Ongoing saga of the Yamaha CR-n40s

Clinic,

Thank you for posting CR-840 schematic in post 96

And partial circuit diagram in 105.

The hifiengine service manual schematic wasn't very helpful to me and part numbers don't match part list (as far as I can tell).

I had googled and searched here for schematics but could not find them. Thus, in part I am posting this to help anyone who might search for CR840 or CR-840 schematic.
 
Hope I'm not being too chatty, but often in these threads there is no finale. Here is mine: listening to my CR-840 right now. SO HAPPY. I had a Technics SA-500 as a temp and just wasn't enjoying the music as much. I'm not discriminating enough to explain why, but much better with the Yamaha now (even playing on lesser speakers).

Thanks again, to you chazix, and all others who have posted helpful guidance in this thread.
 
Well, being rather chatty myself (in this thread, at least), let me say congratulations. Nice work!
 
Good evening how would I go about ordering one of your cr 1040 board drivers fixes and could you recommend anyone in San Diego that could troubleshoot and install it that you have dealt with. Thanks
 
Good evening how would I go about ordering one of your cr 1040 board drivers fixes and could you recommend anyone in San Diego that could troubleshoot and install it that you have dealt with.

Welcome to AK, Pat. I sent you a PM (aka "conversation"). Perhaps someone else will happen along here with a San Diego recommendation.
 
I think I have found someone on this thread who can help me do the troubleshooting to confirm 100 percent that I need your board and then I'm onboard with the purchase . Thanks very much
 
I'm going to concede defeat on my CR1040. I have lots and lots of parts i collected, new old stock and counterfeit PRE and outputs. 2 very nice faceplates and all switches and knobs, tuner and power. Once Chaziz tells me what he wants the rest is available. Mate, let me know what you'd like.
 
On-going saga indeed. Can someone please guide me a just a little with my CR-1040 troubleshooting?

Originally protection would stay on. IC604 (IG02960) was gone with that channel, along with one 0.47 Ohm resistor. I pulled that IC, and now relay engages, and Left channel plays fine.

The question is whether the driver IC IG02930 is ok or not in the Right channel.

I have not installed the resistors across the output IC connections. Without resistors here is what I am measuring on the driver ICs:

L(good) R
IC601 IC602
1 0.27 0.23
2 0 0
3 0.26 0.22
4 -49 -49
5 -50 -50
6 -50.6 -50.6
7 3.5 +50 ********
8 0.6 0.05
9 0 0
10 0.6 0.04
11 0.6 0.04
12 -7 dropping -50 **********
13 -2.5 -50 **********
14 3.9 50 *********
15 50.8 50.8

So I have pins 7, 12, 13, 14, which don't match. 7 and 14, 12 and 13 - just have a diode between them internally.


1) Just to confirm - which are the output pins of IC 601 / IC 602? 8 and 11? Doesn't seem right, as they are connected to transistor bases.

2) What is the purpose of connecting two resistors from pins 10 and 1 of IC 604 to a channel output (common point between two 0.47 Ohm resistors)? Someone mentioned a very similar case to mine, and that their voltages on pins 7-12-13-14 dropped significantly after they installed these two resistors for measurements purposes.

Thank you!
 
1) Just to confirm - which are the output pins of IC 601 / IC 602? 8 and 11? Doesn't seem right, as they are connected to transistor bases.

2) What is the purpose of connecting two resistors from pins 10 and 1 of IC 604 to a channel output (common point between two 0.47 Ohm resistors)?

Driver outputs are 13 and 14. 14 is meant to be a constant current source of about 6mA from the + supply. 13 is dynamic - depends very sensitively on the input (voltage difference between 1 and 3).

Tacking in those resistors is a way to close the overall feedback loop around the power amplifier circuit. Without that closure, voltage measurements are pretty much meaningless. With that closure, a functional driver should be able to stabilize the DC voltage at the amplifier output - and indeed, be able to produce audio output that's enough for headphones (only). Closing the loop is a good way, and AFAIK the only way, to make judgements about driver health in the absence of a power pack.

If an emitter resistor (the 0.47 ohm parts) opened up, it will very likely have damaged the secondary function of the driver, which is to detect and limit excessive current through the power pack. If the primary function of the driver (amplification) is still intact according to the closed-loop test, you can choose to ignore the loss of the current-limiting function, which IMO was never very effective to begin with. (BTW, it's likely there is also a toasted 390 ohm resistor if an emitter resistor opened up. But the 390 ohm parts only matter to the current-limiting function, so again you could choose to ignore them.)

HTH,

chazix
 
Both R632 and R634 are spot on 390 ohms and no burn marks on them, so they definitely survived, and 0.47 ohm R638 took the hit - measures at 120 ohms now.

I'll install the resistors, but having full power supply at pins 13 and 14 of the driver IC seems like a bad sign?
 
I'll install the resistors, but having full power supply at pins 13 and 14 of the driver IC seems like a bad sign?

Nope. Meaningless. Really. (Well, okay, actually it's sort of a good sign, in that it indicates that there is SOME path from those terminals to the power supply rails.)

The 390 ohm parts being OK is not evidence of anything, either, but it certainly isn't bad news.
 
Ok, installed 220 ohm resistors.

Pin 13 went to -1.6
Pin 14 went to 1.4

Pin 7 went to 25 and kept dropping.
Pin 12 went to -23 and kept dropping.

Connected headphones, and I have sound in both channels.

