Yamaha RX-V357 amplifier, no display, no diag mode-only power relay toggle - Page 1
Forum section: electronics / repair

author: xavlaur
author_rank: Contributor
timestamp: December 29, 2020, 10:00:00 pm
content: I have an Yamaha RX-V357 that suddenly stopped working , no protection mode , no display , no diag mode - only power relay toggle (clicking on and off). I've already disconnected power stage voltages in order to avoid any output / speaker DC protection and also power relay is by-passed in order to have all voltages ready-to-be-checked from power transformer. Almost all voltages seem to be correct, except 5MS that missing. If 5MS externally provided no more relay clicking but still no display. Any help ?

author: xavlaur
author_rank: Contributor
timestamp: January 02, 2021, 05:48:30 pm
content: 1.DC:37% PS:16%2.THM: 490% 5 FAN4.IMP:6 PL:255%

author: xavlaur
author_rank: Contributor
timestamp: January 02, 2021, 06:23:59 pm
content: There is any control of DC output voltage by pre +BV / pre -BV voltages on STK 403-130Y ?PS:16% is referenced by main +/- B, pre +/- BV or any other critical voltage alongside diagrams ?...In service manual is no range for PS, DC etc how can I find within limits is normal ?

author: m k
author_rank: Super Contributor
timestamp: January 03, 2021, 05:12:03 pm
content: Quote from: xavlaur on December 29, 2020, 10:00:00 pmS12 must also have its 13V, source(red 1) for PDET, power detected perhaps.Then that diode triplet a bit left of Q244, they also must have their voltages.Vertical one is 5BU, that is Vcc and AVcc for MCU.Then Q259 must release RESET(red 2), that seems to be active low.

author: xavlaur
author_rank: Contributor
timestamp: January 03, 2021, 06:02:00 pm
content: Thanks a lot, I've studied this diagram that I began dreaming it ... Still I'm concerned of:a) how can I control DC offset of STK 403b) PS PRT - wich is normal range for it, wich is IC 242 pin for it ?as you can see 5MS repaired and now I have display and diag mode... but still 3 errors...DC:37% -I don't know how to control DC offset of STK 403, it is 1 V in my casePS:16%-I don't know how to solve- all voltages seems to be okTHM: 490% 5 FAN-I know how to solveIMP:6 PL:255%-I know how to solve

author: xavlaur
author_rank: Contributor
timestamp: January 04, 2021, 11:36:05 am
content: Helo,guys ! Thks for your support. Finally ... it's working... I'll tell you the whole story.1. Power relay click-on-click-off solved by LM7812 on S12 output. S12 now is 12 V sharp instead of 13V. My power module - factory made - was without any stabiliser transistor. None. Nil.2. Display off solved by replacing Q244 in order to have 5MS3. Now I have display & DIAG MODE. Found all STK with DC on output. STK 403 had 1 V DC offset. STK 404 had 49V DC offset.STK 403 DC offset corrected by double-grounded the rear panel !!! Seemed that one crocodile clip was not enough ! As a conclusion, DC offset do not depends on main power supply , nor pre - power supply due it is an AB class topology and it is affected only by it's inputs. On the other hand it is normal to be so due LIMB (pin 4 of IC 242) affect pre +BV power supply on STK 403 and the result is not a DC offest but a power control.STK 404 DC offset still in study, I have a feeling it'n not burned.STK 404 not on board anymore.4.DC:37% PS:16% protection becames DC:27% PS:16% - after double grounding the rear panel and seems to be NORMAL STATE due no more "protect mode"5.THM: 490% 5 FAN becames THM: 0% 5 FAN after grounded pin 1 of STK 404 (that is no more onboard)6.IMP:6 PL:255% seems to be NORMAL STATE due no "protection mode" on start and also clear audio power signal on output, not limited. Also 4 P93 LIMB O Power Limiter Control now is 0V on pin 4 of IC 242, that is normal a/p manual.I'll came back to you if STK 404 was affected by wrong grounding - like STK 403 cases, altough DC +49V on output seems to be out of order.