Yamaha RX-V483 - No power (Transformer?) - Page 1
Forum section: electronics / repair

author: dammert89
author_rank: Contributor
timestamp: July 16, 2020, 11:32:28 am
content: Good day EveryoneI came across this site looking for a solution for my Yamaha RX-V483. I picked it up for R250 ($15) from a guy who said it is completely dead.After a bit of initial troubleshooting I think I found the issue. I have traced the tracks and it seems as if my sub transformer (T5401) is dead as I am getting voltage in but absolutely nothing out (See the yellow arrow). I found the part number in the service manual as well, but I cannot find any datasheet on the part (YJ212A00).https://ibb.co/smwrbCsCan anyone help me regarding this? Hopefully that is the only issue. If anyone needs any specifics that you want me to test let me know.PS. AC input is SA - 230V 50Hz.Thanks

author: Haenk
author_rank: Super Contributor
timestamp: July 16, 2020, 01:23:54 pm
content: These transformers are custom made (though might be found in another model from the same era and make) - they are not off-the-shelf parts. You could check continuity on the disconnected / unsoldered transformer, it might have blown a fuse in there. In simpler transformers, this might be fixable, but would be pure luck, if just the outer winding is damaged on a multi-winding transformer.So I fear this is not a easy fix, unless the transformer gets replaced (after checking all the stuff beyond it, that might have caused a short).

author: mzacharias
author_rank: Frequent Contributor
timestamp: July 16, 2020, 03:23:52 pm
content: More likely the switch IC on the primary side.Have you checked the transformer primary for continuity (ohms check)?By the way, one could sub in the secondary 5.6 volts easily enough for test purposes.

author: mzacharias
author_rank: Frequent Contributor
timestamp: July 16, 2020, 03:24:57 pm
content: Quote from: Haenk on July 16, 2020, 01:23:54 pmIt is a switch-mode transformer also, so right, not an off the shelf type.

author: dammert89
author_rank: Contributor
timestamp: July 16, 2020, 04:24:17 pm
content: Hi guysSo tested continuity on the transformer after removing it. Everything seems in order, there is continuity everywhere where there should be. When you refer to the switch IC are talking about IC541 (STR3A453)?

author: dammert89
author_rank: Contributor
timestamp: July 16, 2020, 04:45:41 pm
content: So tested some more voltages (on primary side.) got 1.9V on IC541, 1.055 on IC542 and 84mV on IC543. I see IC543 should be 2.928V

author: dammert89
author_rank: Contributor
timestamp: July 17, 2020, 03:16:49 pm
content: Hi there.So tested Diodes on underside of board and it looks like D5414 and D5403 are both shorted. Voltage drop is roughly .45 both directions on both. Waiting for the parts now. I ordered most of the parts today not the smd parts though. Only parts I cannot find are the switching IC IC541 and D5409.Anything I should have a look at? It seems these 2 Diodes are my issue. I havent tested any caps yet but if the Diodes don't work I will replace all the caps too.Thanks

author: mzacharias
author_rank: Frequent Contributor
timestamp: July 17, 2020, 06:28:42 pm
content: Good job finding those diodes. They may be pretty special so do try to replace with original types.When you say you measured 1.9 volts on IC541, you should have been (carefully!) using the negative side C5419 as your reference.

author: dammert89
author_rank: Contributor
timestamp: July 24, 2020, 05:18:02 pm
content: Sorry for the delay... shipping in SA is pathetic. Got everything up and running now. Switched out those diodes and I get my 5.5v. Unfortunately it was not just that. There is a second connector. +3.3M, DGND, ACPWR_DET, PRY and TEST. Can someone please explain what those pins are for? I am not getting the +3.3M. Any way to test everything now that I got my 5.5V back up. I assume PRY is to switch the big transformers relay(easy bypass), ACPWR_DET is also just 3.3V generated from the power supply I assume? Digital ground (just ground to chassis?) and Test?

