Ongoing saga of the Yamaha CR-n40s

merrylander

AK Member
After cutting the cover from an original Yamaha IG02930 pre-driver chip, finding Sanyo’s recommended circuit, and checking the schematic in the CR-1040 service manual that showed what was internal to the IG02930, I was able to come up with the schematic for a replacement.

The IG02930 is basically Sanyo’s circuit with some added components. It was relatively easy to determine resistance values with a meter on the un-covered IG02930. Diodes and transistors were taken from typical devices that would meet the voltages in a CR-1040. Since the internals of all pre-drivers are the same with only different voltage ratings, this replacement will sub for IG02940 and IG02950, in other words it will work in the CR-840 and CR-640.

Although I also did a drawing for a circuit board I was not about to order up a batch until I had proven my circuit. At Radio Shack I found some small circuit boards that had 15 row and 15 columns, just the thing for a 15-pin device. This is shown in the third drawing, not pretty, but effective. This layout took a few tries and is the way it is simply because I found you could not get two component leads through a single hole. I also laid it out so that the three legs of each transistor would bend to the corners of an equilateral triangle and not be crossing each other.

If you choose to construct a pair of these devices I suggest that you mount the components first and just tack them in place with a bit of solder. Next run all the surface wiring and lastly get some Kynar wire run the insulated leads. I strongly suggest that you do not attempt to do it all in one pass or you will need the services of a good Ophthalmologist. Don’t cut any surplus wire from the components until step 2 as this extra lead will form the surface wiring in many cases.

I downloaded the free copy of Eagle but the learning curve looks to need more time than I have spare. One could make a single circuit board large enough to comfortably hold the components of both pre-drivers and simply hook that into the main PC board with ribbon cables. That, or translate the transistors into surface mount equivalents and do a small board.
 
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This is what the inside of the hybrid looks like, TR06 is usually the one to blow. Note that although Yamaha gave three numbers for these pre-drivers they all used the same circuit, it was only their voltage limits that differentiated the IG02930 from the IG02940 and the IG02950. I selected components in the previous post that would tolerate the voltages of the CR-1040 so they will be quite at home in the CR-840 and CR-640.
 
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that is gorgeous Merrylander. I assume you are thinking of making a pcb to sell? Would you add my name to your files to contact when you have them ready please?
 
Nope, if anyone wants to take the schematic and let Eagle draw up a PC board be my guest. There is an AK member with a CR-1040 that may have a sick pre-driver, t'would be a good idea to let him try the mockup and see if I got it all correct before anyone goes the PC board route.
 
If you know its TR06 thats blown on the Yamaha module couldn't you remove the cover as you have done and solder in place the discrete equivelant?
This may be a stupid question but it would seem to be easier than building the whole board.
 
Doc is correct about the connections inside being welded. If you enlarge the photo in post #2 TR06 is the bigger whitish square top slightly right of center. This is the actual die you might find inside a regular discrete transistor and the die itself is welded to one trace whilst the two other leads are spot welded to the other traces. The surface mount caps are fairly obvious, the resistors are the black blobs like the one to the right of TR06.

But the thought occured to me as well, would not have looked much funnier than the pre-driver I built on the RS perf board.
 
Could this be worked on the X module?

Hi Merrylander,

I have an R-2000 that I think has a bad X module. Could we open one up and "clone" it as you've done here with the predriver? Have you ever opened up an X module? Just wondering.

Thanks,
John
 
Probably not but I do have an R-2000 sitting on the shelf that needs the STK3156 but I think the power X module is OK.
 
i don't think you can solder to the stuff inside. Most connections are welded.

Thanks Nakdoc. I was pretty sure someone had tried that by now. Probably take a pretty sophisticated pressure activated welder to replace those.
 
