Yamaha M-70 Thread

I can't remember any audio project that I've done where I've made so many parts ordering mistakes as this one, especially concerning resistors.

So I opened my bag of 470 ohm resistors and I ordered... 10? Because I need 16? Well isn't that special.

Because I really don't want to go further without first testing the amp without OT's installed I'm going to have to wait until I can make another parts order next week. I have some other projects that need to be worked on in the waiting time.

Cheers,
James

I've missed parts in nearly every restore project I've done so far, especially resistors. The only reason I get away with it is ordering too many each project and having spares next time around.
This last project I made absolutely, positively sure I got everything. Triple checked and then checked once again before hitting ORDER. It was pretty good. I only missed one resistor value and two 22uf caps.
 
I've missed parts in nearly every restore project I've done so far, especially resistors. The only reason I get away with it is ordering too many each project and having spares next time around.
This last project I made absolutely, positively sure I got everything. Triple checked and then checked once again before hitting ORDER. It was pretty good. I only missed one resistor value and two 22uf caps.

Isn't this the truth. Well, I hope that I got it right this time. Ordered extras and some stuff for other projects, should be here by Saturday. One thing that I haven't ordered yet is LEDs for the panel lights because I haven't decided on exactly what yet. But I did find a 3.5v LED at work and figured out that a 470ohm resistor works with it with 12v input. I can at least use it as a temp lamp for the protection.

The Fluke 77 arrived yesterday and I took it to work today and compared it to a couple of other VOMs that we have there. Using 100, 1k and 100k resistors and 1N4148 diodes the 77 fell almost exactly nominal in it's readings, with the 2 work meters falling consistently 1 above and 1 below nominal readings. So it seems to check good. With this last Mouser order I bought a few 100ohm 0.1% tolerance resistors. I'll use them to do another check when they get here.

I made a decision concerning input jacks. I really like the stock ones on my CX-1. Solid brass and the cables that I have fit them nicely. There's a fellow in Hungary that sells a lot of Yamaha parts on ebay and I just bought 2 sets of the CX-1 jacks from him. I'll have to drill new mounting holes above/below but that's not a problem.

I still haven't decided on speaker posts. Can anyone explain to me the advantages (or not) of having rhodium plating on speaker posts?

Cheers,
James
 
You might want to consider a speaker post from the newer MX series amps. Used my extra MX-1000 post to my M-85 . It can now accept banana plugs. It is a direct fit.
 

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Can anyone explain to me the advantages (or not) of having rhodium plating on speaker posts?

You get to tell audiophile buddies (and us) that you run rhodium-plated speaker posts. :D

I'd just run whatever you think looks good and is functional for your purposes, don't think it matters a lot.
 
You might want to consider a speaker post from the newer MX series amps. Used my extra MX-1000 post to my M-85 . It can now accept banana plugs. It is a direct fit.

Good thought Edwin. I actually have a set of AX-750 posts here to repair one of those integrateds. Eyeball calibration says that they should fit the M-70 with a little work.

Cheers,
James
 
You get to tell audiophile buddies (and us) that you run rhodium-plated speaker posts. :D

I'd just run whatever you think looks good and is functional for your purposes, don't think it matters a lot.

Well, there is a lot to be said for bragging rights. :banana: But in the end of course you are right, it just has to work well.

I was just mildly curious is all. As to what the practical value is supposed to be. There's gotta be at least some theoretical reason for using it and I'm forever curious. That I would pay for them or not is another story. :)

Cheers,
James
 
The latest Mouser order arrived yesterday. I've come down with a cold so am moving a bit slow but still managed to get a little done today.

C151/33µF got pulled, it's holes cleaned of that gunk and re-installed.
The 470ohm bypass resistors got installed on the output TR pads.
And I temp mounted some driver TRs on small heat sinks and plugged them in.

DSC05145.jpg DSC05149.jpg

Cheers,
James
 
Left to do before I can turn it on is replacing the 2 0.01µF/250v safety caps on the power switch and removing the back panel so that I can get at the power cord strain relief to pull a bit more cord into the amp so that there is enough to properly solder the leads in place. If all goes well I'll do that tomorrow.

DSC05150.jpg DSC05152.jpg

Cheers,
James

edit: I bought Panasonic ECQ-U2A103ML, 275vac X2 caps for the switch.
https://www.mouser.de/ProductDetail...GAEpiMZZMv1cc3ydrPrF%2bfZ13WJ/r1/Npn8LbyFNYg=
 
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...and got the power cord re-attached. DSC05160.jpg DSC05162.jpg

And then I decided to find out what happens when I just try turning on the amp.

And what happens is that it instantly trips the 16A breaker for the room. But it doesn't blow any fuses in the amp. Now, I've read HypnoToad's thread concerning this...
http://www.audiokarma.org/forums/index.php?threads/yamaha-m-70-tripping-circuit-breaker.451385/

...and I'm hoping that I'm just dealing with too much inrush current tripping the breaker.

So, 2 thoughts now. I may have to re-evaluate those increased capacity filter caps. I do have some UCC KMH in 18000µF/80v on hand, so changing the caps in the high power section back to the stock rating won't be a big deal. And, one of the guys at work was slaughtering an old piece of test equipment in prep for recycling and he found and saved an old sliding transformer for me. 0-240v 4.5A. I'll have to come up with a box and connection plugs etc but I can build a variac with it.

