Yamaha CR-640 blowing fuse 803

Zach S.

Member
I searched earlier posts and found someone with a similar problem but our issues appear to be different. First ill say i have very limited electronic repair or testing ability. That being said I have a mechanical back ground so if you have patience with me I think I can be guided...lol.

I got this receiver from my uncle. He wanted me to clean it up for him and give it a once over. He bought it at an auction. It was in a room inside a barn. Needless to say it was filthy and exposed to the humidity of New York state. When I brought it home and plugged it in I was surprised to find that it worked. Although all the contacts and pots needed to be cleaned. I began do disassemble the unit and clean it. First i used deoxit cleaner then used the gold deoxit. I let it try for a few hours and then gave it a go. Wow i was impressed. Very good tuner and clean sound. Everything but the meters on the front worked. I figured i would let it warm up a bit and then give it some more power. After 15 minutes at 1/3 I figured the test speakers I was using weren't drawing hard enough cause it was barely warming up. I was on the way to get a bigger set of speakers to hook up when I heard a thud. Blown fuse. I replaced it and tried again. It growled a bit and blew another fuse. I seen in the other post I referred to that the diodes 801 and 802 could be causing the problem. I tested them and they both tested weird so for the $1.19 cost I went ahead and replaced them. I made sure the new replacements (radio shack #IN4003) were installed correctly. I replaced the fuse and tried again. This time it didn't growl but still blew the fuse. I tested the ac output of the orange wire leading to that fuse and it tested 41v. Seemed to be normal? At this point I have no idea what to test. Any help would be greatly appreciated. Thank You!!!
 
Hmmm.:scratch2: My first suspect would be One of the driver chips has shit the bed(shorted out). IC701 or 702 ( IG02950)
 
Im not seeing that on the schematic? I see vr701 and 702 and ic 703 and 704. Which would be the pre driver and power amp respectfully. Am I missing something? I am no expert so I assume I am missing something.

Is there any way I can test that without power? The fuse doesnt last long enough to get a reading...
 
I see it now... Is there a way to test the pre driver without power? If so can you explain how? lol.

I think I read somewhere on another post that if this is the cause then there is no fix because that chip can not be purchased? That sucks if so.
 
With the unit unplugged. Measure the resistance between pin 6 and pin 9,and pin 15 and pin 9 on both chips.Just checking for a dead short between the two rails and ground.
 
looks like a possible problem in the power supply . cap going short or tr803 .tr801

I wanted to eliminate the IG's first.No since troubleshooting any further if one of those are bad.Only place to find a replacement will most likely have a reciever attached to it.
 
The resistance between pins 6 and 9 is .111 and 15 and 9 is .543, both drivers are the same.

Are you using the diode test function? Those look like voltage readings.Use the ohms function not diode function..:thmbsp:
 
Okay. Like i said I am not very skilled at this but have mechanical background... :)


263 for 6 and 9 13.15 for 15 and 9 and thats the same for both drivers.
 
I dont know if this makes a bit of difference or if this would even be a proper way to test something but I was trying to trouble shoot this with my brother inlaw the other day. He is an avionics electronics tech in the navy. He had me check the 2 capacitors below the diodes i replaced which would be b803 and c804. Now when i check those with the ohms function c804 reads 190 and c803 reads .OL as i said i dont know if that means anything or if its even the proper way to test it...
 
Can you post a photo of the power supply section.In the area including C811 & C803 and also C737.
 
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Photo is great.Can you identify C803,811 and 737 in the photo.A few of those caps look like heat has got the best of them. ie shrunken plastic sleeves.
 
Yes i can identify them according to the schematic. I don't know well enough what they should look like I guess. I was thinking that there wasn't anything that looked to bad. Again, I am limited in my ability...lol. So I am guessing the readings on the pre drivers seemed to be ok? This is a capacitor issue then? What would be my next step? Recap? My uncle has just finished up an addition on his house where he is planning on setting up his old TT and put together a record case/display to enjoy his music again. He was hoping this receiver would be the center of it all so it will be under some consistent use if I can bring it back to life.
 
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