Yamaha CR-400 Receiver Needs Repair

[akpasta]

Hello,

I have an old Yamaha CR-400 receiver. Yesterday I was playing it really loud for a while and goofing around with a friend, talking about proper equalization, volume, etc. and I guess we must have been pushing it a little hard because it started emitting a funny smell, then the sound cut out, and it was slightly smoking. Opps.

I pulled the unit apart and found one of the three 250v/2a fuses blown. I replaced the fuse, turned the unit on, and the fuse blew again immediately. It would seem there is a short somewhere, and too much electricity is going to that fuse, and it is doing its job, hopefully preventing damage to my unit.

I am very inexperienced at diagnosing electronic problems. A friend told me to look for "burned or sooty" areas on the board, in an attempt to find a shorted/damaged electrical component and another friend recommended I find a schematic.

If you look to the bottom right of the third fuse, between it and one of the main Caps, the resistor below the smaller capacitors appears burned/sooty, but I cannot read what strength the resistor is, so I don't know how to properly test it. I tried to look it up on the schematic, but I can't read schematics well enough to do so :-(

This receiver functioned GREAT before this happened and was well taken care of. My father was the original owner, and it was passed on to me, so it hasn't changed hands, sat in thrift stores and been caked in dust, etc.

Here are two pictures of the general area, the fuse that keeps blowing has been removed, it is between the two that are pictured. In the second image you can see the resistor in question appears damaged. I located a schematic online (registration required) or I can send it to you in pdf format if you'd like to help me locate what this part may be called and it's resistor labeling so I can test it.

Thank you! Although I sorta know how to use the basic functions of a multimeter and can solder, I am really new at the theory and practice of electronics.

Cr400image

• akpasta
• Nov 23, 2015

Cr400image2

• akpasta
• Nov 23, 2015

 

[akpasta]

Hello!

I read the schematic and I believe I have located the broken resistor. I cannot read the resistor itself, it is too broken, but on the schematic it is labeled as "R701 2P 10," which has no meaning to me. I have also located what may be the fuse that keeps breaking. This doesn't really help me understand why this particular fuse is broken. The resistor that looks burned leads directly to a different fuse that is fine. I am having trouble understanding what is on either side of the fuse that keeps blowing, because I don't understand how to read schematics. The fuse and resistor are both highlighted here.

 

[ConradH]

Looking at the schematic you've almost certainly had a power amp failure. The good news is this unit is all discrete transistors, rather than some impossible to find chip. The bad news is you've got quite a learning curve if you want to fix this yourself, but we may be able to lead you through it. It would probably be better to have someone fix it.

 

[akpasta]

Looking at the schematic you've almost certainly had a power amp failure. The good news is this unit is all discrete transistors, rather than some impossible to find chip. The bad news is you've got quite a learning curve if you want to fix this yourself, but we may be able to lead you through it. It would probably be better to have someone fix it.

Thank you for responding. I have a multimeter and a soldering iron. If I can get to the components and identify their specs for testing/replacement, I can potentially fix anything.

 

[ConradH]

OK, start in the DIY forum and read the sticky on testing transistors. I'd start by checking each output transistor, then work my way back through the various other transistors and diodes in the power amp. Remember that no resistor or fuse fails on its own, but because too much current flowed through it. Thus, replacing those without finding the real failure will just result in more burned resistors and open fuses! I'm also sending you a PM.

 

[akpasta]

OK, start in the DIY forum and read the sticky on testing transistors. I'd start by checking each output transistor, then work my way back through the various other transistors and diodes in the power amp. Remember that no resistor or fuse fails on its own, but because too much current flowed through it. Thus, replacing those without finding the real failure will just result in more burned resistors and open fuses! I'm also sending you a PM.

Thank you! I'll dig in!

 

[avionic]

Any luck so far ?

 

[Jpete9]

I cant help, but i can offer encouragement. While not everyone posts in these threads, plenty of read and follow them - keep coming back with your learnings. Its interesting and it may well help some one else in the future.

GOOD LUCK!

 

[akpasta]

Thanks for the encouragement. Unfortunately getting to the components I need to remove to test is going to be all of the battle. I might have to de-solder tens of wires and take the entire unit completely apart to get to the two diodes and the one transistor I need to test. This is rather discouraging, and making me consider taking it somewhere for repair, rather than spending hours taking everything apart and putting it back together.

What I could use, is some advice of the fastest way to get to D701, D702 and TR618. Either the two former parts, which make up the rectifier are friend, or the transistor is fried. I can't test either of them without removing them but I can't remove them without--as far as I can tell-- desoldering and removing a bunch of other wires and taking the entire main power board out of the unit.

 

[ConradH]

Can you get at them to probe in-circuit? If so, what sort of readings do you get?

 

[39cross]

"R701 2P 10

this is translated into 2 watt, 10 ohm resistor

 

[Half Life]

The R701 2P 10 is a metal oxide type, 10 ohm, 2W resistor. The parts list denotes it as HL42410.

If you can't get to the individual parts to test them, you are going to have to remove some wires to give yourself room as you already know. When you locate the bad parts, you'll need to removes wires anyway for the repairs. Take your time and document where every wire goes. When doing these types of repairs I take lots of pictures and use Brady labels to identify wire locations. Good luck!