author: elecdonia
author_rank: Frequent Contributor
timestamp: July 24, 2020, 07:08:25 pm
content: I'm very familiar with a similar Yamaha AV receiver model, the RX-V673. The information I'm providing below is based only on my work with the RX-V673. The RX-V483 may be slightly different.The switching power supply in the RX-V673 has only one output: 5.5V. It is capable of providing up to 5A of output current. This is a total of about 25W. There are several secondary voltage regulators, mostly located on the digital/HDMI PC board, which convert from 5.5V to a variety of other rail voltages used by the HDMI and the digital processing IC chips for both video and audio.The 5.5V output voltage should be present at all times while the unit is receiving AC power, regardless of the main on/off status. Power to the large iron-core transformer (bolted to the main chassis) is supplied only when the relay closes."+3.3M" is the 3.3V rail for the "standby" mode. In the RX-V673 this +3.3M rail is regulated by IC85, a tiny SOT23 packaged linear regulator located on the digital processing PC board. This provides power to IC83, the system controller MCU, which is also located on the digital processing PC board. This MCU controls every function and feature of the unit, including the response to pressing buttons on the front panel and responding to IR signals received from the remote control.As you observed, the +3.3M appears on a connector that goes to the switching power supply PC board. However, the +3.3M comes from IC85, so you will only see it if all of the PC boards are installed and connected to each other. In other words, the +3.3M does NOT originate directly from the switching power supply PC board itself.I have one "totally dead" and unresponsive RX-V673 unit where both IC83 and IC85 get "warm to the touch" after a few minutes. The switching power supply is working and is producing the expected 5.5V output. However, the +3.3M rail measures only about 2V. I suspect that something damaged IC83, the MCU, and that the 5.5V to 3.3V linear regulator (IC85) is entering its "current limited" overload mode rather than failing violently.I have two other RX-V673 units which are (now) in working condition. When in the "standby mode" neither IC83 or IC85 get warmer than room temperature.The faults in my other RX-V673 units were corrected by a proper "factory diagnostic and service menu" reset of the internal protection system. One of my RX-V673 units required a special procedure to "enter the correct model number into the EEPROM" located on the digital processing PC board. Look up "Yamaha AV receiver internal error fix" on YouTube to find the procedure for correcting "no model number" and/or "system error." This procedure is NOT documented in the official Yamaha service manual. I don't know where the YouTube person learned it, but I tried it and it works perfectly. I suspect this "model number" procedure was documented only in the "service bulletins" which are sent to authorized Yamaha repair centers.I'll soon be posting details of my ongoing project to fix several Yamaha RX-V673 units. I got started on this because my son has owned an RX-V673 for more than 5 years. It suddenly went totally dead 3 weeks ago. This is the unit where I suspect IC83, system controller MCU, has failed. I bought two "for parts or repair only" RX-V673 units (cheap) on ebay to get a fully functional digital PC board, which I then intended to transplant into my son's receiver. But then i found these "parts or repair" units had no hardware faults at all. They required only the "overload reset" and/or the "model number" restoration procedures to get them working again.

author: dammert89
author_rank: Contributor
timestamp: July 26, 2020, 11:02:45 am
content: Hi. Thanks for all the info helped quite a bit. So I found the 2 linear regulators for the 5.5v to 3.3v (3.3M and 3.3S) and there you go, both are outputting nothing. 5.5v is fine on the input though.Now to see if I can find replacement parts for that.You think I can use my 3.3v bench supply to bypass those ICs? For testing.

author: elecdonia
author_rank: Frequent Contributor
timestamp: July 29, 2020, 08:57:19 pm
content: Quote from: dammert89 on July 26, 2020, 11:02:45 am3.3M should be active at all times when the 5.5V input is present.The other 3.3V rail, 3.3S, should be 0V until the receiver actually switches on.I suggest diagnosing why there is no 3.3M. These tiny linear voltage regulator devices are fairly common and cheap. If you are lucky the fault is with the voltage regulator IC rather than with the MCU chip. The linear regulator IC chips for both 3.3M and 3.3S should be physically located on the digital PC board, not far from the MCU chip. Both linear regulators are in tiny SOT-23 packages with 5 pins.Hopefully someone will soon post schematics for these newer Yahama AV receivers. I believe the 2nd digit in the Yamaha model number often indicates the vintage. An RX-Vx7x is somewhat older than an RX-Vx8x. The first digit appears to represent the total number of audio channels. RX-V4xx for 5.1-channel, RX-V6xx for 7.1-channel.I haven't yet tried a bench power supply for my 3.3M rail yet. I will do that before long. I'll limit the current from my bench power supply to perhaps 50 or 100mA until I determine what is causing the excessive load on 3.3M-E

author: dammert89
author_rank: Contributor
timestamp: August 02, 2020, 03:27:16 pm
content: Thanks for the feedback. Yes. 3.3S CE feeds off the 3.3v of 3.3M. I cannot find the same linear regulators here in SA though. But I was thinking of soldering some single headers to the through hole test points and testing another generic 3.3 regulator that has a chip enable (similar amps) . I actually have the service manual for this board(if it wasn't for that I would never have figured this out). I picked up how they do their version numbers. I have an older 377 as well where I think the STK has gone.

author: dammert89
author_rank: Contributor
timestamp: August 11, 2020, 07:21:02 am
content: Hey Everyone. Just an update, So I replaced both the 3.3v regulators with similar regulators I had laying around. So far so good. Been using the receiver for about a week now with no issues.I actually went out and got myself another dead receiver to see if I can bring it back to life. (RX-V475)Will start a new thread on that one.Thanks again for everyones input.

author: dbgeek
author_rank: Newbie
timestamp: January 17, 2025, 03:38:16 am
content: I have a similar issue with RX-V579,where I do get 3.3 M from board to standby power supply,but receiver does not run on,Jumoing relay on standby makes a clicking sound on main amp board but unit does not come on any idea if regulator or some other part may be faultyThanks