Yamaha CA-2010 enters speaker protection during warm-up

[OlaG]

I have a problem with a CA-2010 that I hope someone who understands a schematic could help me out with. I have done my best to read up on the various threads already available on the topic of CA-2010 going into speaker protection.

The relay clicks (closes) a couple of seconds after powering up, and all is good.
After a minute or two, the relay breaks both channels, and then typically remains open for anything from a few seconds to about a minute, maximum, and closes again. Then, as the amplifier continues to warm up, the relay can break one or two more times, but once the amplifier has reached working temperature, it works and plays.

I have replaced all electrolytic capacitors (on all boards), as well as the speaker protection relay. After some further consideration, however, it seems to be a semiconductor issue, considering the temperature dependence. Or perhaps a bad solder joint.
+B3 voltage from the power supply board is stable at about 11 V, which I presume should rule out problems with supply voltage to the speaker protection circuit? Also +/-B and +/-B2 are close to spec, if that matters.
The problem remains when the Pre-out switch is open, which I presume should rule out DC from pre-amp and tone control?
Voltages between TP1 and TP2, and between TP1 and TP3, have been set according to service manual when the unit is warm.

While the unit warms up, the voltage between TP1 and E on the right-channel main amp fluctuates slowly, but with a large amplitude (typically, a couple of 100 mV). Then, at some point, the voltage rushes rather quickly up to a few volts (up to about 10 V, max), and the protection relay breaks. As explained above, this can happen a couple of times during warm-up, until everything stabilizes after some 15 minutes or so. TP1-TP2 remains stable at 25 mV also while TP1-E fluctuates. The test-point voltages of the left-channel main amp do not fluctuate.

I guess this, in combination with the other tests described above, could point towards semiconductor components of the right-channel main amp. Is this correct? If so, does anyone familiar with the CA-2010 have any suggestions for which components would be the main suspects, or any suggestions on how I could proceed to narrow it down further? I sure can replace components, but unfortunately I’m not skilled enough in electronics to figure out how the circuitry actually operates in detail.
Thanks!

 

[mbz]

While the unit warms up, the voltage between TP1 and E on the right-channel main amp fluctuates slowly, but with a large amplitude (typically, a couple of 100 mV). Then, at some point, the voltage rushes rather quickly up to a few volts (up to about 10 V, max), and the protection relay breaks

Yeah most likely silicon, since problem is somewhat intermittent it will be a PITA to track down.
You will need to troubleshoot the right power amp board, this means removing the board/heatsink then reconnect the necessary power,audio,, wires using jumpers then measure dc voltages when the problem of high voltages occurs.

Since voltage is +ve (10Vdc) the test points working back would be TR319e then TR319b they should be +0.6V and +1.2V approx and stable.

edit thinking most likely that outputs or driver (TR321,3 and TR319) are breaking down, maybe test by using hair dryer or... to heat up the right channel heatsink/outputs then power up and monitor TP1 voltage. Other candidates would be TR307,8,9. Fusible resistors should be checked especially those on the -ve rail but unlikely cause since unit ok when warmed up.

 

[OlaG]

Thanks mbz, you pointed me in the right direction.

Voltages on TR319 were rock-steady, but your suggestion prompted me to check the voltages on TR320, i.e. what I understand to be TR319’s counterpart in the parallel path of a push-pull configuration, based on the assumption that those voltages should be the same as those on TR319.
It turned out that TR320 voltage fluctuated slowly but quite heavily.

I sat and waited for the DC voltage across TP1-E to get high enough to trigger the relay, partly to see what would happen on TR320 when TP1 voltage rushed, and partly to see if I could abort the rush by cooling TR320, or any of the nearby transistors, with cooling spray.
While waiting and watching the voltages, I did some maintenance on a thermostat valve, and at some point I tapped the valve onto the workbench to free a screw. This made the voltages on TR320 and TP1 jump around. Trying to tap a bit harder on the amp board stabilized the voltages.

After re-flowing all solder joints of the right main amp, with particular focus around TR320, it has not gone into protection. I have only tried one single cold start this far, however, so it might be a bit early for loud hoorays, considering the intermittent character of the problem. Tentatively, problem seems solved, though.
Thanks again.

 

[Sparkplug]

There are probably more bad solder joints on that board. Consider reflowing all of them to prevent similar failures in the future.

 

[Nashou66]

There are probably more bad solder joints on that board. Consider reflowing all of them to prevent similar failures in the future.

It still amazes me that most of the fixes is just a reflow . Most of us chase problems all over the place and THEN we decide to reflow the solder joints.

Im going to follow Sparky's consistent advice on numerous threads to reflow all solder joints first, and if the problem still persists then dive in deeper .

Nashou