Yamaha CA-810 Relay Randomly Engages

[Sparkplug]

Agree, that this is most likely. Certainly the OP should be checking solder joints and trackwork in the protection area. This fault will then cause a spike in dc offset or a dip in the relay supply. The measurements are about trying to identify the path that's causing the fault. If it's only dropping out once in an hours or so then this technique is worthless. If there is some predictability then it should help.

Totally agree …

 

[AngelAT]

Just out of curiosity, have you set/completed all the adjustments (not including the meter) correctly?

I did check and fixed the 20mV, the Lo and Ro double checked now and they are 0 vDC and ca. 4,5 VAC

 

[AngelAT]

I'd start with the above - some meters (eg. Fluke) have a min/max function which you can use to monitor DC offset (need to monitor at test points or emitter resistors, not speaker terminals). If the relay is disengaging due to momentary DC, it will be almost impossible to see while watching, whereas a capture device will show the spike.

You need to establish whether the relay is disengaging due to DC offset or a protection circuit issue, this would be the first step in troubleshooting.

My experience also. Doesn't hurt to replace, but very rarely the actual problem.

My VMs are basic and do not have the option for min/max, but checking the resistors and relay (soldered test wires) was not able to observe any anomalies there
Will continue investigating.

 

[AngelAT]

The problem is that I observe this strange behaviour once in an hour or two...
Reflowed the some parts of the power amp board again and now waiting.

 

[Sparkplug]

I did check and fixed the 20mV, the Lo and Ro double checked now and they are 0 vDC and ca. 4,5 VAC

Great job.
What is ca.? Circa? 4.5VAC?
Also, along with following what @mbz suggested above, do you have access to freeze spray? If yes, then maybe you could use small amounts on different parts of the board to see if that induces the clicking. It may not show anything but if there’s a crack somewhere, it could point it out or at least it’s whereabouts …

 

[Sparkplug]

One more thing I keep forgetting to ask, what are you using for your input source? Tuner? Phono? Aux? Does it matter? This happens with no input at all (everything disconnected) too? Probably shouldn’t matter anyway, just trying to get an idea on the whole setup …

 

[AngelAT]

Hello Sparkplug,
Yes, around 4 VAC.
And 0 VDC.
I used the freeze spray a few times now, spraying mainly on transistors and nothing...(I will also check other components)
I observe this with no inputs connected and also when using the AUX
Strange, right...

 

[AngelAT]

I can confirm that the problem is still present after reflowing the right channel again. Tapping and bending the board does not seem to change the status.
Any other ideas?

 

[zaibatsu]

You need to establish whether the relay is disengaging due to DC offset or a protection circuit issue, this would be the first step in troubleshooting.

As far as I can read, it has not yet been established whether DC offset spikes are triggering the relay or not.
When the relay opens, is it momentary, or does it stay open for longer than the usual turn-on delay time (i.e. time taken when amplifier is first turned on)?

I would connect your meter leads to a point before the relay where you can measure the DC offset (need minigrabber leads) and try to monitor the reading at a time when the relay opens.
If a DC spike is triggering the opening, the problem is likely to be in the amplifier section.

It is hard to isolate the problem area without this simple test.

 

[Sparkplug]

It might sound silly but have you checked your speaker connections (cables, cable wires/connectors)? Even one strand of wire touching the chassis could cause this. Does pulling/lifting the speaker cables (where they meet the RCA input connectors) induce this problem? Just eliminating possible physical causes … these are some obvious and easy checks to make alongside more detailed DC offset and relay voltage measurements.

 

[willyrover]

As far as I can read, it has not yet been established whether DC offset spikes are triggering the relay or not.

I would connect your meter leads to a point before the relay where you can measure the DC offset (need minigrabber leads) and try to monitor the reading at a time when the relay opens.
If a DC spike is triggering the opening, the problem is likely to be in the amplifier section.

It's useful to set the meter or use a meter that will HOLD the MAX reading.

 

[AngelAT]

As far as I can read, it has not yet been established whether DC offset spikes are triggering the relay or not.
When the relay opens, is it momentary, or does it stay open for longer than the usual turn-on delay time (i.e. time taken when amplifier is first turned on)?

I would connect your meter leads to a point before the relay where you can measure the DC offset (need minigrabber leads) and try to monitor the reading at a time when the relay opens.
If a DC spike is triggering the opening, the problem is likely to be in the amplifier section.