I'm home sick with a cold this week, and on vacation next week, so it will be a couple of weeks to get that project moving but it seems to be the best way forward at this point.

Cheers,
James
 
Well, measuring the AX-750 speaker posts they do not fit, vertical spacing is too tall on the AX posts.

And the CX-1 input jacks arrived. Too bad that I didn't think to measure their spacing on my CX-1 because they are also a bit too far apart and won't fit the M-70.

So back to square 1 on both of these.

Cheers,
James
 
I made a Mouser order for a different project and decided to throw in some UCC KMH 10000µF/80v caps.
https://www.mouser.de/ProductDetail...GAEpiMZZMtZ1n0r9vR22RSFeKT/CuZ6%2bTXe5TLUhmE=

I figured that if I'm going to reduce the filter caps in the high power section I might as well do both sections. The order arrived today and so I swapped all 4 caps. Now they are all at the stock values, except that the small ones are 80v. The 10000µF/80v actually have a higher ripple current rating than the 12000µF/63v, 4.77 vs 4.01.

I haven't as yet attempted to turn on the amp with the "reduced capacity" caps.

Cheers,
James
 
Looking very good, l hope the circuit breaker problem is just something simple. I have been looking forward to your progress on your project but for some reason l haven't been receiving alerts for your thread. Will be keeping a close eye on it now :thumbsup:.
 
Looking very good, l hope the circuit breaker problem is just something simple. I have been looking forward to your progress on your project but for some reason l haven't been receiving alerts for your thread. Will be keeping a close eye on it now :thumbsup:.

Thanks! For my part I hope that it's something simple also, but my luck sometimes runs otherwise.

In the meantime I found and bought a 2000w/230v variac for €75. It has a voltmeter, protection, etc. For that price, considering that I would have to find/make a case, connections, fuses, meter for the bare trafo that my friend found, well, I just went ahead and bought it. I also bought an inexpensive 30vdc bench power supply. I'll be using it to test some assorted LEDs that I bought as lamp replacements.

I've noticed lately that sometimes watched threads don't give me alerts. Once I've manually re-accessed the thread in question the alerts start again. ??

Cheers,
James
 
Sounds like you have picked up some very handy gear, i'm sure they will come in useful. Oh o.k so l am not the only one having issues with alerts, hopefully all good now.
 
OK. So I believe that I found my problem. Or to be more exact I definitely found a problem, 2 in fact, and they are self made. I'm hoping that they are THE problem.

The last 2 days were spent rechecking everything that I've done so far. Looking for solder bridges (none), parts installed backwards (kinda, 2), and reviewing datasheets.

Short answer, I did something dumb.

Long answer, SCR601 and SCR602. While the subs that I bought and used are reasonably good spec wise I failed to check their pin-outs and they are both different that the originals. SCR603 checked good. The real dumb thing is that they are the only 3 parts that I didn't check the pin-outs on.

SCR601 = SFOR3G42 has 1=Gate, 2=Anode, 3=Cathode. My replacement S4X8ES has Cathode, Gate, Anode.
SCR602 = SMOR5G42 has 1=Gate, 2=T2, 3=T1. My replacement LX807DE has T1, Gate, T2.

So I had to reverse the positions of pins 2 and 3 and then install them backwards/180° to the original.

So far I haven't found anything else that is wrong. Tomorrow I'll try turning it on again.

Cheers,
James
 
Hopefully that sorts it out for you.
I skipped back to find out what those were, any reason you didn't just leave the original parts if they tested okay? Just didn't trust them?

Also, did you find some terminals you like?

Sounds like it's getting pretty close anyway!
Those KMH caps always look real nice in your builds too.
 
Hopefully that sorts it out for you.
I skipped back to find out what those were, any reason you didn't just leave the original parts if they tested okay? Just didn't trust them?

Also, did you find some terminals you like?

Sounds like it's getting pretty close anyway!
Those KMH caps always look real nice in your builds too.

I did not trust them, and I somewhat dislike re-installing parts that are old with unknown old stress, as well as heat stress from several amounts of soldering. But I still have the old ones as a last chance backup.

I haven't decided on terminals yet. I have a few in mind on the short list and will decide after I'm at least at the point where the amp will start. And I still haven't discovered what the magical properties of rhodium plating are. :)

The UCC KMH caps have been making me happy, especially their pin compatibility with so many Yamaha amps.

I'm hoping that the variac arrives tomorrow.

In another direction, with my last Mouser order I bought some LEDs to test for the power/protection and meter backlight lamps. When the 30v PSU gets here I'll do some mock-ups and test them.
60° round top for the power/protection and 100° straw-hat for the meter backlight...
https://www.mouser.de/ProductDetail...hhHz6G0OHRHNprYehaM8LNMtZrZ1xQgLcpKy/McNZRA==
https://www.mouser.de/ProductDetail...hhHz6G0OHRNWXbU28CFBoHjLorRU5F2ppQPGasDDgfA==

Cheers,
James
 
Sounds like you have picked up some very handy gear, i'm sure they will come in useful. Oh o.k so l am not the only one having issues with alerts, hopefully all good now.

Working on it. Next on the list of tools to buy is an oscilloscope. Hopefully in the next few months.

Cheers,
James
 
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