Hello Rob, I just bought a CR-1040 that was not working...no sound and no protection relay engaging. I got it home, ran the voltage tests on the Pre driver hybrid as you described in another thread, then removed the power amp and rechecked the voltages.....same thing, high DC voltages on the 13 and 14 pin. After reading some other threads about the CR-1040 with this problem, I have to wonder how many one channel CR-1040's are sitting in limbo? I don't want to trash this unit but would rather hold out for a miracle I guess to find a solution. Did you ever test your mock up board? I would consider making one if I thought it would work. Any thoughts....suggestions?
Joe
 
Joe,

PM me with an address, I have one board made up but no chance to test it. If you want to be adventurous I'll mail it to you.

Rob
 
Hello Rob,

I made one of your pre-driver clones last weekend for a CR-840. The output module was blown and has been removed. After installing my clone, pins 13 and 14 still read 40+ volts. I double checked the circuit quite carefully before installing it, but must have missed something. Is it correct that without the output module installed these voltages should still read about +/-3V? If my predriver is in fact correct, what other items in the surrounding circuitry might cause this?

Thanks,
John
 
Pins 13 and 14 are the outputs to the power amp module so if neithet module is present there should be no voltage present. As to missing something I might well have done that myself, wiring that thing on that RS board was a real PITA.
 
Hi Rob,

Thought I would pass along this bit of info. The other night after pondering for a while about the elevated output voltages at the predriver, I desoldered and removed the power output module from the good channel. With the stk power module out of the amp, pins 13 & 14 of the good predriver were at about +/-45V. This makes me believe that this isn't necessarily a complete test for the predrivers. My DIY predriver output pins are about the same 45V with no load on them. I think I'll plug in the new power module when it arrives and see if I get smoke.

Thanks again for posting your great info about the predriver circuit.

John
 
Is there a simple meter test (out of circuit)that can be done to eliminate the main power amp module as the source of the problem. I guess I could unsolder the power amp module on the good side, compare the meter readings to the power amp module on the suspect side, then maybe install it on the suspect side and see what happens. That would definitely eliminate the power amp module as the source of the problem. I don't really want to heat any parts more than I have to as the heat alone could ruin a component. The power amp module was fairly easy to remove and I would take a chance removing the other one if this is a viable test option. Is there an out of circuit meter test I can do on the power amp module to eliminate it as the problem. On my unit, when I removed the power amp module on the suspect side, the protection circuit engaged when I powered the unit up. It did not do it before. My readings on pins 13 & 14 on the suspect side were exactly as Rob said....49+VDC.
At the same time fellas I don't was to destroy any other good components by mucking about on the board. I would rather be over analytical than ruin something else along the way....then I would have 2 or three problems instead of 1. Nerdorama, did you do any meter testing on your power amp modules or was yours just fried? Thanks fellas....Joe
 
Hi Joe,

One quick check you can make is measure resistance between output module pins 2-3 and 9-8. 2/9 are the output transistor collectors and 3/8 the emitter pins. It they are shorted or low resistance you will know the outputs are fried and you wouldn't have to remove the module from the board to wee this. This was the case with my bad channel. Once I removed the bad output module, the protection relay pulled in the the other channel worked.

Good luck,
John
 
John, I have already removed the O/P module (heat sink ass'y) on the suspect side (channel) of the board. I powered up and the relay clicked in. I did not have a source chosen so didn't check for an audible. I will go back and do that. The same criteria should apply for the readings between Emitter and Collector whether attached to the board or not right? If right.....then I'll compare the suspect power mod readings to the the good one (which will still be attached to the board). Like you said thought either a short or a low reading means trouble. If I get high readings then I should be able to compare these readings to the good one and if the suspect one is good then the readings should be the same (even if one is on the board and the other is not)?
 
Gentlemen, I just checked the resistance between pins 2-3 and 8-9 on both mods (one in circuit, one out). The one in circuit (good one) had high resistance (showed over 60 on the 200k setting) both ways. The suspect channel one (removed) showed about 40 ohms between 8-9 and open between pins 2-3. Again, these readings were taken with one mod out of circuit and the other one in. What do you think?
 
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