Ongoing saga of the Yamaha CR-n40s

I would add that the pin4 voltage is also wrong.

Also questioning the voltage on pin7. Look at resistance measurement of pin7 - 11K when it should be > 1M. Perhaps the external capacitor between pin7 and pin8 is the source of the 11K resistance leading to the 19.4V instead of the 4.3V on pin7.

I agree, resistance and voltage readings (meaning internal diode drops) both indicate that power IC is good.

So, either external pin7 to pin8 cap is bad, or predriver IC is bad.

ps. The resistance measurements were made to verify that their were no open traces.
 
In my view, regardless of what's going on with pin 7, it doesn't affect the conclusion that the voltage readings on pin 3 & 5 indicate that the predriver is no good. (I understand that it might be hard to accept that conclusion, since the part was just replaced. Nevertheless...)

Side notes:

I don't think I can take the time right now to explain the functional role of pin 7, but it is associated with a secondary function of the predriver (to sense current in the output module and try to limit that current if it's excessive), and not with the primary function of the predriver (voltage amplification).

If the capacitor connected to pin 7 was leaky, the worst that would happen would be that the amplifier's ability to drive positive-going signals would be limited. At idle, it wouldn't matter - the predriver's primary function would still act to maintain the amplifier's output at zero DC volts.

chazix
 
@kenwood61 I had done the chinese ebay seller mentioned much farther back in this thread, and the end result was 2 dead pre drivers, for the price i didnt bother to give feed back i will do so now. Lucky for me as it turns out there was something else wrong on the board and my original pre driver was actually OK! (on a CR 640)
 
I agree pin7 is not in the direct signal path, or is it?

In the schematic of the predriver IC (from the CR-1040 service manual), pin 7 is one diode drop lower than pin14. Also, pin12 is one diode drop higher than pin13. But Matt's measurements never show this link. So does diode exist between 7 and 14, or has it been destroyed?

Let's say diode between the two pins is highly resistive (> 10K). then could pin14 be at +40v while pin7 is at +17v? Could voltage on pin7 be forcing a higher voltage on pin 14. Remember we are expecting +3v on pin14. Or is the +40v on pin14 forcing the voltage on pin7 via the resistive forward diode between the two.

Nevertheless, I also conclude predriver IC must be broken as indicated by the voltages measured on pins 4,5,and 6.
 
UTsource is where I picked up the 2 i had. The guy working on mine said both were bad, but we were fortunate to have a different problem on the board that was making the predriver look bad, sounds familiar hey ;-)

I wonder if i might get him to help me understand what he found, as it may apply here.
 
So, it may be obvious that I like this series of receivers. So much that I recently got one towards the low end, a CR-440. There wasn't much wrong with it, but I did some surfing for info and pulled a manual from hifiengine anyway. Elsewhere in audiokarma, I noticed that there might be a misconception about the architecture of the power amp stage in this model, so I thought I'd put a note here.

The CR-440 does NOT use separate predriver and power modules like the higher-numbered CR-n40s. Rather, the IG02990 used in the 440 is a complete power op amp in one module. It can't be replaced by any of the Darlington power packs in the STK series. It's probable that STK084 will do the trick, and I think they can still be sourced. The pinouts, form factor, and essential function are the same, including the same layout of frequency-response-determining parts. The main difference I see in the internals of the IG02990 and STK084 is that the former has a fully complementary output stage, while the latter is "quasi-complementary". Might make a difference in that last fractional percentage of harmonic distortion spec, but probably not too big a deal in the grand scheme of things.

Something that puzzles me: neither the IG02990 nor STK08n series has any provision for emitter resistors. Is the bias network so thermally well-coupled that there's no chance of thermal runaway? Really??

Cheers,

chazix
 
Merrylander's schematic is correct, to my knowledge. Except for the red part, it's what I use in reproduction modules.

