Ongoing saga of the Yamaha CR-n40s

Summary of issues spanning the last few pages and posts #167 - #226

I sincerely hope this helps some one else get one of these going again!

1. Purchased CR1040 with non standard STK0080 power amp repair, non standard resistor (R635/R637) causing distortion and clipping in left channel.
2. All lamps are blown. Install new lamps.
3. Blown power circuit (Fuse F702/diode D701) by accidentally shorting the power wire to the tuner board lights.
4. Obtained ebay ST0080II (it doesnt work at all)
5. Obtained STK0080II from utsource and installed
6. Installed incorrect resistor (R635/R637) to replace the non standard/shorted resistor (i installed 470ohm, should be .47ohm as advised by Chazix. :nono: :(
7. Installed correct resistors and adjusted DC offset = amp sounding great.

8. Massive pop in speakers on power on, protection relay is instant on. No delay between hitting power button and the relay click.
9. Replace D805 with 1N4004
10. Amp now powers on gracefully and silnetly with 4 sec delay.

Working beautifully!!! All thanks to the patience and skills of CHAZIX!
 
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Hi!

I have one CR-840 to fix that is my friend's. It has one bad driver IG02940. Fortunately I checked the ebay one last time before telling the friend that you have now only one channel because no spare is available. So I ordered two from hkutsource. Don't know what to expect but me and the friend knows risk about counterfeit stuff. I let you know when I get them.

Symptoms where that protection circuit stopped speaker relay to switch and measuring DC offset showed that one channel was out of line and couldn't be trimmed near zero DC. Then I took driver IC from bad channel off and protection circuit didn't kick in and that channel worked fine. I took the working driver and swapped it to bad channel and that worked too now. So I think all other components including finals are OK.

If those hkutsource spares are bad I would like to know schematic and PCB screen if someone can provide those. I have etching stuff and boards so I can do it myself. However if this is against designers will I respect that.

Thanks for everyone sharing this info in this forum because this is vital to keep these nice machines working :) Cheers from Finland!
 
Hei, swataia,

I can tell you that I purchased parts called IG02950 (the pre-driver from the CR-640) from the same ebay seller, and was satisfied with them. The parts I received were newly manufactured reproductions of the Yamaha part.

I hope you will have the same luck with IG02940 replacements, but if it turns out that you need the schematic, I can find the one that Merrylander produced. (I am sure it has already been posted in this thread, but I think image file attachments expire after some period.)

Cheers,

chazix
 
Hi chazix!

Yeah, I received them two days ago and tried them. Both not working :( Bad luck then, they just heat up and there is huge DC offset in amp output stage. I contacted seller to see what we can do. Maybe its better to build this from Merrylanders schematic. If you can, please PM it to me :)

Those that I received were used parts, they had old solder in pins. However sold as "working".

I'm going to change the working pre-driver to other channel again to check these didn't blow up the output stage...
 
Sorry to hear that you got bad parts, swataia.

I don't see a way to put attachments into PMs, so I'll post Merrylander's schematic here. It is a scan from a paper copy, with some hand marking that I made. Sorry about the quality.

I believe the passive part values to be accurate. I haven't really reviewed the suggested semiconductors. If you decide to build the circuit, you might want to make your own choices of semiconductors that you can obtain locally. Note that R3 dissipates nearly 1/2 watt, and the output transistors TR6 and TR9 around 1/3 watt.

Cheers,

chazix
 

Attachments

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hello to all,
bit late on this thread,but I also purchased two pre-drivers from utsource,both of those were also duff,so would not recommend this seller here!.
On opening the rather obvious fake,I did notice a burnt thinfilm resistor,just to the right of top-centre.mmm...
 
I've gotten at least one acceptable IG02950-marked part from UTsource myself. So, it seems like it's a hit or miss kind of thing.

chazix
 
Hello all,

New to AK. I recently purchased a Yahama CR-840 and I would like to avoid these seemingly devastating pre-driver issues.

Would a cooling fan placed externally on top of the unit be enough to prevent the pre-driver problem or is the "heatsink installation method" the best way to prevent the problem.

