Two big problems with my Yamaha CR-2040

Lelle

Active Member
For a couple weeks ago, I bought a preowned Yamaha Natural Stereo Receiver CR-2040. The problem with it from the beginning was a RFI noise, regardless of input and volume it was still there. And wasn't affected by the volume, it was even heard from the pre-out. I have totally recapped the power supply, the pre-amp, pre-drives and the power-amps. And partially recapped the tuner, but the noise was still there. And the tuner dial was often pointing at around 100+. And when I turn up the volume a bit, the right vu-meter points at max in a very short while. I even replaced the little 100uF cap between the huge filter caps. I have totally resoldered everything in the receiver. So that wasn't the problem.

And now to the sad part, while I was measuring the -60 volts on the left amp, I accidentally shorted that pin with the "0" pin right beside on the left main board. (power amp) I powered off the receiver immediately. I know that both left and right amps is sharing the same voltages.

I found out that these transistors where shorted: TR902, TR903 and a small transistor that was placed on a little circuitboard beside the two huge caps. I replaced these three transistors with ones of the same kind. But the protection relay won't click. I can see that the "0" pins on both channels are connected to the relay. I also replaced the TR904 and TR905 without any luck. The fuses are ok, so are all the resistors, diodes and the rest of the transistors aswell. I don't have any oscilloscope, only a DMM. I'm experienced in electronics, and I'm good at soldering.

petehall347 gave me the idea to post this in the Yamaha section instead of the "Vintage Solid State" section. To hopefully get more help and answers to my problem with my Yamaha receiver.

But now i'm out of ideas. And need some advice of what I can do next. I have done anything I could think of.
I have the schematics. (PDF) the parts list is missing.
This receiver is beautiful, and it is worth fixing.

The RFI noise before the accident https://www.youtube.com/watch?v=kNRD...k&feature=plcp

I've measured the voltages on TR902 to TR907, and I got the following numbers:

TR902
Emitter: 87,3
Collector: 7,7 (15 volts when turning of the receiver, before it drops to zero)
Base: 87,2

TR903
Emitter: -82,4
Collector: -83,0
Base: -83,4

TR904
Emitter: -6,0
Base: 7,3
Collector: 87,6

TR905
Emitter: -82,8
Collector: -83,6
Base: -82,8

TR906
Emitter: -9,8
Collector: 8,1
Base: 0,3

TR907
Emitter: -6,0
Collector: -71,0
Base: -6,1


Many of these voltages seems to be incorrect according to the schematic.
 
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I have measured the diodes, and they're seem to be ok.
64.6 ac at the f901 fuse, as I mentioned in my other thread, before I started this thread here in the Yamaha section.
 
I'm not the type of person to give up so easily, but it seems hopeless to fix the receiver. If only I haven't shorted it. :/
If I don't find out the problem, I have to sell it an repair object. And that would be a sad thing to do, as I've always wanted a Yamaha CR-2040. But I have no use for if it isn't working.
 
Starting from scratch...Need to verify some voltages.
1. +20vdc at the emitter of TR915
2. + & - 56vdc measured at the two largest filter caps (+ )terminal and (-) terminal
3. +60 vdc at the emitter of TR904
4. -60 vdc at the emitter of TR905

If you haven't already got them.Get some mini-grabbers for your multimeter.Don't need any more "oops" moments.:thmbsp:
 
Thank u, I will check on that. Sorry if I wasn't logged in for a while, as I took a long break. I will get some mini-grabbers, everyone makes mistakes. It will be a shame to throw it away, or sell it as an repair-objective.
 
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I'll hope someone still reads this thread.
Sorry for not being logged for a long long time.
I had problems with my relationship, my dad got fired from work, bicycle accident. But I am alright now.
So, I took a long break from this receiver.

Now, I measured the voltages:

1. +20vdc at the emitter of TR915 was: (0 vdc)
2. + & - 56vdc measured at the two largest filter caps (+ )terminal and (-) terminal was: +66vdc and -66vdc
3. +60 vdc at the emitter of TR904 was: (8 vdc)
4. -60 vdc at the emitter of TR905 was: (-0.3 vdc)
 
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I'll hope someone still reads this thread.
Sorry for not being logged for a long long time.
I had problems with my relationship, my dad got fired from work, bicycle accident. But I am alright now.
So, I took a long break from this receiver.

Now, I measured the voltages:

1. +20vdc at the emitter of TR915 was: (0 vdc)
2. + & - 56vdc measured at the two largest filter caps (+ )terminal and (-) terminal was: +66vdc and -66vdc
3. +60 vdc at the emitter of TR904 was: (8 vdc)
4. -60 vdc at the emitter of TR905 was: (-0.3 vdc)

Pull fuses F901 and 902 and check them with your ohm meter. If either fuse is bad-replace it.
 
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Power up with a DBT and measure TR904 and 905 collectors.
TR904 collector----- +80vdc
TR905 collector----- - 80vdc
 
TR904 and 905 collectors.
TR904 collector----- +80vdc was: +88vdc
TR905 collector----- - 80vdc was: - 88vdc

The fuses seems to be ok, measuring 1.3 ohms on both fuses.
 
found out that these transistors where shorted: TR902, TR903 and a small transistor that was placed on a little circuitboard beside the two huge caps. I replaced these three transistors with ones of the same kind. But the protection relay won't click. I can see that the "0" pins on both channels are connected to the relay. I also replaced the TR904 and TR905 without any luck. The fuses are ok, so are all the resistors, diodes and the rest of the transistors aswell. I don't have any oscilloscope, only a DMM. I'm experienced in electronics, and I'm good at soldering.

TR902,3,4 & 5

Did you use new transistors or old pulls.
 
TR 903 and 905 sure look suspect. Check your solder connections and correct pin orientation. Look your board over for solder bridges. Check all the ground points in the +/- 60 volt regulator circuit .They should all show continuity to the blue secondary wire off of the power transformer.
 
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I used old pulls, maybe I should replace them with new/better ones.

I will check the board for solder connections bridges and I will double check tr903 and 905, I suspect there something wrong some of these transistors. I'm not giving up.
 
I've checked for solder bridges, and I found a solder bridge on the TR902 transistors collector, fixed it. Replaced it with one of the same kind.
Except for that, I couldn't find something wrong. No poor soldering either.
Maybe I should replace TR 903 and 905 with new ones of the same kind, and maybe TR915 too.
 
Tr903 2sc2240---ksc1845fta
tr905 2sb649----mje350
tr915 2sc1986--tip41c
 
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