(The red part constitutes a current-limiting function for the output stage. In normal operation, it doesn't do anything. Given that output stages fail so often, I suspect that the red circuitry doesn't do much in an overload condition, either. I suspect that, at the least, it operates too slowly. In reproduction modules, I replace the red part of the circuit with a similar design cribbed from Marantz 6000.)

chazix
 
Hello all, just joined after doing a repair on my 30 year old CR-840. Back then I replaced the predriver, only to have it die somewhat later. I kept the receiver figuring I would repair it someday.........

Anyway, got to looking at it recently and the predriver is dead again....reading this board, Yamaha seems to have issues with their design, plus predrivers are not available...

So I decided to do an end run, got a TI (National semi) LM3876 IC amplifier, it'll do 56 W correctly heatsunk and seems to be a good match for the supply rails in the 840. It needs 7 external components, (3 resistors, 4 electrolytic caps) and you are done. Took out the predriver and final amp, wired the new amp to the signal input of the old predriver, output to the previous output point, mounted on a good heat sink, and it's back in business.

For those who want to get their 840 working again, this is a simpler solution in my mind compared to duplicating the predriver circuit.

Speaker protection works normally, too. Next I need to replace some of the front panel lights with LEDS.

George
 
Latest info on hard to find Driver and output modules for Yamaha CR-1040.

I had repaired one of my units last summer using A STK0080 Type II for the output module, to replace defective IG02970. I also located (reasonably priced online) Yamaha IG02950's to replace a bad IG02940. I purchased the IG02950 from utsource.net
I just went in to verify the availability, and they now stock almost all of the hard to find modules. They have IG02940, IG02950, IG02970, IG02980, and IG03000 and others. They are I assume manufactured in China, and sold out of Singapore. They are all marked Yamaha and are priced from $8 to $12 per. While I have found the STK0080 Type II, and STK0100 Type II to be great replacements for the output module, UTsource is the only place I have found the drivers.
 
Tom B mentions CR-1040, but seems to be describing the CR-840 module set?

Also, installing IG02950 (CR-640 predriver) in place of IG02940 (CR-840 predriver) is risky. If we assume that they really were different modules, the IG02950 might not be able to withstand the full signal voltage swings that an IG02940 can. For receivers that aren't ever going to be pushed to near their maximum output, it probably doesn't matter if you make that substitution.

If anyone does need safe, drop-in replacements for CR-1040 or CR-840 predrivers, you can find my pitch for repro modules in BarterTown.

Cheers,

chazix
 
Georgia Audio Labs had a couple of the power paks in stock for my CR-840. $20 a piece, and even with cheap shipping, they came in three days. Good deal. Got the only two they had at this time anyway. Popped em in and changed a couple of ugly looking filter caps, and she's humming away again. My CR-440 wasn't quite cutting it as a sub.
 
Hi, Mr.Texas,

My predriver repros will work in a CR-640. Feel free to PM me if you want to go that way.

At the risk of cheating myself out of some "business", though: A while back, I picked up what was billed as an IG02950 from hkutsource on that auction site, and ran it successfully through the same tests I run on my repros (except using the power supply voltages found in the CR-640). It's not very likely that it's a real Yamaha part, and I suppose it's possible that you'll get something different than I did, but I was satisfied with the part I got.

(I would *NOT* deal with the other outfit that's currently claiming to offer IG02950, "u-barn". They couldn't even be troubled to gin up a plausible picture for their listing, so they stole a picture of my repro instead.)

Cheers,

chazix
 
Chazix,

I picked up a couple from Hkutsource but it turns out my pre drives were ok (there was some problem just before them ) so i sent one (or two) to Merrylander, I do not know if he has had the chance to install it in his hopefully former doorstop :)

Hopefully he will have a chance to try it out and let us know. that said .. i found a 2040 that seems to be drawing my affection away from the 640 and its now just sitting on a shelf .. all purrdy
 
This kind of pretty?

IMGP0314.jpg
 
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