I have very little technical electronics experience. If the heatsink method is the way to go, is this something that I could do myself with a tutorial? Or, since I do have a local pc/electronics repairman that I use, should I just bring it to him to install the heatsink(s)?

The information on this thread has been very helpful so far. Thanks for any other assistance offered. Also, I'm not in a rush... I want to get this right from the start.

Christopher.
 
I don't have an informed opinion about heat sink vs. fan, but around post #60 in this labyrinthine thread there is detailed info on
4seatPilot's heat sink project, with pictures.

Cheers,

chazix
 
I don't have an informed opinion about heat sink vs. fan, but around post #60 in this labyrinthine thread there is detailed info on
4seatPilot's heat sink project, with pictures.

Cheers,

chazix

Thanks for the quick response. I think with my limited skills, I will bring the 840 to my tech guy and show him 4seatpilot's pics and description and let him try it.
 
Anyone know of any repairers in Australia? My CR1040 is unwell and beyond my skills to repair - despite the ultra patient and persistent and skilled support of Chazix - i cant get it going and some of the pads are starting to lift from so much soldering. It really needs some expertise. I have tons of New parts (eg the IC Pre and STKs) but it has other issues.

I really like this thing but i dont want to 'fix it to death'. If i cant find a repairer of these out here i will pull it apart and sell the bits (i doubt anyone will want a project).
 
Anyone know of any repairers in Australia? My CR1040 is unwell and beyond my skills to repair - despite the ultra patient and persistent and skilled support of Chazix - i cant get it going and some of the pads are starting to lift from so much soldering. It really needs some expertise. I have tons of New parts (eg the IC Pre and STKs) but it has other issues.

I really like this thing but i dont want to 'fix it to death'. If i cant find a repairer of these out here i will pull it apart and sell the bits (i doubt anyone will want a project).
If I lived down under id give it a shot . Too bad I hope you find some one.

Nashou
 
Chazix, I wonder if you would have time to render what I hope would be for you a quick opinion/advice that might help save a CR-840.

A short of left speaker wires lead to relay not engaging. A visit to shop didn't help (long story, will skip that).

Today I pulled the left output amp (was a 00600II) and tack soldered the resistors as per early in this thread. Right side output remains in place at it is a 02970. (My thinking was (and I'm beginning apprentice level in terms of my knowledge and skills) that because voltage was not too high in 13 and 14, -1.6 and 4.4 V, problem maybe not pre driver, and at pins 10 and 11 reading of 1.4V each maybe indicated shorted/defective output IC.) No indication of burnt resistors.

Anyway, relay's now click, I have adjusted DC under 10 mV on both channels, and I can listen to radio over headphones.

Should I be able to install new STK 0060II at this point? Should I replace the four white resistors, 2 at 4.7 ohm , and 2 at 0.47 ohm (I don't know part number because my board doesn't match manual) as well? Are those the emitter resistors? Anything else I should check?

Readings at the pre driver pins are (pin, V L, V R):

1 .2 .2
2 -1mv -1mv
3 -.2 -.2
4 46 46
5 46 46
6 48 47
7 -3.1 -1.1
8 -16mv 8mv
9 0 0
10 1mv 5mv
11 20 mv 4 mv
12 2.9 1.1
13 3.3 1.4
14 -3.4 -1.4
15 48 48

Thank you, and all who have contributed to this great thread.

Edit: I measured across the two 220 ohm resistors and get 1.5 V and -1.5 V
 
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Anyway, relay's now click, I have adjusted DC under 10 mV on both channels, and I can listen to radio over headphones.
I think this is sufficient evidence that your predrivers are OK.

There should be a total of four 0.47 ohm ceramic resistors in the vicinity of the output power packs (two resistors per pack, connected to the emitter pins, 3 and 8). If there are really some 4.7 ohm parts present, I think they were mistakenly installed. In your circumstance, I don't think it's crucial to replace the 0.47 ohm parts if they measure OK on an ohmmeter. But the emitter resistors should definitely all be 0.47 ohms, so replace any that are not of that value.

Cheers,

chazix
 
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