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CR640 help please
- Thread starter Magn
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The protection circuit in a CR-640 only senses DC voltage at the power amplifier outputs. Does it still sound good when turned up to just below the threshold where it cuts out? If so, I can only think that capacitor C901 in the protection circuit has failed. (I think it should be replaced with a bi-polar part, by the way, even though apparently a polar part was used originally.)
If the receiver starts to sound like hell before it cuts out, you might have a power amp problem. You didn't mention anything like that, so my assumption would be that the power amps are OK.
Power amp adjustments in a CR-640 are only for DC offset. (There is no adjustment for bias.) My assumption is that this is not the cause of the problem, since the problem only occurs at high-ish volume.
Could be a dirty Volume control. Or any of the switches that the signal goes through.
I would clean them all before touching any caps or stuff.
Like the speaker selector switch, Mono stereo switch, Balance control, Volume , etc.
Also try tapping on the speaker relay while its playing with a non metallic instrument to see if it might be the relay.
Athanasios
I would clean them all before touching any caps or stuff.
Like the speaker selector switch, Mono stereo switch, Balance control, Volume , etc.
Also try tapping on the speaker relay while its playing with a non metallic instrument to see if it might be the relay.
Athanasios
Please bear with me as I have no experience with this stuff. Just a farm boy that’s been around a lot of stuff and wants to eliminate the obvious before seeking technical help. I would think if one channel works well that would eliminate common controls such as volume but I probably don’t understand how it works. I tried changing the speakers from a to b and the problem stays the same. Likewise I switched speakers from L to R and got the same result on the other speaker. One other thing I noticed was the bulbs over the tuner dial were not working but the bulb for the dial indicator was working. Thanks for your help.
I love Athanasios' optimism, but I don't think this particular cutting-out symptom can be caused by control hygiene problems. I think the protection circuit is operating, and I think that is because there is a power amp problem in the channel that is distorting, most likely a open device in the "power pack" (Yamaha part IG02980, generic part STK0050II).
Yabut, these days you can get viable replacements for at least the STK power packs. I have in mind the discrete-component modules offered by AKer rcs16 or Pyramid Audio, not the dubious parts available from the Far East. I like the rcs16 electronic design better, but I don't think it will physically fit in a CR-640, so the Pyramid "STK0050+" is probably the way to go.
Cost will likely be an issue, in any case. I think it could only be sentimental value that could justify the expense of something like the above for a CR-640.
Cost will likely be an issue, in any case. I think it could only be sentimental value that could justify the expense of something like the above for a CR-640.
Sparkplug
Super Member
Looks like they are different power STK modules. If so, can’t run the amp with different power level in each channel. Well you could, but it’d be bizarre. I have not read the thread btw and am only commenting on the different STK usage.
Could be.
How the heck did somebody shoe-horn an "80"-sized pack into a CR-640? (Never mind why?)
It looks like the "80" pack might not be sitting flat on the heat sink. If that is so, it's a problem for that channel, whether that pack is currently functional or not.
The "40" is not a correct part, either. It should be an STK-0050II.
All properly-made STK00x0II packs are electrically very similar for low output levels, and will more or less work at such levels. The main difference is their ability to handle higher power levels, and their package size.
I continue to think that replacing the pack in the distorting channel with a 50-watt Pyramid module is a sensible thing to do, at least from a functional point of view. Whether it makes sense economically is another question.
(If the other pack is indeed ill-fitting mechanically, then it should also be replaced.)
It looks like the "80" pack might not be sitting flat on the heat sink. If that is so, it's a problem for that channel, whether that pack is currently functional or not.
The "40" is not a correct part, either. It should be an STK-0050II.
All properly-made STK00x0II packs are electrically very similar for low output levels, and will more or less work at such levels. The main difference is their ability to handle higher power levels, and their package size.
I continue to think that replacing the pack in the distorting channel with a 50-watt Pyramid module is a sensible thing to do, at least from a functional point of view. Whether it makes sense economically is another question.
(If the other pack is indeed ill-fitting mechanically, then it should also be replaced.)
@Magn Ali Express has clone STK-0050 II for $5.81. They may not be NOS, but it's hard to see how much worse they could be than the hodgepodge you have on your hands now.
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