Yamaha CR-640

The Rebel

Active Member
Howdy. I have a nice looking CR-640 that I've just had the chance to open up after a period of it sitting on my stash table. Popped the lid, and cleaned it up a bit, it wasn't bad at all. Plugged it in and hit the power button. It "lights up", but that's it. No relay click. I have read a few posts on these receivers and have seen a couple of videos on you tube. One guy says his receiver did not click in until he "adjusted two pots" on the main board, and replaced one diode. He never got into that procedure in his video to let the cat out of the bag as to what he actually did to it to get it going again.
So I got the manual out and proceeded to check DC offset on TL, and TR on the main board. I got a reading of -143.7mv on the left(TL), and a reading of 31.8v on TR. I was able to adjust TL to 0v, not so lucky with TR, as there is no change when I turn the pot for DC-R.
At this point, I'm in need of direction on what to look at next. Any help from the Yamagods will be greatly appreciated. Thanks.
 
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Check your meter setting as 143V is higher than would show up in that unit. Maybe mV? Avionic will be by shortly to guide you. Hopefully your NLA, no replacements available, driver IC is not toast.
 
. I got a reading of -143.7v on the left(TL), and a reading of 31.8v on TR. I was able to adjust TL to 0v, not so lucky with TR

Very good possibility that one of these has expired.
IC704--- IG2980 final or IC702--- IG2950 driver power packs- possibly bad in the Right channel.
 
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Ooops.... you are correct sir. -143.7mV . I thought I scanned that post for errors before I posted. :( :crazy:
Check your meter setting as 143V is higher than would show up in that unit. Maybe mV? Avionic will be by shortly to guide you. Hopefully your NLA, no replacements available, driver IC is not toast.
 
Compare the voltages between IC 703 and IC 704 pin for pin. As well as IC701 and IC702. They should be pretty close to identicle.
 
Be very very careful not to short out adjacent pins. One slip and if it wasn't bad it will be bad in a nanosecond.
 
Here are the readings on both L/R driver, and L/R output chips.
IC-701(L driver) IC-702 (R driver)
1. 27v 27v
2. 2.95v 27v
3. -3.04v 3.4v
4. -2.7v -36.2v
5.-31.5v -38.9v
6. -13mV 32.1v
7. -.5mV -.5mV
8. 19.5mV 33.1v
9. 2.6v 32.47v
10. -40.3v -40.3v
11.-41.3v -41.3v
12. -39.8v -38.5v
13. 78.7mV .47mV
14. 3.3mV 3.2mV
15. 78mV 180mV

IC-703(L output) IC-704(R output)
1.-2.96v 2.62v
2. -40.2v -40.6v
3. -2.9mV -40.2v
4. -1.7v 8.03v
5. -.55v 8.9v
6. .59v 28.11v
7. 1.77v 11.45v
8. 27.5mV 39.2v
9. 40v 40v
10. 2.94v 35.37v
This was the first time I had it on this long to check all these and the right output got warm to the touch, while the left was still cool.
 
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Don't know what next. But this didn't look real good. That light tan sucker looks a little crispy on the bottom. The two caps may have leaked, dunno.
 

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Right output doesn't look very healthy. Right driver voltages may be skewed by the output voltages. I'd say your IG is trashed ( IC704). Possibly the driver as well.
 
Ok. If I remove IC704, would that possibly get the protection relay to close, and have the left channel operating? I'm not finding how to test IC-702 to determine which is the culprit. I've gotten two receivers(780s) going this week so far, having FM tuner issues with one of them. I really want this one back up and running, seems like a good one. Thanks for the help with this, avionic.
 
If I remove IC704,
Should be able to remove the 704 and make sure the solder pads are clean with no solder bridges. Then remeasure voltages on IC702.Hopefully there a might bit closer to the 701's pin out voltages.
 
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Just checking back in with an update, didn't want to leave this open ended. I am in the process of pulling the right channel output off of the pcb to further test the driver and the output chip. I've gotten most of the solder out of the pins and holes, but I am not liking the results. I ordered a desoldering gun to finish the work on this one. Will let you know how it turns out once the new toy comes in. Thanks for all the replies.
 
Alright! Finally getting back to this project, sorry I took so long, but life happens to the best of us. Bringing this back up, the protection relay would not click in on this receiver. I checked DC offset at the speaker terminals and it was deemed that the right channel was dead. So after checking voltages at the pre drivers and amp outputs I was instructed to remove the right channel output chip to see if the protection circuit would click in. That's when I hit a snag desoldering with a solder sucker, that just wasn't giving me any love, so I ordered a desoldering gun to further this addictive hobby. I like my new toy, it makes PCB work a breeze. I removed the right channel output chip from the board and got the relay to click in when I powered it up. Yay! Hooked up a speaker to left channel, and it sounds strong. That's where I am at the moment. I am thinking of pulling the left channel output chip and soldering the right channel output in it's place to check for output. Is this a safe thing to do, or am I risking popping an output doing this? Pull the drivers?

I can give voltage readings at both pre drivers after the right channel output was removed, as they are different now, if this will help with the diagnosis. I'll post it as before and after.

Here are the readings on both L/R driver, and L/R output chips.
IC-701(L driver) IC-702 (R driver)
1. 27v 27v After 39.4v 39.4v
2. 2.95v 27v After 2.95v 39.1v
3. -3.04v 3.4v After -3.04v -40.6v
4. -2.7v -36.2v After -2.68v -40.2v
5.-31.5v -38.9v After -18.5v -390.1mV
6. -13mV 32.1v After -1.1mV 27.1mV
7. -.5mV -.5mV After -.1mV .1mV
8. 19.5mV 33.1v After 21mV 372mV
9. 2.6v 32.47v After 2.6v 38.8v
10. -40.3v -40.3v After -41.3v -41.3v
11.-41.3v -41.3v After -40v -40v
12. -39.8v -38.5v After -39.9v -40.1v
13. 78.7mV .47mV After 89mV 175.8mV
14. 3.3mV 3.2mV After 12.8mV 12.9mV
15. 78mV 180mV After 88mV 172.7mV
 
Bringing this back up, the protection relay would not click in on this receiver. I checked DC offset at the speaker terminals and it was deemed that the right channel was dead.
With the protect relay not "setting" you can't measure the DC offset at the speakers.
 
With the protect relay not "setting" you can't measure the DC offset at the speakers.
You are correct, I wrote that wrong, I checked those at the amp board when I did that. Left channel was good, right was dead.

Kinda looks like it to me.

Would you risk swapping the output chip from the right (dead)channel into the left channel to see if it is good? Or just try to find a replacement output chip? Thanks for all the help.
 
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