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Electronics => Repair => Topic started by: Kentakung1 on January 08, 2020, 05:37:07 pm

Title: Yamaha rx775
Post by: Kentakung1 on January 08, 2020, 05:37:07 pm

How to fix.


Error. Code. Protect. Dc prt 75h


Help me. Please

Title: Re: Yamaha rx775
Post by: Kentakung1 on January 12, 2020, 04:22:27 pm

I. Measure. At. R1225.

140v

Why. Voltage. High. ??

Help me. Please

Title: Re: Yamaha rx775
Post by: pbarton on January 13, 2020, 09:29:02 am

One possibility is that the large capacitor C1085 has gone short circuit.
The bridge rectifier would then deliver it’s full output of 140V, across the other large capacitor, C1084 and R1225.
Unfortunately these large capacitors are only rated at 71V, and consequently you should assume that C1084 has been damaged by the applied 140V.
If correct, then both capacitors would need to be replaced as a matched pair.
Disconnect the capacitors and measure them with whatever test equipment you have available.

Another possibility is that there is a short between the -61V power rail and ground.
Possibly in a different amplifier component, or even within the PCB.
You should be able to confirm this with a simple resistance check.

Title: Re: Yamaha rx775
Post by: Kentakung1 on January 14, 2020, 11:50:00 am

Now.   I have. New problem

R1214. Have. Burn.

But. Can. Power on.

Volume ++

Have. Protect

I measure.  High. Voltage at.  Q1069. And Q1070 is 56 volt

I check.  Transistor. Ok

Title: Re: Yamaha rx775
Post by: pbarton on January 14, 2020, 04:18:29 pm

You still have the original fault?
Do you have +61V and -61V on the two large capacitors C1084 and C1085?
First you have to fix the original fault, before proceeding.

You should have 3.3V at the base of Q1069 and the base of Q1070.
But what do you measure?