It is hard to isolate the problem area without this simple test.

Thanks!
Where do you advise to do the measurement?

 

[AngelAT]

It might sound silly but have you checked your speaker connections (cables, cable wires/connectors)? Even one strand of wire touching the chassis could cause this. Does pulling/lifting the speaker cables (where they meet the RCA input connectors) induce this problem? Just eliminating possible physical causes … these are some obvious and easy checks to make alongside more detailed DC offset and relay voltage measurements.

Thank you for the idea!
Will check this

 

[AngelAT]

It's useful to set the meter or use a meter that will HOLD the MAX reading.

I am not sure if I can do that with my MMs

 

[mbz]

Where do you advise to do the measurement?

Schematic shows RO and LO are the outputs from the relay. When a fault occurs the relay opens so RO and LO are no longer connected to the power amp. The preferred place to measure is between the emitter resistors on the power amp board, ie, R469, R471(left ch) and R470 and R472(Right). These are 0.47ohm 5W, typically large-ish white(cement) rectangular near the output transistors. hifiengine sm is not real clear, ideally measure where R469(R470) connects to R471(R472). If that difficult then measure at R469(L) either side and R470(R) again either side.

 

[AngelAT]

Schematic shows RO and LO are the outputs from the relay. When a fault occurs the relay opens so RO and LO are no longer connected to the power amp. The preferred place to measure is between the emitter resistors on the power amp board, ie, R469, R471(left ch) and R470 and R472(Right). These are 0.47ohm 5W, typically large-ish white(cement) rectangular near the output transistors. hifiengine sm is not real clear, ideally measure where R469(R470) connects to R471(R472). If that difficult then measure at R469(L) either side and R470(R) again either side.

Hi MBZ,
I am measuring both ends of the emitter resistors - soldered short wires to be able to connect the MM. Both are within spec - pls check post 14. I have set them to 20mV and they have drifted a bit so as you can see they stay constant when the relay starts engaging.
The other video is the voltage at the coil of the relay - again seems stable.
RO and LO are 0v.

 

[mbz]

I am measuring both ends of the emitter resistors - soldered short wires to be able to connect the MM. Both are within spec - pls check post 14

Apologies, I haven't followed this thread closely.

I'm now a little confused, thought the problem was related to DC offset. Bias is measured at both ends of the emitter resistors. Monitor dc offset by putting red probe at emitter resistor(post #35) and black probe to chassis/GND. Now to read post #14.

 

[AngelAT]

Apologies, I haven't followed this thread closely.

I'm now a little confused, thought the problem was related to DC offset. Bias is measured at both ends of the emitter resistors. Monitor dc offset by putting red probe at emitter resistor(post #35) and black probe to chassis/GND. Now to read post #14.

No need to apologise!
I would think the same way.

 

[AngelAT]

Schematic shows RO and LO are the outputs from the relay. When a fault occurs the relay opens so RO and LO are no longer connected to the power amp. The preferred place to measure is between the emitter resistors on the power amp board, ie, R469, R471(left ch) and R470 and R472(Right). These are 0.47ohm 5W, typically large-ish white(cement) rectangular near the output transistors. hifiengine sm is not real clear, ideally measure where R469(R470) connects to R471(R472). If that difficult then measure at R469(L) either side and R470(R) again either side.

Now I am a bit confused by what I measure...

I measure the following:
Both ends R469 19.8 mV
GND and Emitter end of R469 25.2 mV
GND and Link w. R471 5.3 mV

Both ends R470 17.6 mV
GND and Emitter end of R470 41.7 mV
GND and Link w. R472 24.1 mV

If I understood the Sm, I thought I should measure both ends of the em. resistors.

 

[mbz]

If I understood the Sm, I thought I should measure both ends of the em. resistors.

Yeah, apologies from me, it was not a great explaination.

We are trying to work out why the relay randomly releases. One possible cause is a spike in dc voltage. If you look at the sm and dc offset adjustment they ask you to check for 0V at Ro and Lo. Looking at the schematic, you will see that Ro and Lo are after the relay, so all good if the relay is engauged. But if the relay randomly releases then Ro and Lo are no longer connected to the power amps. So working back from the relay you will see a connection at the emitter resistors. So monitor the voltage to GND at this point, xxmV is not unreasonable, looking for a drift or spike into the hundreds of mV. If you are able to "provoke" the fault then that would speed things up.