Yamaha Cr-640 blowing fuse

gp1680

Active Member
Recently acquired a CR-640 that was not working. First test of the receiver had all lights working, but no sound and no activity on the tuner. Took the cover off and found that there are two fuses on the driver board. One 2a and one 1.5a. There was no 1.5a fuse present. I replaced with correct fuse. Immediately upon power up, the fuse blew. Now I know why it was missing. Any suggestions/ideas on where to start? I do not have schematics for it. Thanks!
 
You most likely have a power supply issue. I'm sure the Yammie techs will chime in but I'd be looking at troubleshooting your output transistors and the likes. It's worth fixing, so don't get discouraged. Lots of friendly AKers here willing to lend a hand if you ask politely and have patience. :yes:

I just picked up a beautiful CR-620 for a gift to a relative, but I'm now torn about holding on to it. Yamaha natural sound is addictive. :D
 
Thanks Max. This is my first Yamaha and I'm dying to hear what it sounds like. I know it's worth a shot.

To all the "Yammie" techs -:ntwrthy: PRETTY PLEASE!! :ntwrthy:
 
The 1.5A fuse is for two B voltage supplies (pos and neg) to the pre drivers and power amp modules as well as sections of the tuner board. There are two diodes very near the fuse itself, if either of them is shorted that would also blow the fuse.
 
http://audiokarma.org/forums/showthread.php?t=154865
Follow the instructions for a pdf schematic.
I have not worked on one of these yet.But I glanced over the diagram. Your problem could be a power supply issue or a shorted hybrid chipamp pack. Does the blown fuse have a F number like F01 or F02?

Thanks Avionic! I've got the schematic now. There was no original fuse present when I got the receiver. I replaced the 1.5a with the same. The only designation I could find on the new fuse was "AFE".
 
Rob (Merrylander) has probably serviced a few of these. Look at the schematic power supply section for the fuse designator AFE follow the path to the right of the fuse and locate the diodes Rob is referring to.You may have to lift one lead of each diode to check with a DMM. Looks like diodes are D801 and D802..

AFE isn't a reference designator.Probably a model number. Looks like there is only the two fuses on the board and one is for the lights..process of elimination. The diode D803 is for the lamp circuit as well.If you still have lights working that diodes OK.
 
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UPDATE:

I tested both diodes immediately to the left of the fuse. One of the diodes had zero resistance both ways. I replaced it. Now, the fuse does not blow but I still have zero output and no activity on the tuner meters. I've heard that these units sometimes had bad solder connections. Could this be the problem now? Next step? :scratch2:
 
Well you'll probably have check transistors in the power supply TR801-805. Which diode did you replace? I take it there was no relay " click"..:scratch2:
Theres a bunch of electrolytic caps in that circuit..Do any of them look maybe bulged with the plastic sleeve shrunk down ? Boy a picture here would really be helpful. That schematic on hifiengine sux -- no reference voltages..Other than AC off the transformer.:thumbsdn:
 
Now you get to check the pre-driver ICs. Remove the bottom cover and lay the 640 on its back. The ICs are those flat black rectangular gizmos wit 15 pins, pin 5 is not soldered. Pins 13 and 14 should have very little voltage on them, if they have around 40V DC on them they may well be toast.
 
Well you'll probably have check transistors in the power supply TR801-805. Which diode did you replace? I take it there was no relay " click"..:scratch2:
Theres a bunch of electrolytic caps in that circuit..Do any of them look maybe bulged with the plastic sleeve shrunk down ? Boy a picture here would really be helpful. That schematic on hifiengine sux -- no reference voltages..Other than AC off the transformer.:thumbsdn:

It was either D801 or D802, I could not pinpoint it on the schematics. There is no relay activity either. The electrolytics looked okay, but I'll have to double-check. I'll try to get a pic as soon as I can. There was a family emergency this morning and it now takes utmost precedence. I will update both you and merrylander as soon as I run some more tests, including the IC voltage check. Thanks for the info!
 
The driver IC likes to fail internally, and one or both of the amplifier offset voltages will go to the of the supply voltage rails.

When you replace the driver IC (if it is bad) always look for OLD STOCK.

Fred
 
Okay, the diode that was replaced was D801 directly off of fuse F803. The schematic lists the diode as 1S1886. I replaced it with a 1N4003 1a 200V from Radioshack.

I tested pins 13 and 14 on both IC's and found very little voltage.

I attached pics.

I found something that maybe interesting. I tested the voltage coming off the f803 fuse into the lead of the diode. It is 40V. It's supposed to be 39V according to the schematics. That's okay. However, there is no voltage coming off of the other lead of the diode. Am I missing something? Is that the way it's supposed to be? It don't seem right. I'm also not getting any voltage on C800 and C801. I'm guessing this is the problem. A bad capacitor C800 or C801?
 

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Check C803 and C804 for voltage, it should be positive on the + lead of C803 and ngative on the can of C804. The CR-840 power circuit is identical in this area and its schematic shows + 53.6V or -53.6V. The emitters of TR801 and TR802 should regulate this to approx + or - 41V.
 
The only voltage I'm getting on either one is +124 on the positive lead of C804. There is nothing at all on C803 or neg on C804.
 
Check C803 and C804 for voltage, it should be positive on the + lead of C803 and ngative on the can of C804. The CR-840 power circuit is identical in this area and its schematic shows + 53.6V or -53.6V. The emitters of TR801 and TR802 should regulate this to approx + or - 41V.

Forgive me for my stupidity and lunacy. My mind has been on other things this weekend and only realized now that I did not test the circuit on DC. Ughhh!

Merrylander - I retested the positive lead of C803 and got +57.1V. The negative on C804 was -58.1V.
 
Okay, just tested TR801 and found readings of .03, 56, and .03. That don't seem right. According to your post Merrylander, at least one of the leads should be in the 41V area? Is the TR801 toast?
 
It sounds like it, when I get a chance I'll post all the voltage readings for TR801 and TR802.

OK TR 801 looking at it from the face is E C B, TR802 looking at it from the face is B C E.

TR801 E = 41.2, C = 53.6, B = 41.2

TR802 B = -41.2, C = -53.6, E = -41.0
 
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It sounds like it, when I get a chance I'll post all the voltage readings for TR801 and TR802.

OK TR 801 looking at it from the face is E C B, TR802 looking at it from the face is B C E.

TR801 E = 41.2, C = 53.6, B = 41.2

TR802 B = -41.2, C = -53.6, E = -41.0

Thanks Merrylander!! Sorry it took so long to respond back. I've been kinda' busy.

The emitter and base voltages on my TR 801 are .03. I guess that means it's toast?? Now I just have to find a working replacement. Anyone have a CR-640 they wish to part out???
 
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Take a close look at TR804 in the photo... blammo?

fyi:
TR804 is a 2SA999 Equiv. Subs for it would be :

2SB882 (Sanyo)
2SB1022 (Toshiba)
2SB1113 (Hitachi )
2SB951 (Matsushita )
2SB1344 ( Rohm)
Pretty sure that the problem was resolved 14 years ago..
 
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