Yamaha CA-810 Relay Randomly Engages

[AngelAT]

Hello fellow AKs,

I got a CA-810 and working on such a unit for the first time.
When she came the relay was not engaging, but when tapping on the Power board it would engage. Easy fix - came out there were some cracked solder joints on some of the transistors. Re-soldered the whole Main amp CB and I thought this fixed the problem.
Next I replaced (almost) all electr. capacitors and re-lamped the unit. Set the 20mV and checked Lo and Ro. They are ca. 9 mV and 19mV resp.
I thought this is acceptable and I can enjoy the nice sound if the Yamaha.
BUT, the relay started engaging randomly - sometimes after one hour once, sometimes more often for a few times in a row.
What I did is replaced all transistors from the protection circuit - TR601 to TR606 but this did not fix the problem.
I have checked all driver and output transistors and they measure OK.

Has any of you, guys, had such a problem and managed to find a solution?
Any ideas are welcome!
Thanks!

 

[Nashou66]

A couple things.

• Check any fusible resisters on the drive or amp board and the protection circuit , they can sometimes drift high.
• did you clean all the control switches very well, sometimes just spraying cleaner in them is not enough and they require dismantling to clean them well.
• check again for any code solder joints on the drive/amp board

Athanasios

 

[AngelAT]

Thanks, Athanasios for the prompt reply!

Yes, I thoroughly cleaned all pots and switches - also checked and when I use them, the relay seems not to to be influenced by them. This makes me think that they are not causing the issue.
Checked several times for cold SJs and could not find any - also when tapping the boards with a screwdriver does not seem to change the behaviour of the relay.
But I will check the FRs. Have you experienced such a behaviour from them - causing intermittent connectivity? I have once worked on a Yamaha receiver but there they were just blown.

Cheers,
Angel

 

[Sparkplug]

Have you inspected/cleaned/changed the relay itself?

 

[AngelAT]

Have you inspected/cleaned/changed the relay itself?

TBH, none of the above. So far I have never seen ( experience is just a few years) a relay causing such problems. The only issues I have had with relays in this respect were problems with the sound passing through due to bad contacts. All others were caused by circuitry components.
Do you think the relay might be defect, causing such strange behaviour - in and out every now and then? I was thinking more for a transistor, or sth similar...
But, again, my experience is limited, so I will check the relay itself.
Thanks for the idea!

 

[Sparkplug]

I’d change the relay and be done with it, it’s certainly time. Is it HC-2 24V? Can’t remember …
Please stop changing parts until you have a better idea of what the root cause may be. Every random change introduces more chance for further imbalance and instability. You can resume changing parts after this issue is resolved and if there’s a need to do so.

As was stated above, the root cause is most likely in bad/poor connections, cold solder joints, cracks in traces (hard to find) corroded connectors, poor RCA connector solder joints (most don’t check this) among other physical problems.

 

[AngelAT]

I fully agree with you about the causes!
That's the reason I reflowed the main power amp board and the connections between the boards (I have not reflowed the preamp board, though). Tightened the ground screws. Checked RCA connectors - no cracks there. Usually when there is a cold SG and I tap the board there is a change - now nothing...
BTW, this relay is obsolete. Do you have an idea what I can use as a replacement?

 

[Sparkplug]

I fully agree with you about the causes!
That's the reason I reflowed the main power amp board and the connections between the boards (I have not reflowed the preamp board, though). Tightened the ground screws. Checked RCA connectors - no cracks there. Usually when there is a cold SG and I tap the board there is a change - now nothing...
BTW, this relay is obsolete. Do you have an idea what I can use as a replacement?

Here it is:
https://www.mouser.com/ProductDetail/Omron-Automation-and-Safety/MY2-02-DC24?qs=sGAEpiMZZMtSzCF3XBhmW7nRSRDOvRrS5erS6Kjjho4=

Please reflow the rest of the solder joints as well, it’ll save trouble down the road and ‘might’ even solve your problem, the same goes for RCA connectors, even if they look good .

 

[AngelAT]

Thank you for the link!
I will do as advised and then will report the results!
Cheers!

