Yamaha RX-A2020 delayed audio at power on

5

59ctd

Audiophyte
#1
I've had this Yamaha RX-A2020 for a few years now - purchased new from BB. I have not used it myself much for the past 2 years since my teenage son has taken over the basement as his appt. He has used it every day and night for quite a while now. Lately when powering it on it takes a long time for the audio to kick in. Does not seem to matter which audio/video source is selected and the time seems somewhat random from a few minutes sometimes to several hours other times. Any ideas? Is it worth getting repaired or trying to tackle myself? I am fairly versed with electronics and repair but am unsure where to even start with a diagnosis.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,381 17 25
#2
I've had this Yamaha RX-A2020 for a few years now - purchased new from BB. I have not used it myself much for the past 2 years since my teenage son has taken over the basement as his appt. He has used it every day and night for quite a while now. Lately when powering it on it takes a long time for the audio to kick in. Does not seem to matter which audio/video source is selected and the time seems somewhat random from a few minutes sometimes to several hours other times. Any ideas? Is it worth getting repaired or trying to tackle myself? I am fairly versed with electronics and repair but am unsure where to even start with a diagnosis.
The problem is going to be with the timer circuit to the speaker relays. A lot of amps, if not mos, send out a thump to the speakers on turn on. This can be damaging to the speakers. So the output from the power amps goes to a relay that has a timed delay, to close the speaker relays after the turn on thump.

This relay is usually controlled by the ubiquitous LM 55 timer circuit. The LM 555 is an common IC for this purpose from Texas instruments.

For this purpose the timer is usually set up in monostable mode.

This is a typical circuit.



Now the time is set by the ration of C1 and RV 1. The timing of the circuit is usually set by calculating the correct value of RV1 and using a fixed resistor. Now C1 also affects the timing, and the most common reason for the problems you are encountering is failure of C1. The IC itself could also be at fault.

Now your problem is going to be finding this little IC circuit in a cluttered unit like a receiver. What makes it really difficult is that manufacturers rarely publish circuits and or service manuals. You might be able to trace the circuit back from the relays. It will be in the circuit that sends the power to activate the relays in the speaker output circuits.

First check that the value of the cap is correct. If so check resistor values. If these values are correct them the LM timer chip needs replacing. They cost 80 cents each. Good luck. Odds are heavily on the cap being the problem.
 
5

59ctd

Audiophyte
#3
Ah the old LM555 timer IC. I remember working with those back in high school in the early 80s. I too was thinking about the issue likely being a capacitor that is bad. My wife's Samsung TV has a bad cap that prevents power-on sometimes. Is this capacitor likely to be exactly 1000uF or just around that value? One thought was to open it up and see if there are any caps that look swollen at the top end. I found another post with a similar issue with an RX-A2000 and someone recommended looking for bad caps in the power supply. Unfortunately there was no response or resolution there.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,381 17 25
#4
Ah the old LM555 timer IC. I remember working with those back in high school in the early 80s. I too was thinking about the issue likely being a capacitor that is bad. My wife's Samsung TV has a bad cap that prevents power-on sometimes. Is this capacitor likely to be exactly 1000uF or just around that value? One thought was to open it up and see if there are any caps that look swollen at the top end. I found another post with a similar issue with an RX-A2000 and someone recommended looking for bad caps in the power supply. Unfortunately there was no response or resolution there.
I don't know what the value of the cap will be. The time out is set by the RC ratio. The circuit could well be on the power supp;y board. The cap is low voltage and will be small. It is highly improbable that the cap will have any physical evidence of failure.

If you can not locate the timer circuit then you are out of luck. You have to find that chip circuit or you will be SOL. I have not done a search for a circuit or service manual of that unit, but you should. You sometimes get lucky with older receivers.

It is very hard to service anything that complex without a circuit and preferably also a service manual, then you can see where the parts you are looking for are located.
 
S

snakeeyes

Audioholic Field Marshall
Ratings
846 1 1
#5
What conditions cause this type of failure? Too much dust? Bursts of power?
 
M Code

M Code

Audioholic General
Ratings
557 1
#7
Firstly...
I would check the contacts on the subject power relay..
After so many years of ON/OFF use the contacts can/will create pits making poor, intermittent contact...

Just my $0.02... ;)
 
5

59ctd

Audiophyte
#8
Firstly...
I would check the contacts on the subject power relay..
After so many years of ON/OFF use the contacts can/will create pits making poor, intermittent contact...

Just my $0.02... ;)
That should be easy enough to locate and verify good power passing through there. The unit appears to power up normally but the speaker relay is what is delayed.
 
5

59ctd

Audiophyte
#9
Trying to locate the service manual with schematics is proving to be difficult for the RX-A2020. I found the service manual for the RX-A3020 but I am unsure if that might be even close to the same internals. I've located a few non-Yamaha sites that claim to have the service manual for a $10 or $16.99 fee but I am leery of doing business with an unknown entity when I have no idea what their product consists of. I also found a usa.yamaha.com page telling me what item# format to use for a service manual for this unit (S M RXA2020) but have not figured out how to order the item from them yet.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,381 17 25
#10
Firstly...
I would check the contacts on the subject power relay..
After so many years of ON/OFF use the contacts can/will create pits making poor, intermittent contact...

Just my $0.02... ;)
That would be very unlikely, as you would have to postulate that all contacts to all the speakers failed at once and continue to lose and make contact at the same time. Honestly an impossible proposition as when the unit has no sound there is no sound from anywhere. So I stand by the proposition that this is most likely a failure in the timer/delay circuit.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,381 17 25
#11
Trying to locate the service manual with schematics is proving to be difficult for the RX-A2020. I found the service manual for the RX-A3020 but I am unsure if that might be even close to the same internals. I've located a few non-Yamaha sites that claim to have the service manual for a $10 or $16.99 fee but I am leery of doing business with an unknown entity when I have no idea what their product consists of. I also found a usa.yamaha.com page telling me what item# format to use for a service manual for this unit (S M RXA2020) but have not figured out how to order the item from them yet.
Give them a call and see if they will make a service manual available to you. Usually they only make them available to certified service centers. That also leaves the independent repair guys out in the cold. That is why they are on the endangered species list.

I have long been of the view that access to the circuit and a decent service manual should be available to all owners by law, and all qualified service techs. Firms use to do this. Back in the day Quad used to include all circuits in every user manual, but not now our Chinese masters have the whip hand.
 
5

59ctd

Audiophyte
#12
I called Yamaha's toll free number and they were happy to send out a service manual on CD for me. Only $25 for the CD and shipping and it is on the way. They said they burn them to CD when there is an order instead of having tons of CDs stashed away in a warehouse.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,381 17 25
#13
I called Yamaha's toll free number and they were happy to send out a service manual on CD for me. Only $25 for the CD and shipping and it is on the way. They said they burn them to CD when there is an order instead of having tons of CDs stashed away in a warehouse.
That will make life a lot easier for you.
 

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