Help Required for Rotel RX-975 Receiver Repair - diyAudio
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Old 15th January 2013, 04:38 AM   #1
dtm1962 is offline dtm1962  Canada
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Default Help Required for Rotel RX-975 Receiver Repair

I am currently fixing my buddy's receiver.

It was totally dead with absolutely no functionality. The fuses were all good on the main primaries, standby secondary & the main PCB board fuses on the power supply rails for the power amp section.

So I troubleshot and have fixed the standby transformer which pins were separated from the PCB solder terminals.

So now I got the following limited functionality:

1) Relay on Standby board functions correctly
2) Correct voltages as required (+5V; -30V etc.) to front control board
3) Remote control will initate Standby as well as getting out of Standby
4) On-board standby pushbutton will function as normal
5) Remote control will initiate Speaker A & B or off as initiated
6) On-board pushbutton speaker select will function as normal
7) LED indicators for Speakers & Standby function correctly
8) Background LED Control display shows very faint "orange background only"

So what doesn't work:

1) Nothing else functions as per on-board pushbuttons/controls or by remote
2) No actual displayed alpha numerical characters

So any help would be appreciated.

Thanks,
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Last edited by dtm1962; 15th January 2013 at 04:41 AM.
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Old 15th January 2013, 05:47 AM   #2
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Hi,
You do not mentioned that you check the +/- 15 volts? Did you check the +15/-15 volts?
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Old 15th January 2013, 01:30 PM   #3
dtm1962 is offline dtm1962  Canada
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Default More Measurements Performed

Quote:
Originally Posted by tauro0221 View Post
Hi,
You do not mentioned that you check the +/- 15 volts? Did you check the +15/-15 volts?
Yes I just double-checked the +/-15VDC and while I was at it I confirmed the +/-55V to the Power Amp Board as well.

I am thinking maybe the Main Controller Chip on the front Board which controls the LED Display as well as the controls everythingh else is at fault?

Let me know what you think?
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Old 15th January 2013, 01:43 PM   #4
jaycee is offline jaycee  United Kingdom
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sounds like the microcontroller isnt running. Check nearby for an xtal or resonator, make sure it's producing a clock.
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Old 15th January 2013, 02:36 PM   #5
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Also check the Vdd voltage at the front panel micro. I think you can check it easily at the diode D619.Should be 5 volts
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Old 15th January 2013, 03:22 PM   #6
dtm1962 is offline dtm1962  Canada
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Quote:
Originally Posted by tauro0221 View Post
Also check the Vdd voltage at the front panel micro. I think you can check it easily at the diode D619.Should be 5 volts
I checked the Vd at the Microprocessor Chip and I get 5VDC

I also checked the Xtal and I get 5VDC on 1 pin & 0V on the other & 0V on the GND pin.

Also I measure 5VDC on the RST pin as well.

The FL1 & FL2 (Display power) I measure -19VDC as well at the display.

Any ideas?

Thanks in advance.
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Old 15th January 2013, 04:26 PM   #7
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Hi,
Let try to force a reset in the micro. Be careful jump pin 37 and 38 to the micro this will ground the reset and the micro should initialize if it working. Also do you have a scope? By checking pin 10 and 11 with the scope we will know if the micro it is running. You should see clocks coming out at those pins.
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Old 15th January 2013, 04:41 PM   #8
dtm1962 is offline dtm1962  Canada
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Quote:
Originally Posted by tauro0221 View Post
Hi,
Let try to force a reset in the micro. Be careful jump pin 37 and 38 to the micro this will ground the reset and the micro should initialize if it working. Also do you have a scope? By checking pin 10 and 11 with the scope we will know if the micro it is running. You should see clocks coming out at those pins.
Hi:

Thanks for the input.

I will force a reset & I do have a scope to check out the Xtal waveform etc.

I am on my way to work now but I will give it a try as per your instructions tonight.

Thanks for your help.

Stay tuned!
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Old 16th January 2013, 01:05 AM   #9
dtm1962 is offline dtm1962  Canada
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Default SUCCESS!

Quote:
Originally Posted by tauro0221 View Post
Hi,
Let try to force a reset in the micro. Be careful jump pin 37 and 38 to the micro this will ground the reset and the micro should initialize if it working. Also do you have a scope? By checking pin 10 and 11 with the scope we will know if the micro it is running. You should see clocks coming out at those pins.
I hooked up the scope to the Xtal and thwn suddenly I hear the Standby Relay click off. So I turned off the power and turn back on then the Blue LED Display came back to LIFE and I have full functionality!

Thanks Guys! (especially tauro0221)
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Old 16th January 2013, 01:11 AM   #10
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Hi,
Congratulations??? good job. Check the crystal for a bad solder joint or replace it if it failed again.
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