Help needed with Yamaha RX-V1600 receiver repair

[Dangerous]

Hi all. First post on here. From numerous Google search hits and the posts I’ve already read through, this looks like the place to go to find answers on Yamaha receiver faults. I have an older but good quality and otherwise good condition Yamaha RX-V1600 receiver that is doing the usual Yamaha “turn on for one second and turn off” trick. It’s not the usual 22nF capacitor on the power supply going low – that’s the first thing I tried. I’m pretty sure it’s also not an issue with the output stage being shorted or blown either. I can get it started and sitting idling OK in diagnostic mode, where it idles ok, consuming around 30 watts, which I presume is acceptable. I’ve taken all of the amp boards out to check if any output stage components are faulty (just a visual inspection and a junction and s/c check with a meter), but they all appear to be ok. All the Diagnostic Self Diagnosis functions appear within spec according to the service manual except 16 – Protection History, which comes up with “PS2 000” on every startup, indicating a fault with the power supply 2 board, or something feeding it. Given that it is “000”, I presume it thinks a voltage is missing, ie 0V.

I've accessed the service manual at https://www.manualslib.com/manual/1069965/Yamaha-Dsp-Ax1600.html?page=105#manual





(Here's a jpeg of the power supply 2 circuit diagrams - I hope that worked - if not, link is  https://ibb.co/G25cNqX )

My first question is regarding the voltages written in red on the PS2 circuit diagrams. I can’t see anywhere that it is stated if these are standby voltages (ie amp plugged in but off), or ON voltages, where the amp is fired up and operational. Also, if they are ON voltages, do they apply to normal operation as well as diagnostic mode operation? Can anyone clarify this?

I’m presuming that the unit has a power detection issue, which is the area that I’m looking for faults. That’s just a hunch at this stage from what I’ve read, learned and gleaned from the service manual. I might be heading in the wrong direction though.
The Power Detector circuit voltages from the PS2 board to the Function board are as follows – the first figures are the figures in red on the service manual circuit diagram, the second are measured voltages with the amp in standby mode, and the third are measured in diagnostic (on) mode. They are measured with an older digital multimeter, so allow a few % tolerance.
LFAN – 0/0/0  (seems ok, as fan should be off)
FAN - -0.5/0/0 (seems ok, as fan should be off)
S10 – 9.3/8.9 to 9.3 unsteady/8.72 unsteady (see note 1 below)
PRY – 0.6/0.001/4.66 (see note 2 below)
MG – 0/0/0 (ground)
PDET – 5.4/5.6/5.4 (I presume this is the signal back to the logic board so it can detect a fault??)
+5M – 5.4/5.82/5.80 (does this seem a little high, which would potentially result in a PDET signal that signifies a fault??)
RES – 4.9/5.08/4.88 (not sure what this signal does?)

Note 1 – S10 voltage – is this derived from the rather complicated primary PS2 circuit, with a transformer switched/chopped by transistor Q6 and bridge rectifier D10, with the secondary rectified by bridge D11 to supply the 9.3 volts DC? Just guessing here.

Note 2 – PRY – this is the signal that switches on the transistor that switches on the relay to provide mains power to the main transformer. It would make sense if this signal was low on standby and high on “ON”, which would mean the voltage levels in red on the circuit diagram were for standby mode, not ON mode?
I have taken out the PS2 circuit board and inspected it for cracked or dry solder joints, but I haven’t seen anything obvious.
I don’t have access to a CRO, so I can’t look at or diagnose any waveforms at the moment – it’s a home repair effort on the lounge table, using basic tools and multimeter. I’m at the stage where I’ve ordered a few components to replace on the PS2 board, but I’ll pretty much be guessing which ones may be the culprits if any, and resoldering anything that looks even remotely suspect while I'm at it. If anyone can give me any advice on what to look for or any specific component or any other circuit board that may be causing this fault based on the info above, I’d really appreciate it.

Thanks all, Dangerous.

[PKTKS]

This sounds like a typical semiconductor fault.

In fact the diagnostics helps but several times the
fault of such device may be far from the PSU itself

You should first eliminate the PSU from the equation.

Scopes won't help in such cases.

A proper method of turning the PSU itself with a DUMMY
LOAD (which you can control and load by yourself) will
help to exclude faults on the PSU itself.

Then you can move to next section in chain..
probably on those crappy transistors (more channels more stuff
even if only have 2 ears... go figure...) which you will need
to figure how to check

.. even with them  attached to those crammed heatsinks..

laborious things.
Paul

[mzacharias]

See if perhaps this pertains to your problem.

[Dangerous]

Thanks mzacharias for that info. It looks promising. I haven't got to that board yet. I still had the PS2 board out, so I've given it a thorough check over, and it seems OK except for a suspiciously low AC voltage out of the small transformer - it's meant to be 6.9V ac, but it's more like 4.5V. Maybe that's my old meter being confused by a complex voltage waveform if the transformer is being fed by a chopped voltage, as it looks like all that this AC voltage does is get rectified to 9.3V DC (S10), feed the main power relay (which pulls in ok), and then S10 goes off to the function board to a 5.8 volt regulator, and the function board sends this 5.8 volts back to the PS2 board as +5M, and +5M is sitting pretty close to 5.8 volts. It's a horribly complicated circuit for an on switch!

Once I am finished with PS2, I'll follow your suggestion, and let you know how I go.