Yamaha CR-1020 Relay Flapping

with the power off the resistance of the collector of tr702 to chassis ground is 163 ohms

TR706:

E: 0V
C: 40mV
B: 0V
 
Relay coil is good. Check D718 and R744 (150KΩ) and R748 (47Ω)
 
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so, the relay is staying open. I get the following on TR702 referencing chassis ground.

E: 21.2V
C: -500mV
B: 21.2V
Could be shorted E-B.Or a solder bridge.
 
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C728 is the main filter capacitor for the DC to the protection relay. If you have marginal filtered DC the relay will act that way.

Craig
 
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I'm thinking you have a cracked trace or solder connection or even a lifted solder pad on your PS board.
 
I'm thinking you have a cracked trace or solder connection or even a lifted solder pad on your PS board.

I've been probing around for such an issue, continuity testing from solder joint to solder joint along the traces. I'm not coming up with anything. Is there a smarter way to do this?
 
What voltages do you see at the base of TR702 while the relay is toggling?
 
I had a similar issue with my CR-1020; intermittent popping from both channels and a bit of low level hum at initial turn on. Many many hours of troubleshooting, so wanted to share here in the hopes of saving others some heartburn.

After a full power supply recap (both pcbs) and power transistor upgrade to higher voltage TIP31C in the supply, the protection relay would not fire. The -25V output sat at -10V. Cleaned the flux and grime off the bottom side the PCB and the output went to +6V. Disconnected the two purple wires from the -25V post to eliminate loading. No improvement. Removed and retested all 4 transistors; junctions not shorted nor open.

Decided to look at the .01uF capacitors. In circuit across the terminals, the one on the -25V supply measured 6 kOhms whereas the one in the +25V supply measured 3 megohms. Pulled the caps; neither was leaky. Pulled the 4 transistors again. Still 6 KOhms...strange.

Used flux remover to clean the top side of the PCB around the .01uF cap locations, removing glue residue around the heatsinks. Resistance now 2 megohms. Apparently the glue that Yamaha used was not electrically benign and the -25V supply is extra sensitive to leakage current (check out the circuit topology).

Reinstalled all components. Reconnected all wires. Voltages perfect. Relay works.
—Ed
 
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