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CR-220 Burnt Resistor

HotRodStereo

HotRodStereo

New Member
Hi All,

I opened up this Yamaha last night that I purchased broken, it has what sound like a 60Hz hum and It looks like the culprit is this burnt section here, the only trouble is that the resistor thats burned out in my photo doesn't seem to exist on this diagram, its simply marked with an "r" on the pcb. Beneath the resistor in the photo. Anybody have any ideas? repair.jpghttps://www.hifiengine.com/manual_library/yamaha/cr-220.shtml
 
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The big problem you run into is revisions of the circuit during production. So my advice is to start looking around for a schematic that matches this unit. It is a real PIA. I was looking at what is available for your CR-220 and there are a lot of choices. The CR-220 was made form 1977 to 1980.
 
It looks like the corresponding resistor on the other channel would be right above TR703, which obviously is a different resistor. I noticed some scorching on the capacitors adjacent to the toasted resistor, I think my next course of action is to pull out any suspicious componenets on that channel and check them?

As far as the service manual versions go, the only ones that I can find scanned in so far are circa 1977, so early production. I was able to find someone elses post on here that has a photo of the amp section and it shows the resistors installed, with my suspiciously burned spot looking much more like the other channel. - https://audiokarma.org/forums/index.php?attachments/16358134101502979704233305600504-jpg.2383739/
 
I Think you have a modification, or a repair. That is a carbon composition resistor. All of the other resistors are carbon flim resistors.

I found this photo of the CR-220 PSB. The resolution is not too good but you can just see there might be resistor located were your mystery resistor is located

IMG_8254.jpeg

That might just be a solution have someone with a CR-220 take a HiRez photo of this board.
 
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transmaster said:
I Think you have a modification, or a repair. That is a carbon composition resistor. All of the other resistors are carbon flim resistors.

I found this photo of the CR-220 PSB. The resolution is not too good but you can just see there might be resistor located were your mystery resistor is located

View attachment 3001578

That might just be a solution have someone with a CR-220 take a HiRez photo of this board.
Click to expand...
My thoughts exactly. When i first glanced at it I thought it may have been a diode, but obviously there is a carbon film on the other channel. Its hard to even tell what it is with the level of toasted at play here.
 
Just checked there are several CR-220 for sale a eBay going fairly cheap. A board transplant? or just a clean working example to upgrade.
 
HotRodStereo said:
My thoughts exactly. When i first glanced at it I thought it may have been a diode, but obviously there is a carbon film on the other channel. Its hard to even tell what it is with the level of toasted at play here.
Click to expand...
That is a 1/2 watt resistor if something in that circuit fried a 1/2 watt resistor I would be really thinking about what caused it burn up.
 
transmaster said:
That is a 1/2 watt resistor if something in that circuit fried a 1/2 watt resistor I would be really thinking about what caused it burn up.
Click to expand...
I am going to have to trace it back, one of the reasons i was hoping for a diagram was to see what fed it that much sauce.

Iits hard to see in this photo, but the electrolytic right next to it looks burnt on the bottom, and the ceramic is even a bit singed. It seems to me though that the resistor is the most toasty.
transmaster said:
Just checked there are several CR-220 for sale a eBay going fairly cheap. A board transplant? or just a clean working example to upgrade.
Click to expand...
If i was going to keep it I probably would, but I purchased the unit with a few others in need of repairs to learn how to "fix em right" and diagnose effectively. I only have about 15 bucks into this one, so i would prefer to troubleshoot and solve.
 
Just found this tip for scoping out the value of a fried resistor.

  1. Scrape the outer coating.
  2. Clean the burnt section of the resistor.
  3. Measure resistance from one end of the resistor to the damaged section.
  4. Again measure the resistance from the damaged section to the other end of the resistor.
  5. Add these two values of resistances
Talk about a smack your forehead no brainer.
 
petehall347 said:
the manual on hi-fi engine has the board view
Click to expand...
Its hard to see in the manual, but there is a separate schematic on HiFi Engine that shows more clearly, Its tough to tell what resistor that is since they arent marked on the PCB, but i will go through it tonight with the process of elimination and see if i cant find it. Im going to test the other channel's resistor for the value and see if its on the schematic.
 
deleted this reply ..i made a mistake .. anyway the resistor connects to TR708 and looks like 33 ohms Screenshot from 2023-10-04 20-50-34.png
 
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petehall347 said:
deleted this reply ..i made a mistake .. anyway the resistor connects to TR708 and looks like 33 ohms View attachment 3001652
Click to expand...
Haha I was looking for the old one like.. Damn why cant i find it!

I think you are right, its not given a number on the schematic either which would give reason to its absence on the diagram. I will give it a look tonight and check ole TR708 (among others) to see if that caused the issue. C706 and 714 are in the mail for replacement. TR707 has the same 33 ohm resistor.
 
1696454605168.png1696459274454.png

R764 -- 33 Ω 1/4 watt flameproof -- carbon or metal film .. " Macht nichts"
 
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