• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Yamaha CR-640: Lights up but no sound.

C

ChuckSunset

New Member
Hi AudioKarma,

I am not a very smart man. I was recently gifted my father's Yamaha CR-640. The unit sounded great, it was just missing some lamps. I got replacement lamps today and replaced all four above the tuner. Now, this is where I made a HUGE mistake... I turned the unit on to make sure the lamps worked and then I tried to tighten one of the lamps with my pliers... :(. Needless to say, there was a spark, and then a loss of light and audio. I inspected the fuses and I blew F804. I have since replaced the fuse and the lights work again. However, there is still no audio. I would be extremely grateful somebody could help me fix my receiver. Things to note: 1. I've noticed that when playing audio through an aux cord, with the volume turned all the way up, I can hear the beat of the music (or vibrations that sound like the music) in the power transformer. 2. I've noticed that the C813 capacitor gets very hot after the unit is on for ~5mins. 3. I've also noticed that the big, white R907 resistor gets hot as well. 4. When I turn the unit on, there is no relay *click* anymore. Any information would be greatly appreciated. I will gladly supply any other info/measurements that would be useful. I just need to get my hands on a multi-meter.

Please help!
 
Register to hide this ad
May have damaged (shorted) D803. That may be allowing AC voltage to get to C813 and also messing with the protect relay coil voltage. Use a 1N4004 diode if needed for D803.R907 will most likely normally run pretty warm. Thats why its a 5 watt resistor.

Welcome to AK Yamaha btw.
 
Last edited:
Okay, so I swapped D803 for a 1N4004. That solved the problem with C813 heating up. However there is still no sound. There is no relay *click* when the receiver is turned on. Something weird just happened though. I was messing with all the buttons and dials while playing audio through the auxiliary input. I turned the volume all the way up and the audio blasted from the speakers for half of a second until I lowered the volume all the way. After this incident I also noticed that the tuner's signal quality and FM Tuning dials are functioning again. Unfortunately, I am unable to re-create this "audio blast".
 
First look at the soldered connections of R907.Look for possible ring-cracks around the components leads.If no visble crack then...
Pull a lead of R907 loose and measure its resistance out of circuit.Looks like its suppose to be 180Ω +/- 10%.
 
Last edited:
OK need to measure the voltage on the base of TR901 or 902. Looking for near zero volts.
 
Also. How much DC voltage are you getting on both ends of R907.
 
To measure the above voltages. Clip your neg. test probe to the metal chassis. Then probe the components leads with the Pos probe. Wrap some tape or something around the pos.probes metal tip. Leaving just the very end exposed.Don't need any more oops incidents.:biggrin: Power on the unit. Then probe for the voltages requested at the various testing points.

Do you know how to identify the emitter,base and collector on a transistor?
 
Standard rule of thumb...When working around energized equipment. Always keep one hand in your pocket , so to speak.
 
Thanks for the tip! I stripped an old speaker wire of its insulation and slid that on the end of my probe. Worked like a charm :). I consulted google to learn how to identify the collector, base, and emitter. Here are the measurements (all measured for DC Voltage at the base/leads of the components):

R907: 26.6V (on both leads)

TR901: Collector: 0.001V || Base: 0.653V || Emitter: -1.015V

TR902: Collector: -0.614V || Base: -38.9V || Emitter: -1.019V

I hope this helps!
 
See if you can locate TR and TL test points. Need to measure the DC voltage at each one. Looking for near zero volts. TR and TL are located right behind TR904 as you are looking from the front.
Black probe chassis ground
Red probe to TR then to TL.
 
IT SPEAKS! I adjusted the DC Offset Voltage on VR701 and VR702 after I read about the two test points that you mentioned (in the measurements and adjustment section of the service manual). I have them both turned all the way to the left (if you are looking from the front).

Here are the test point readings after the adjustments:

TL: -1.95V
TR: 1.96V (***EDIT: this is positive, not negative.)

Are these readings okay? The receiver is fully functional right now! :beerchug:
 
Last edited:
I just read a comment from merrylander in a different thread (http://audiokarma.org/forums/index.php?threads/help-with-yamaha-cr-640.300606/) where he says:

"Using mini grabbers (Don't even think of using alligator clips) measure between a test point and the chassis. turn the variable resistor (slowly they can be twitchy as hell) until the offset is zero or as close as you can get.

Note: Volume control at zero and input selector to an empty input."

I have been turning the unit off, making adjustments, turning it on, and taking measurements; in that order. I'd imagine it'd be a lot easier if I use the method that merrylander mentioned. I also did not know that I needed to set the volume to zero and the input selector to an empty input. I will give that a try later and try to get the voltages as close to zero as possible. The only thing I am worried about is that my variable resistors are already turned all the way to the left. Doesn't this mean that I cannot turn the voltages down any further?
 
Last edited:
ChuckSunset said:
I just read a comment from merrylander in a different thread (http://audiokarma.org/forums/index.php?threads/help-with-yamaha-cr-640.300606/) where he says:

"Using mini grabbers (Don't even think of using alligator clips) measure between a test point and the chassis. turn the variable resistor (slowly they can be twitchy as hell) until the offset is zero or as close as you can get.

Note: Volume control at zero and input selector to an empty input."

I have been turning the unit off, making adjustments, turning it on, and taking measurements; in that order. I'd imagine it'd be a lot easier if I use the method that merrylander mentioned. I also did not know that I needed to set the volume to zero and the input selector to an empty input. I will give that a try later and try to get the voltages as close to zero as possible. The only thing I am worried about is that my variable resistors are already turned all the way to the left. Doesn't this mean that I cannot turn the voltages down any further?
Click to expand...
Preadjust both trimmers for the approx. center of there rotation..Just eyeball it.
 
basically what you are doing is setting the balance of the positive and negative voltages in that part of the circuit . ideally needs to be zero volts .a few millivolts is no problem . . then when the music is playing it can go negative and positive voltage pulling the speaker cones in and out and playing the music .
the zero voltage will be somewhere around the centre of travel on the adjustment pots .
 
Alright, I've got the DC Offset below 0.002V on each channel. Are there any other necessary things that I need to do to make sure the receiver is completely healthy?
 
You must log in or register to reply here.
Back
Top Bottom