petehall347
the brandy coffee man
whatever the resistor it is sure to be same value as the other channel resistor that does the same job .
Need help to identify resistor type and value on the power supply section of CR-840 receiver
- Thread starter doitnow
- Start date
Ok, I see what you guys were talking about the " other side/channel" now. I looked at the pre driver of the other IC 702 and the counterpart of the burned resistor's color band is orange, white, brown and gold so it is 390 ohms value.
Interesting thing is the other side is still using the OEM big 2 watts resistor as in the picture that clinic-audio provided. 2 questions please, should I leave them alone (the big resistors) or do I have to change them to the same type and ratings? And about the burned resistor, should I go for the metal film type or just carbon and stay with the 1/4 watt?
Sorry with all the basic questions, I am just a hobbyist so lots to learn from all you guys.
Interesting thing is the other side is still using the OEM big 2 watts resistor as in the picture that clinic-audio provided. 2 questions please, should I leave them alone (the big resistors) or do I have to change them to the same type and ratings? And about the burned resistor, should I go for the metal film type or just carbon and stay with the 1/4 watt?
Sorry with all the basic questions, I am just a hobbyist so lots to learn from all you guys.
R719 390Ω Carbon film. 1/4 watt
R717 390Ω metal oxide 2 watt
Last edited:
At 5% tolerance ( gold band )
Just replacing the resistors will probably result in the small (R719) burning up again. I'd be looking at IC701 very closely.
There is a possibility it is damaged.
Failure of the 390 ohm resistors indicates that one or more of the power pack emitter resistors failed first, which in turn means the power pack failed before that.
And the predriver will most likely have been damaged by the excessive current through the 390 ohm before it failed.
Sorry for the gloomy outlook, but I am quite sure it is accurate.
chazix
And the predriver will most likely have been damaged by the excessive current through the 390 ohm before it failed.
Sorry for the gloomy outlook, but I am quite sure it is accurate.
chazix
Update, purchased the 390 ohms today to replace the burned one and as soon as I turned the receiver on, the new one busted on flame.
So, the pre-driver IG 02940 (IC 701) is toasted ? Anything else that could have been damaged along the way?
Is there any equivalent modern IC that can replace it or I have to search for a used one from a part unit?
Any help is appreciated.
So, the pre-driver IG 02940 (IC 701) is toasted ? Anything else that could have been damaged along the way?
Is there any equivalent modern IC that can replace it or I have to search for a used one from a part unit?
Any help is appreciated.
Actually, IC701 is not the most certain to be toasted - though odds are that it is. What is certain is that the associated power pack and at least one of its emitter resistors (IC703, R721, and R723) have perished.
Both ICs are long out of production, with no contemporary equivalents being made by any mainstream manufacturer. You'll be able to find knock-offs. You might be able to get the power pack from a trusted supplier such as bdent.com - STK0080II is the part number to look for.
Pre-drivers are more likely to be offered under the Yamaha part number - but they definitely won't be parts made for Yamaha, and are probably more likely to be junk than the power packs. A "pull" pre-driver from a parts unit is probably at least as good a bet, if you can find such. At the risk of going commercial, I'll say that I can offer a hand-made reproduction pre-driver - PM me if you want info.
Chazix: I think I gonna have to this repair in the back burner for a few reasons, firstly, the Holiday season approaching that requires lot of time for gifts shopping, dinners planning and short trips here and there visiting friends and families. Second, this might be too much a repair for me to handle without the proper equipment to do all the testing and measuring and to hunt down obsolete parts and what not. Third, I do have another receiver that I can utilize for the time being so the urgency to get the Yamaha repair is quickly diminished.
Nevertheless, thank you for your time and I am sure your help will be needed when the time comes.
Thank you all that participated and Happy Holidays.
Nevertheless, thank you for your time and I am sure your help will be needed when the time comes.
Thank you all that participated and Happy Holidays.
One of the things I like about the vintage audio scene is that it's rare for anyone to be in an all-fired hurry
Happy Holidays!
