Yamaha RX-V657 protection circuit problem help? Solved - Page 1
Forum section: electronics / repair

author: xenocatalyst
author_rank: Newbie
timestamp: January 24, 2022, 01:59:38 am
content: Hi All, This is my first time posting here. I have posted this elsewhere but thought I'd try here as well.I've recently been given a receiver with no history.I'd like to use it as I have not had a good sound system for a long time (read as I got married and had kids).Although it is old this Yamaha looks and feels like a good quality unit.But,.... it doesn't work.It will start up for 1 second or 2, the display lights up and then it shuts down.I have looked everywhere for info regarding this, downloaded the service manual, and it looks like the power supply is out of spec and potentially the temperature sensor could be blown.When booted into diagnostic mode it shows a code, DC:007 PS:034.According to the manual DC:007 is in range but the PS:034 out of the 36 to is low and triggers the protection circuit.The problem is, I really don't know what that means or how to resolve it.Other thing I found was THM:000. Now this is supposed to be between 9 and 167/177 (depending on region)This may indicate that the temp sensor is stuffed, or that the low voltage is preventing it from reporting properly giving my a 000.But I'll concentrate on the power supply first.image below is form manualIs there anyone who could point me in the right direction or help me troubleshoot the problem?I'm not afraid to pull it apart and I'm pretty handy with a soldering iron.Thanks, Roy.

author: bob91343
author_rank: Super Contributor
timestamp: January 24, 2022, 07:51:00 pm
content: First, locate the temperature sensor(s). They will either be thermistors or switches. Measure them to see if they are working properly. If necessary, open or jumper as required to see if the error message changes.

author: PKTKS
author_rank: Super Contributor
timestamp: January 25, 2022, 12:27:10 pm
content: Yep you have go far enough ...So if I were you... once having it taken apart...I would not waste the work would replace the crappy regulator associated with the error code as well it would not be the first case these regulators fail short..Alas this is the most common problemPaul

author: xenocatalyst
author_rank: Newbie
timestamp: January 26, 2022, 05:02:13 am
content: I did a check on the sub trans voltages using the schematic from schematic as a reference. And I'm getting readings at the transformer that are way too high.I can't read enough electronics to understand what's happening.Any ideas?230vac instead of 152 and 13vac instead 7.5

author: ambrosia heart
author_rank: Regular Contributor
timestamp: January 26, 2022, 05:11:28 am
content: " And I'm getting readings at the transformer that are way too high. " I don‘t read the schematics. But previous experience told me marked voltage is 100V input. If your AC input is 220V, output voltage will be higher.

author: xenocatalyst
author_rank: Newbie
timestamp: January 26, 2022, 05:13:43 am
content: Here In Australia we have 240v

author: ambrosia heart
author_rank: Regular Contributor
timestamp: January 26, 2022, 05:50:20 am
content: Reply 3 schematics is standby board. 90% not related except +5M. You should check the followings.1.All regulators in HDMI board. From my memory, there are 2 regulators give 0V that are normal.2.ALL regulators in RCA board giving +/- 12V AND +/-5V as well as +B OR -B for power amp. Some need transistor regulation.3.Read service manual carefully. It tells you what voltages leads to such a protection, in somewhere pages4.Schematics parts at last pages , caps, resistors, ic, written電源 means regulstors. You should find them out and check input and output voltage.

author: xenocatalyst
author_rank: Newbie
timestamp: January 26, 2022, 07:00:29 am
content: Hi Ambrosia,Thanks for the insight.Part 1 is easy - no hdmi.I'll check the rca and amp as soon as I can find a little time.

author: xenocatalyst
author_rank: Newbie
timestamp: February 15, 2022, 11:44:35 pm
content: UPDATE:I've solved the issue.I decided to investigate the discrepancy with the temperature sensor. IC301I found that it was not receiving 5v it required to operate. It gets it power from IC304 a 5v Linear voltage regulator, LM7805.After replacing this regulator all is well. The receiver is now working again. And I'm very happy with it.Great for a $2 fix.