ROTEL RA-820BX3 not working

sangeet2 · 04:40 PM

I got a broken ROTEL RA-820BX3 pretty cheap.
When I started to measure voltages I discovered that they are about 4 volts lower then they should be, according to the service manual.

I measured now the voltages at the rectifier and found out that instead of 41 volt they have 37 volt. I assume that the power supply does not work properly now, or?

sangeet2 · 10th February 2012, 04:28 PM

In the service manual is a voltage selector. But it is not on my amp...
Do I have the right service manual?

tvrgeek · 10th February 2012, 04:38 PM

Very old. You may have high leakage of the main supply caps loading it down.
Your measurement is in idle. Correct? No input.
Low rails should not make much difference in it working as an amp, so I think you are not looking att eh correct problem first. What is the bias set at?

GoranB · 10th February 2012, 04:41 PM

Those 4V cant make a big difference. Whats the problem with your amp? Maybe you should be more precise.

sangeet2 · 10th February 2012, 04:43 PM

Quote:

Originally Posted by tvrgeek

Very old. You may have high leakage of the main supply caps loading it down.
Your measurement is in idle. Correct? No input.
Low rails should not make much difference in it working as an amp, so I think you are not looking att eh correct problem first. What is the bias set at?

Yes I measure without input.
Then I took out the fuses which appear after the Transformer. Then I measure an AC of around 25 Volts. So I guess no problem with the caps...
Bias I have not measured yet...

sangeet2 · 10th February 2012, 04:45 PM

Quote:

Originally Posted by GoranB

Those 4V cant make a big difference. Whats the problem with your amp? Maybe you should be more precise.

So far I only put a sine tone on the input and I don't get any signal from speakers output. Only on the record output.
Nothing seems to be obviously damaged, no smoky resistors or similar...

GoranB · 10th February 2012, 04:58 PM

Check F601/602

sangeet2 · 10th February 2012, 05:10 PM

They are working

jaycee · 10th February 2012, 05:19 PM

Check RY601 is switching. If it doesn't engage, the power amps will be muted. If in doubt you may remove it and connect jumpers in its place.

GoranB · 10th February 2012, 05:24 PM

Looking at the schematic i cant see a circuit for the speaker protection, but if the service manual is not the right one, maybe you have those circuit in your amp. If that is a case check if there is a DC voltage on the output, measure at the meeting point of 0.22 ohms ressistors.

9th February 2012, 12:37 PM	#1
sangeet2 diyAudio Member Join Date: May 2009 Location: Berlin	ROTEL RA-820BX3 not working I got a broken ROTEL RA-820BX3 pretty cheap. When I started to measure voltages I discovered that they are about 4 volts lower then they should be, according to the service manual. I measured now the voltages at the rectifier and found out that instead of 41 volt they have 37 volt. I assume that the power supply does not work properly now, or? Last edited by sangeet2; 9th February 2012 at 04:40 PM.

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10th February 2012, 04:28 PM	#2
sangeet2 diyAudio Member Join Date: May 2009 Location: Berlin	In the service manual is a voltage selector. But it is not on my amp... Do I have the right service manual?

10th February 2012, 04:38 PM	#3
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	Very old. You may have high leakage of the main supply caps loading it down. Your measurement is in idle. Correct? No input. Low rails should not make much difference in it working as an amp, so I think you are not looking att eh correct problem first. What is the bias set at?

10th February 2012, 04:41 PM	#4
GoranB diyAudio Member Join Date: Mar 2010 Location: Poland	Those 4V cant make a big difference. Whats the problem with your amp? Maybe you should be more precise.

10th February 2012, 04:58 PM	#7
GoranB diyAudio Member Join Date: Mar 2010 Location: Poland	Check F601/602

10th February 2012, 05:10 PM	#8
sangeet2 diyAudio Member Join Date: May 2009 Location: Berlin	They are working

10th February 2012, 05:19 PM	#9
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Check RY601 is switching. If it doesn't engage, the power amps will be muted. If in doubt you may remove it and connect jumpers in its place.

10th February 2012, 05:24 PM	#10
GoranB diyAudio Member Join Date: Mar 2010 Location: Poland	Looking at the schematic i cant see a circuit for the speaker protection, but if the service manual is not the right one, maybe you have those circuit in your amp. If that is a case check if there is a DC voltage on the output, measure at the meeting point of 0.22 ohms ressistors.

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