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Yamaha RX-V795, R-V1105
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irobot



Joined: 13 Mar 2009
Posts: 45

PostPosted: Wed Jul 22, 2009 6:32 am    Post subject: Yamaha RX-V795, R-V1105 Reply with quote

Hi All,

Does anybody have any repair experience with the Yamaha RX-V795? (same as R-V1105)

This one has me perplexed. Seems these all have common symptoms from what I found on the net.

This thing behaves erratic. Powers up, but seldom does it stay on long enough for the speaker relays close. At the times when it does stay on, all it takes is to touch the thing and it powers off.

Most every voltage, solder connection, cable, connector, signal pin, has been checked and rechecked.

I tried everything to bypass the protection signals PRD PRV PRI without success.



Thanks,
Mike
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vtech



Joined: 08 May 2006
Posts: 1224
Location: USA

PostPosted: Thu Jul 23, 2009 4:16 am    Post subject: Reply with quote

Been a while since I have seen a Yama

Do you have the svc manual?
Any protection code in diag mode?
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Justmanuals



Joined: 21 Aug 2004
Posts: 1950

PostPosted: Thu Jul 23, 2009 5:21 am    Post subject: Reply with quote

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


Paul@justmanuals.com
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irobot



Joined: 13 Mar 2009
Posts: 45

PostPosted: Thu Jul 23, 2009 11:02 am    Post subject: Reply with quote

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.
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vtech



Joined: 08 May 2006
Posts: 1224
Location: USA

PostPosted: Thu Jul 23, 2009 5:32 pm    Post subject: Reply with quote

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?
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Drdave



Joined: 11 Jun 2009
Posts: 24
Location: South Florida

PostPosted: Fri Jul 24, 2009 1:15 pm    Post subject: Yamaha RX-V795 Reply with quote

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.
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irobot



Joined: 13 Mar 2009
Posts: 45

PostPosted: Fri Jul 24, 2009 8:29 pm    Post subject: Reply with quote

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
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irobot



Joined: 13 Mar 2009
Posts: 45

PostPosted: Fri Jul 24, 2009 8:32 pm    Post subject: Reply with quote

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.
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irobot



Joined: 13 Mar 2009
Posts: 45

PostPosted: Fri Jul 24, 2009 8:45 pm    Post subject: Reply with quote

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
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Guest






PostPosted: Mon Jul 27, 2009 8:41 pm    Post subject: Reply with quote

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.
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