. 8mv is total voltage. Voltage divided by resistance equals current. ( 8mv/.44Ω= 18.18ma of idle current) good ol Ohms Law.