 

[AngelAT]

Bad news!
Did all that you guys advised and got the same result...
Reflowed the rest of the boards (including the chinch connector board), new relay, a few bi-polar caps which I did not have initially and I still have the same problem. Relay engages randomly - sometimes a few times in a row, sometimes just once. Every now and then...
Any other ideas?
@Patrice, @avionic? Anyone else?
Could it be that the drivers or the outputs randomly get bad for a few seconds?

 

[mbz]

Possible causes include intermittent dc offset so the relay responds, this offset caused by faulty components in power amp. Another possibility is sagging power supply to relay coil, psu dips a little and relay releases. Also possible failure in protect circuit however all caps/transistors replaced so unlikely.

Suggest monitor the dc offset at Ri, Li(don't have schematic?) or between emitter resistors. is offset relatively stable or does it drift into the 100's of mV? Also monitor the 12v/24V(?) at the relay coil, is this reasonably stable or does it dip... You will need to have the MM connected for 10-30min(?) and observe changes as things warm up, would be great if you could capture the measurements while the relay is toggling.

 

[Nashou66]

I had an issue on my A-1 where it do the same thing as it warmed up. Turned out that the voltage regulator for the relay power wasn't screwed tight to the heat sink and after removal the thermal paste was also dry as a desert .
Removed it cleaned the part and heat sink, replaced the grease and its been fine since. I think it over heat and loose the proper voltage. might be the same issue.

nashou

 

[AngelAT]

I had an issue on my A-1 where it do the same thing as it warmed up. Turned out that the voltage regulator for the relay power wasn't screwed tight to the heat sink and after removal the thermal paste was also dry as a desert .
Removed it cleaned the part and heat sink, replaced the grease and its been fine since. I think it over heat and loose the proper voltage. might be the same issue.

nashou

Thanks, Nashou!
I reworked all transistors - new thermal paste, resoldering, all...
I will now do as mbz suggested. I tried it once but just then the relay was not engaging so I gave up. I will now just wait and observe what is happening.
Will report results

 

[AngelAT]

OK, an update
Checked the idle current at the two emitter transistors and the relay voltage at the coil.
All seems OK as I see it.
Check 1:

Check 2:

As I see it, voltages at the transistors stay stable at ca. 17-19 mV. The voltage at the coil of the relay stays ca. 24V. At the start of the amp, the voltage at the relay went up to 24.7V, but that is the highest and then all looked OK.
I believe this is not helping me...

 

[AngelAT]

One more thing: I saw that the board was a bit bent at one end - where the left channel is. Comes out the board is cracked, but looking at it, it seems like it is not affecting any traces.
Just removed the screw which is close to the traf and then pressure is released.
But the problem is still present.
Continue investing

 

[Sparkplug]

One more thing: I saw that the board was a bit bent at one end - where the left channel is. Comes out the board is cracked, but looking at it, it seems like it is not affecting any traces.
Just removed the screw which is close to the traf and then pressure is released.
But the problem is still present.
Continue investing

Your problem has nothing to do with semiconductors and everything to do with solder/trace cracks somewhere in my opinion, your descriptions are dead giveaways. Trace cracks are very difficult to locate as they look fine on the surface. I would try to induce the problem by applying mild pressure to different parts of the board and trying to narrow down the area it’s coming from. Takes patience …

 

[AngelAT]

What you say makes sense.
Pushing, tapping, so far nothing...

 

[Sparkplug]

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

 

[zaibatsu]

Possible causes include intermittent dc offset so the relay responds, this offset caused by faulty components in power amp.
...
Suggest monitor the dc offset at Ri, Li(don't have schematic?) or between emitter resistors.
...
would be great if you could capture the measurements while the relay is toggling.

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.

So far I have never seen a relay causing such problems. The only issues I have had with relays in this respect were problems with the sound passing through due to bad contacts. All others were caused by circuitry components.

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

 

[mbz]

our problem has nothing to do with semiconductors and everything to do with solder/trace cracks somewhere in my opinion

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.