Does it mean my driver actually survived?

Thank you again.
 
Does it mean my driver actually survived?

Virtually 100% confidence that the amplification function is OK.

I can't say whether the current-limiting function is OK, but even if it is damaged, it is not damaged enough to interfere with amplification.

I'd suggest B&D (bdent.com) as a trustworthy source for a replacement power pack (STK0080II).
 
Thank you very much! I will order the Sanyo IC from there. (bdent is out of stock on STK0080II; I took my chances with ebay seller who sold 35 of these, hopefully they have a good part, not a garbage knockoff).
 
All current power packs are knockoffs by definition, but some are better than others. If this repair is for yourself, just test that the amplifier can survive at a level of output that is at the onset of clipping with an 8 ohm load. If it's for a client, better test with a 4 ohm load.
 
Hi folks-

I have an interesting version of this problem that I have not seen addressed - and am hoping one of you can provide guidance.
The problem is thermal drift in the offset of the a IG02940. Here's the sad tale:

(As context, I am a reasonably experienced amateur tech, having repaired/restored vintage gear for the past 15+ years.)

A friend brings me a Yamaha CR-840 complaining of sound quality issues. Sure enough, the left channel output shows a strange distortion when a sine wave is input (and one I have not seen before)- jagged "sawtooth" on the falling side (and only the falling side) of the sine wave at all reasonable levels. I swapped the left and right predrivers and the problem swapped with them, so ouala a bad IG02940. Lacking any alternative, I ordered a replacement on ebay from China, from the most promising sounding source I could find.

Three weeks later the part arrived. Slightly different package and VERY faint lettering, but whatever. Soldered it in, and ..... nothing. Complete brick. Took it out and checked various pins with an ohmeter. No chance it was a real 2940 (for example, diode drop between pins 1 and 4 has wrong polarity). Complained to supplier, who promised to send a replacement that "looked more like the original. Another three weeks pass and the replacement arrives. It does in fact look more like the original. And passes preliminary uninstalled checks. Installed, powered on, and within 15 seconds there is a loud, smoky 14 (between pins 7 & 8) has completely blown its can off and deposited threads of its internals all over the board. Wonderful. No more Chinese parts.

Was astonished to see a NOS IG02940 appear on ebay and snagged it. In the original Yamaha box with all legit markings, package looks great, long pins intact etc. The real deal. Installed it and, as a precaution, replaced all of the small electrolytics around it (C704, C708, C714, C716, and even C126) in case the bogus predriver had compromised them.

Now the problem: Initial measurements showed the infamous "pins 7, 8, and 10-14 all at 40+ volts". Rats. But as I watched, the situation changed. All of these slowly dropped into normal ranges. After about 15 minutes, everything looked more or less correct, with undistorted full amplitude outputs on pins 13 and 14. There is still significant offset at the junction of the power pak emitter resistors (a couple of volts) - but this is true on both channels so I am hoping this is operator error of some kind.

So something has major thermal drift. I hit the power pak with cool spray and nothing happened. Then I applied cool spray to the 2940 and within seconds it railed out again. Then, again, as it warmed up, the output reappeared and gradually sank to the proper range (centered near ground). So there is some kind of thermal issue with the predriver.

There is no obvious thermal compensation circuitry within the predriver or on the board. And I have been unable to find any mention of this problem on AK or elsewhere. I am really hoping that this miracle "last one on the planet" NOS part is not bad. Thanks in advance for any help!

By the way - the CR-840 service manual from hifiengine does not match this unit at all - different shsape amplifier board, different parts, etc. I found that the one for the CR-640 has the correct layout and schematics (and shows IG02940 and IG02970 as are in this unit).
 
Not likely. The problem presented itself before I thought to do the freeze spray test. I did check the impedance of the various components in the feedback loops. The trimmer measured as it should. (But strangely, even though each component tested good individually, the impedance between various pairs of pins of the predriver was not the same as on the good channel - not off by an order of magnitude, but off by more than 10%. I could never figure out why.)
 
A CR-840 was recently dropped off at my door by a friend seeking a dx and repair. So, I've been eye-balling the schematics for the last few days. First, it's been reported previously that the service manual for the CR-840 available on hifi engine has multiple errors. But the CR-640 and the CR-1040 service manuals are pretty good, although the latter has some data inconsistency issues. There is a decent CR-840 manual available for sale, but I have not purchased it yet until I establish my friend's budget for repair. Her gag price could be $0, who knows.

While the freely available CR-840 manual might be junk, it does include the schematic diagrams for the Yamaha proprietary IC's, the predriver IC IG02940 includes the functions of input stage, voltage amplification stage, and some sort of over-current crow bar protection scheme for the Power IC. The Power IC IG02970 includes the functions of the thermal bias stage and a triple EF follower output stage. So I wouldn't expect any sort of thermal compensation on the IPS and VAS stages, as I've never seen that in other discrete amp designs. But, that sure is an interesting finding you made. It makes me wonder if the timing of the relay protection circuit should not be redesigned for minutes rather than seconds.

Depending on the outcome of a cursory diagnostic inspection, my friend's budget, and the my confidence level of getting a working IG02940 IC off of ebay, my next call might be to bug user chazix for a schematic and BOM for the DIY module. I can make a board, and it would be an interesting project. But the originals mentioned by Merrylander have long disappeared from this thread.

Regards,

Rob
 
Back
Top Bottom