Yamaha RX-A380 DC PRT 0L / Circuit Protection Problem (yet another...) - Page 1
Forum section: electronics / repair

author: slater0013
author_rank: Newbie
timestamp: May 27, 2023, 04:40:33 pm
content: Hello from FranceI have a Yamaha RX A830 audio/video amplifier ! Worked like a charm for years.And suddenly, impossible to turn it on, circuit protection turns it off immediatly.As mentionned in service manual, I went through the Diagnostic menu to see : DC PRT 0L (sometimes 2L 3L 4L)Using a Voltmeter, I can measure that the FRONT RIGHT speaker output is around 5V when all the other speaker outputs are measured around a few miliVolts.I guess I found the faulty channel, but what to do now ?https://cloud.univ-grenoble-alpes.fr/s/Xxgqozd3ZmFMppAI guess the 5V measured at the speaker output is what I would measure at R1150 ? I need to find the adequates probes to avoid shorting any other components.I do not really understand why I should cut the resistor and what It could help me with, I suppose the problem is somewhere else.https://cloud.univ-grenoble-alpes.fr/s/RaccmgyxSfZW2Pgandhttps://cloud.univ-grenoble-alpes.fr/s/gTejszGEGK4N2Qtshows the components related to FRONT LEFT and FRONT RIGHT channels.There are quite a few to try ! And if I can manage to test resistors and capacitors, how to test transistors properly ? What would you try first ?https://cloud.univ-grenoble-alpes.fr/s/bGRz59NanAd3MoaJust looking at the board, nothing seems to be explicitely dead !Any ideas ?Thanks,GS

author: slater0013
author_rank: Newbie
timestamp: May 27, 2023, 04:54:03 pm
content: Also uploaded physical implantations of the components on the mainboard:https://cloud.univ-grenoble-alpes.fr/s/fPSd7jQkSM6AqBJ

author: David_AVD
author_rank: Super Contributor
timestamp: May 29, 2023, 09:01:38 am
content: Was that 5V on the speaker output measured on the centre pin of the emitter resistor, or on the rear panel terminal?The reason I as is that if the speaker relays are not engaged due to a DC fault, you'll need to measure at the emitter resistors.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 29, 2023, 11:04:33 am
content: who said you had to cut a partyour amplifier at this level is not adjustable, you have electronic problem(s) you have to differenciate ..first you check supply lines and all the related voltages, for sure something is affecting the outputsare you equipped to do some tests, voltages tests, component tests normally when possible at zero volume you take CAREFULL MEASUREMENTS on the good channel at key points (voltages, in and out of each tansistor chain) around the biais transistor etc ....AND CROSSCHECK on the bad channel to see where it begun to drift, could be a simple as : a cold solder / bad connection .........

author: wasedadoc
author_rank: Super Contributor
timestamp: May 29, 2023, 12:03:53 pm
content: Quote from: slater0013 on May 27, 2023, 04:40:33 pmYes the problem is elsewhere. Cutting the resistor makes only a small adjustment. Cutting it will not cure the fault you have.

author: slater0013
author_rank: Newbie
timestamp: June 01, 2023, 06:55:18 pm
content: Hello,Yes I measured directly on the speaker output !GS

author: slater0013
author_rank: Newbie
timestamp: June 01, 2023, 07:05:54 pm
content: I just brang the amplifier at home, easier to make measurements.I managed to find probes !Will make more tests

author: slater0013
author_rank: Newbie
timestamp: September 13, 2023, 09:37:12 pm
content: Hello,A friend of mine took the amplifier for a while, cut, removed and tested the output transistors marked in green Q1052C and Q1052A. Working correctly, PNP and NPN. We tried to start the amplifier again without the transistors and still -5V at the speaker output, and circuit protection still triggers.https://cloud.univ-grenoble-alpes.fr/s/Q5iqYdjpmEASZqqMy guess is that the first stage of amplification might be faulty (labelled Q1038 and Q1045 if I get It right) ? Would you identify other usual suspects ?Thanks,GS