Yamaha RX1130 R&L input signals mix in the output section - diyAudio
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Old 14th March 2015, 06:51 PM   #1
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Default Yamaha RX1130 R&L input signals mix in the output section

I have a Yamaha RX1130 that was snagged at the dump about 4 yrs ago. First component that I repaired, way before what I know now but ended up replacing about 7 components, one output device, on the amp board. Did get both channels operating. Listened to it for several months giving it some hot suppers before I finally realized it was in mono? Now remember this was way before any learning that I have done so back then I brought it to a couple shops that wanted nothing to do with it which now I understand. But I could put that back on the bench and see if I can determine what is going on. I purchased the repair manual back then for the shops to use.
What's happening is when the balance knob is turned to 1 channel the volume level decreases a bit on both channels and audio with equal volume level comes out of both channels. Wouldn't that mean somewhere upstream the input signals are mixing?
Let me answer that. I just went downstairs and pulled the jacks between the amp and preamp. Proceeded to hook up a portable CD player putting the signals straight into the amp. both channels operating but when I pull either of the input signals sound still comes from both speakers. in my simple mind that seems to be a positive because it means that the signals are not mixing somewhere upstream from the amplifier section that could be difficult for me. It would seem all I have to do is troubleshoot the power amplifier board.
Attached Files
File Type: pdf amp power board schematic.pdf (259.3 KB, 26 views)
File Type: pdf amp power board schematic1.pdf (312.7 KB, 12 views)
File Type: pdf marked up amp section showing replaced parts_measured values.pdf (438.5 KB, 11 views)
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Old 14th March 2015, 06:54 PM   #2
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Default Yamaha RX1130 R&L input signals mix in the output section

visually R200 on emitter circuit of Q138 looks smoked. Measures open.

checked TP- /TP+ should measure 6-8mV measure 0mV probably no surprise if R200 is open. Is this the bias current? Also measured DC offset right channel 83mV and the left channel measured 90mV. See attached color coded amp schematic. Attempted a measurement of R200 insitu and it appears to be open. Really ticks me off that neither of the attempts to get it looked at was the basic bias and DC offset measurements taken. The measurement at TP- / TP+ right channel might have been a big flag. The place in Cambridge Boston, Audio Lab, is supposed to be a reputable place?
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Old 14th March 2015, 07:24 PM   #3
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I would recommend not messing with the fonts so much. It just so happens that - *gasp* - people may actually want to be able to read what you write without having to crawl into the screen.

Full quote with the offending tags removed:
Quote:
Originally Posted by rfitts46 View Post
I have a Yamaha RX1130 that was snagged at the dump about 4 yrs ago. First component that I repaired, way before what I know now but ended up replacing about 7 components, one output device, on the amp board. Did get both channels operating. Listened to it for several months giving it some hot suppers before I finally realized it was in mono? Now remember this was way before any learning that I have done so back then I brought it to a couple shops that wanted nothing to do with it which now I understand. But I could put that back on the bench and see if I can determine what is going on. I purchased the repair manual back then for the shops to use.
What's happening is when the balance knob is turned to 1 channel the volume level decreases a bit on both channels and audio with equal volume level comes out of both channels. Wouldn't that mean somewhere upstream the input signals are mixing?
Let me answer that. I just went downstairs and pulled the jacks between the amp and preamp. Proceeded to hook up a portable CD player putting the signals straight into the amp. both channels operating but when I pull either of the input signals sound still comes from both speakers. in my simple mind that seems to be a positive because it means that the signals are not mixing somewhere upstream from the amplifier section that could be difficult for me. It would seem all I have to do is troubleshoot the power amplifier board.
Quote:
Originally Posted by rfitts46 View Post
visually R200 on emitter circuit of Q138 looks smoked. Measures open.

checked TP- /TP+ should measure 6-8mV measure 0mV probably no surprise if R200 is open. Is this the bias current? Also measured DC offset right channel 83mV and the left channel measured 90mV. See attached color coded amp schematic. Attempted a measurement of R200 insitu and it appears to be open. Really ticks me off that neither of the attempts to get it looked at was the basic bias and DC offset measurements taken. The measurement at TP- / TP+ right channel might have been a big flag. The place in Cambridge Boston, Audio Lab, is supposed to be a reputable place?
As for your problem, if the two channels mix like that, there are only two things that could be wrong:

1. Signals are shorted together somewhere.
2. There is a bad ground connection somewhere, up to and including the speaker terminals and power supply section. Ribbon cables and such may be worth checking, though with some bad luck it could be a cracked PCB as well. Make sure there is continuity between speaker return and transformer secondary center tap (or between the big filter capacitors). Same goes for the input side.

I'll go have a look at the docs now...

R200 is not essential for the function of the amplifier, but it being smoked indicates that significant current must have flown through the outputs, in line with what you state. Have you found any burnt traces? Is Q140 still alive and kicking (or replaced)?

Last edited by sgrossklass; 14th March 2015 at 07:40 PM.
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Old 14th March 2015, 07:31 PM   #4
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Default Yamaha RX1130 R&L input signals mix in the output section

decided to look at the first two transistors that the signals hit Q105 and Q106 muting function. Is the schematic wrong or is the emitter of Q105 supposed to be connected to the collector of Q106. On the board it appears that their collectors are connected to E.
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File Type: png muting section.png (133.6 KB, 65 views)
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Old 14th March 2015, 07:38 PM   #5
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sgrossklass, sorry was copying and pasting text from elsewhere instead of typing directly into forum. will stay aware of that.
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Old 14th March 2015, 07:42 PM   #6
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Quote:
Originally Posted by rfitts46 View Post
decided to look at the first two transistors that the signals hit Q105 and Q106 muting function. Is the schematic wrong or is the emitter of Q105 supposed to be connected to the collector of Q106. On the board it appears that their collectors are connected to E.
Probably a misprint, though I'd guess with muting transistors it doesn't matter so much anyway (they need to have high reverse beta).

Updated my previous reply.
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Old 14th March 2015, 07:51 PM   #7
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Quote:
R200 is not essential for the function of the amplifier, but it being smoked indicates that significant current must have flown through the outputs, in line with what you state. Have you found any burnt traces?
I have at this point looked the entire board over using magnification. I don't believe there are any burnt traces. What caused the original failure was a liquid short between J213 and J249. The original repair effort was years ago but I do remember that the ribbon cable from the predriver board was removed. I remember trying to get it reconnected, it was not for the light hearted.

Last edited by anatech; 16th March 2015 at 07:23 PM. Reason: Opening quote tag was missing
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Old 14th March 2015, 08:39 PM   #8
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Default Yamaha RX1130 R&L input signals mix in the output section

while I was identifying the jumpers that had shorted decided to check emitter resistor values. Measure .22 ohms across R182, R184, R186. Measured 10ohms across R188 the emitter resistor for Q138?

will manually ring out the ribbon wire cable removed during the predriver board repairs.
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Old 14th March 2015, 11:49 PM   #9
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Sgrossklass, will check out Q140. What is the function of Q140..some type of protect..overcurrent?

Last edited by rfitts46; 14th March 2015 at 11:58 PM.
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Old 15th March 2015, 02:25 PM   #10
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Q140 measures:

65V on collector should be 71V(rail supply)
0V on base should be 0V
250mV on emitter should be 0V

Because Q140 collector should be at 71V went back to PS.
Measured 45.5Vac across transformer secondary instead of 52.3Vac.

Question is can the transformer secondary be good while something downstream is dragging it down?
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