Yamaha RX-730

[ve ze]

No, you got it right, it is the correct jumper. The same 2mV on the IC7 pin16.
Is D15 the next for a check?

 

[mbz]

same 2mV on the IC7 pin16

Recheck replaced R230, R231, signs of stress. Try measure in-circuit.

Suspect Q36 has died, measure dc voltage one side of R217. Repeat for other side R217.
Alternatively measure at zener and rectifier output, ie, measure 1 red point and one blue.

 

[audiotemp]

Also possible that the zener (D13) or even possibly the cap (C162) are shorted or leaking, holding the base of Q36 low. But the above measurements should make it clear.

 

[ve ze]

Recheck replaced R230, R231, signs of stress. Try measure in-circuit.

Suspect Q36 has died, measure dc voltage one side of R217. Repeat for other side R217.
Alternatively measure at zener and rectifier output, ie, measure 1 red point and one blue.

R230, 231 seem to be fine, both ~1ohm.
R217 both sides = 20mV then drops to 8 mV
Q36e = 8mV. In-circuit testing of this NPN Q36 (without power) with the MM doesn't comply with the usual OL between EC, B black to C red, B black to E red.
still figuring out how to get to the zener D13 and the rectifier D15 safely.

 

[mbz]

R217 both sides = 20mV then drops to 8 mV

One side of R217 should be rectifier (D15 bridge) output, nominal +15.6Vdc. Can't blame D13.

Maybe you have a burnt track? C177 failed (unlikely) D15 failed (unlikely, surge currents are normall xxAmps)

Previously we lifted 2 jumpers to the power amp, anything else still lifted?

 

[mbz]

Try measureing Vac (black probe to chassis) at one red point, repeat for one blue point

 

[ve ze]

Try measureing Vac (black probe to chassis) at one red point, repeat for one blue point

11.8V both
Nothing else lifted.

 

[audiotemp]

Maybe you have a burnt track? C177 failed (unlikely) D15 failed (unlikely, surge currents are normall xxAmps)

You mean C164, not C177 ?

If there was a sustained downstream short, D15 from both inputs to "+" could open. It's a 1A part while Q36 is likely 2SD1913 at 3A.

 

[mbz]

You mean C164, not C177 ?

yeah C164.

If there was a sustained downstream short, D15 from both inputs to "+" could open. It's a 1A part while Q36 is likely 2SD1913 at 3A.

With amp powered off try diode testing D15. Red probe on either ac symbol, black probe on the + symbol. Repeat for the other ac symbol and +, expect 0.55-0.7V

 

[ve ze]

D15 : ~ to + : 0.54V
~ to - : 2.26V
Tested with both ~ of the two pins. Same results.

 

[mbz]

~ to - : 2.26V

For the -ve rail need red probe on - symbol, black probe on ac symbol.

+ve rail looks fine

With only a few mV on R217 I'd be swayed by C164 but that's a sucker bet.
Has C164 been replaced?

suggest diode test D13,
red probe cathode, blk anode gives OL
red probe anode, blk cathode gives 0.55V

 

[ve ze]

Has C164 been replaced?

suggest diode test D13,
red probe cathode, blk anode gives OL
red probe anode, blk cathode gives 0.55V

C164 looks like factory solder.
red probe cathode, blk anode gives OL ----- actual 1.2V
red probe anode, blk cathode gives 0.55V ---- actual 0.74V

 

[mbz]

red probe cathode, blk anode gives OL ----- actual 1.2V

Incircuit test of D13 can be a bit tricky since you are testing across C162, would have expected the voltage to climb up as the MM charges up C162 eventually OL. Can't explain 1.2V, maybe it collapses to near zero at higher voltage?

Plz remove or lift one leg and retest

 

[ve ze]

OL with one leg lifted.

 

[mbz]

red probe cathode, blk anode gives OL ----- actual 1.2V

OL with one leg lifted.

Have to replace C162(100/16V), I'm a little sceptical however it matches the measurements...

I'm not totally convinced about D15, ok it passed diode test but...
If you have some spare time, lift marked leg of R217 then measure Vdc also measure Vac at the lifted leg, trying to test D15, ok there will be no current flow...

 

[mbz]

R217 both sides = 20mV then drops to 8 mV

Suggests problem is with C164 or D15. Post #136 should confirm this.

 

[ve ze]

According to the SM, C164 should be 3300 uF 25V. I tested it in ckt. It measures at 3034 uF which is 8% less. Still needs to be swapped? Or should I remove and recheck?
As for D15, AC is measured by one probe on the chassis, one on either of the ~ pins on D15. And DC is measured between + and - pins on it?

 

[mbz]

DC is measured between + and - pins on it?

Measure DC with black probe on chassis/GND then red probe on + pin.
Then repeat but red probe on - pin

Have to replace C162(100/16V),

C162 should be replaced because of inconsistent results when testing zener D13

C164 should be 3300 uF 25V. I tested it in ckt. It measures at 3034 uF which is 8% less. Still needs to be swapped?

I would not rush and replace look at D15 again

 

[ve ze]

C162 (100uF/16V) replaced. BTW, the original out of ckt measures at 85 uF.
D15 voltage:
AC 11.72 V this is consistent with #128
DC + or - both very close to 0 V.

 

[Nashou66]

C162 (100uF/16V) replaced. BTW, the original out of ckt measures at 85 uF.
D15 voltage:
AC 11.72 V this is consistent with #128
DC + or - both very close to 0 V.

This looks bad, there should be some output there, Right @mbz ?