Yamaha RX-V795a Receiver doesnt power on

[Rick79]

I found a video on YouTube about the same model and symptom im having. The contacts on the same relay were dirty causing the receiver not to power up just like mine. So i opened the relay on mine and i cleaned the contacts. It turns on now, but it shuts off after 4 seconds every time i try it. When i power it on, the display has no warning message or anything like that, it just shows its in the FM stereo mode and then it turns off.
Im gonna buy a new relay, but i have a feeling there must be something else wrong in the receiver that is causing it to shut down.
Do you think its just the relay not making a good contact? I noticed on the board next to the relay it says "Short Relay" between two jumper wires. Is that for troubleshooting the relay im having problems with? If yes, do i just short it out with some alligator clips?

 

[shrtrnd]

Yeah, I checked your link. They want you to click on some 'sign up' selection. I'm not letting whoever is running the site into my computer.
Your symptom now seems to be that your receiver does power-up (for less than a second), and then immediately shuts down. And you mentioned it has switchable power outlets on the back of the receiver.
Do you have some circuit or module on the board or attached to the back of the chassis for the external power sockets?
My guess is that you have a short somewhere in the power supply or switching circuit, that is causing the receiver to protect itself, by shutting down.
If that's the case, your receiver circuitry may be alright, and you just have to track down the fault that is tripping your auto-protect circuitry.
I'll recheck your photos when I have time to see if I can find any specific area to take a look at.
I'd be specifically looking for anything that would short-out.
Some circuits have bleeder resistors to drain capacitors, some don't.
With the power off. Use something to short-out the two big electrolytic capacitors next to that relay to de-energize them. You'll get a spark if they have voltage on them, so don't be alarmed. I use something
with insulated handles so I don't get shocked. A needle-nose plier, or screwdriver. After discharging the capacitors, I'd use my ohmeter to check the caps, looking to see if one of them is shorted.
The ohmeter will start reading upscale (or downscale, depending on polarity), if the capacitor is good, and starts recharging itself from the battery in your ohmeter. If the ohmeter doesn't start reading an increasing or
decreasing resistance, the capacitor is bad, and would explain this symptom.

 

[Rick79]

Ok, im gonna have to take it all apart again to get to those capacitors so i'll post about that in a while.
Yeah, the receiver stays on now for about 3 to 4 seconds and then shuts off.
The external power sockets are attached on the same board. I dont see anything shorted and the plugs work when i turn on the receiver.

 

[Rick79]

That link i gave you where the service manual is, below it says "This file is downloadable free of charge: ... Processing"
You wait a few seconds for the word "processing" to change into the words "Get manual" and you then click on it and it starts downloading.
It lets you download 2 times without signing in. Ive download a service manual before from that site and i was able to read it, but for some reason i cant get my phone to download this yamaha manual. I may not have enough space on my phone.

 

[Rick79]

I was looking at the main speaker terminals that are soldered directly on to the main board. I noticed that the two screws that hold the speaker posts at the back or the receiver are actually grounded. Im guessing thats the ground for the main board because after i put those screws back in, the receiver now stays on and its working now.
I had left those screws off because how i had to be taking the main board out over and over. So it looks like the only problem was the bad relay and possibly because IC704 was loose.
I posted a photo of the screws that are grounded.

Even though its working now, im gonna replace the relay

 

[shrtrnd]

And you didn't even need a manual. You're getting all kinds of experience. Pretty soon you'll be suggesting help for other people asking questions on this site.