[gnlsn]

Mine sdoes the same thing. Just tryed standing it on left side and it stayed on. Layed it down like it is supposed to be and it shut off in less then one minute. Back on left side and stayed working. Have tryed everything I can think of to figure out why it shuts off but nothing yet. Has to be a solder joint or wire doing this.

[irobot]

Thanks again for the reply.

Well, I solved part of the problem. No wonder I was measuring about 1.5V between the two ground systems. They are in fact electrically connected thru speaker terminal board. Oops, my mistake.

So now, the thing powers up, stays on, and isnt flakey. Except - no display!

VP voltages (-29V) are good, filament voltage is good, voltages around the display driver IC and fl displayare good. /FLR sig is good, CE on display chip is good.

Any ideas?

Thanks!

[Guest]

The roll off caps are !00mfd in this unit
This would give you offset if they are bad but in most cases you should still be able to keep the receiver on in the diagnostic mode. One other thing I would check would be the power supplies to see if any of the supplies have excessive ripple. Also check the backup cap (c-103) for leakage on to the pcb and trace damage.
Bottom line, it maybe the micro.
Good Luck.

[irobot]

One more question I forgot to ask -

You mentioned "roll off" caps. I presume you mean in the driver and output circuitry? I see caps in this area with values from 100pf to around .1uf

[irobot]

Also -

I carefully inspected every pin on the CPU under 5X magnification, and also thoroughly cleaned flux and other residue from on and near the chip itself.

[irobot]

Hi

Thanks for the replies.

By the way, even with the power (standby) relay bypassed, it still shuts down (display turns off, PRY signal goes low, although PRI, PRD and PRV seem alright). I take measurements for the CPU board using the MCONG ground bus. I presume this is supposed to be isolated from the E and DG ground.

Yes, I am aware of the grounding schemes Yamaha uses. So that's the first thing I check.

I have re-soldered practically every pad on the main 1 and 2 boards (which included the biasing circuitry), input (CPU), display, and volume control boards.

Voltages on the driver and outputs on the main 1 and 2 boards are all good.

I had pulled and inspected every board for loose wire and other FOD, and cleaned those areas used as ground points on the chassis.

Still confused,
Mike

[Drdave]

As Vetec said check all ground connection.The back panel plays a big roll in grounding in most of the Yamaha units. Check for DC offset,If you have it on any of the channels replace the roll-off caps.Solder connections on the bias transistors are also know to cause trouble.One other thing, look for wire strands from striped speaker wires that have fallen into the receiver and landed on the PCB's.
Good Luck.

[vtech]

Is it shutting off in Diag mode too?
You know that in Diag mode, you are essentially bypassing all protection so in other words, it must NOT shutdown while in diag mode(forced ON)
If not shutting down in diag mode, the alternating PS & DC could be anything from a bad connection/ground like maybe a hairline crack &/or solder splash somewhere on a pcb OR may be a buckling supply line.
Are you setup as a Yamaha servicer?

[irobot]

I already purchsed the schematic from Just Manuals.

Displays PS PRT and DC PRT alternately in diagnostic mode.

Voltages throughout unit are normal, including CPU.

[Justmanuals]

This Parts & Service manual can now be purchased for $10.77 and downloaded immediately after payment from http://www.justmanuals.com


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