Yamaha B2~ Should I repair the input board or do the bypass modification?

Very nice work Cinic! Thanks for posting the pictures. Both of my B-2's are misbehaving right now because of those nasty switches; it's very annoying and because I've only ever had one source connected to it/them and I've never change the attenuator settings since I've owned them I'm thinking I'm going to add some jumpers to that board soon to remedy the problem. They can always be remove later if new switches become available. :thumbsup:
The switches are not that hard to clean. Not too hard to get to, either.
Once cleaned there will be no measurable resistance.
The pots clean out well too. No need to replace them either.
 
The switches are not that hard to clean. Not too hard to get to, either.
Yes indeed. The switches/pots have been cleaned several times over the years and work well for a couple of years ... but then the problem returns. :thumbsdown:
 
Go for direct input from one set of RCA's to the driver boards and all your problems (related to those switches) will be gone :bigok: I think it can be considered a proven concept. I cleaned them anyway, but bypassed them and I'm very happy with it.
 
Go for direct input from one set of RCA's to the driver boards and all your problems (related to those switches) will be gone :bigok: I think it can be considered a proven concept. I cleaned them anyway, but bypassed them and I'm very happy with it.

The minimalist in me loves this approach. The less in the signal path, the better. :rockon:
 
Yes indeed. The switches/pots have been cleaned several times over the years and work well for a couple of years ... but then the problem returns. :thumbsdown:
Aggh, sorry to hear that.
Maybe new switches become available.

Bypassing works for me as long as is reversible.
 
Yes indeed. The switches/pots have been cleaned several times over the years and work well for a couple of years ... but then the problem returns. :thumbsdown:


Use Stabilant22 after cleaning to protect from Oxidation and make a better electrical contact.

I use it on all connectors for any electronic gear i work on or repair. Even in my automobiles and compressor equipment at my restaurant.
My refrigeration guy is baffled why my relays and defrost timers seem to last forever compared to his other clients. I never tell him my secrete . ;)

Athanasios
 
Go for direct input from one set of RCA's to the driver boards and all your problems (related to those switches) will be gone :bigok: I think it can be considered a proven concept. I cleaned them anyway, but bypassed them and I'm very happy with it.

If doing this mod, take note of what has been addressed about the missing 0V return loop if you do that without further knowledge.
hence, do take care of it

http://audiokarma.org/forums/index.php?threads/yamaha-b2-input-switch-attenuator-bypass.754945/
 
If doing this mod, take note of what has been addressed about the missing 0V return loop if you do that without further knowledge.
hence, do take care of it

http://audiokarma.org/forums/index.php?threads/yamaha-b2-input-switch-attenuator-bypass.754945/


Id like to do this mod just to get listening to the amp while I design the new boards eventually .

Id like to use one of the existing inputs and not drill any holes in to the amp for any new RCA's .
Is this possible? I have not looked close to the rear input board yet. But I am sure it can be done some how.

So I think I'll go direct , change out R101 to 100kohm and add the ground from 0 to E on the Cap board.

All this, of course, after i check out the main caps and some other things.

What about those dual diodes that other Yammies and Sony's have that if they fail can kill the output devices , Are these relevant here ?

I read somewhere they these are not the same diodes that you replace with in series 1N4148's ( right part number?)

Athanasios
 
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Use Stabilant22 after cleaning to protect from Oxidation and make a better electrical contact.

I use it on all connectors for any electronic gear i work on or repair. Even in my automobiles and compressor equipment at my restaurant.
My refrigeration guy is baffled why my relays and defrost timers seem to last forever compared to his other clients. I never tell him my secrete . ;)

Athanasios
I will try that. I usually leave the contacts sprayed with feather lube after I physically clean them. Same for the pots.
 
Id like to do this mod just to get listening to the amp while I design the new boards eventually .

Id like to use one of the existing inputs and not drill any holes in to the amp for any new RCA's .
Is this possible? I have not looked close tot he rear input board yet. But I am sure it can be done some how.

So I think I'll go direct , change out R101 to 100kohm and add the ground from 0 to E on the Cap board.

All this, of course, after i check out the main caps and some other things.

What about those dual diodes that other Yammies and Sony's have that if they fail can kill the output devices , Are these relevant here ?

I read somewhere they these are not the same diodes that you replace with in series 1N4148's ( right part number?)

Athanasios
You can add proper RCA's without drilling holes. Just unsolder the plactic plate with the stock RCA's from the input board and mount some nice RCA sockets in the existing holes. Pick sockets that do not go deep in the holes, so that the input board can be put back in place. Note: Input 2 has no function because of the direct input mod, just for looks.

I would change R101 to 150K and J102 to 1,5K on both driver boards. And don't forget to use shielded wire from RCA to the driver boards.

About the varistors: there are a lot of opinions on that. I replaced all with two 1N4148's in series to be sure.

IMG_3462.JPG

IMG_3774.JPG

IMG_3775.JPG
 
You can add proper RCA's without drilling holes. Just unsolder the plactic plate with the stock RCA's from the input board and mount some nice RCA sockets in the existing holes. Pick sockets that do not go deep in the holes, so that the input board can be put back in place. Note: Input 2 has no function because of the direct input mod, just for looks.

I would change R101 to 150K and J102 to 1,5K on both driver boards. And don't forget to use shielded wire from RCA to the driver boards.

About the varistors: there are a lot of opinions on that. I replaced all with two 1N4148's in series to be sure.

View attachment 982410

View attachment 982411

View attachment 982412


I knew I saw where someone did this !

And did you try 100kohm at all and compare?

Regarding the varistors, I have seen debates on whether these are the same ones that sony used that killed the v-fet's in thier units. I just want to be sure ........ @Oilmaster what is recommended?

Athanasios
 
Sony used VD1221 double diodes (blue dip), as where the Yammie B-2 uses HV46R double diodes (red dip).
While being from the same manufacturer, same age, etc, the HV46R have very few / none reported issues, and many wise AK folks have quoted that replacement was not really required.
All the HV46R that I ever pulled from Yamaha gear where fine.
So.....

Furthermore, Sony put them in places and conditions where failure of the double diode is creating a mortal situation for the VFETs (hence the nickname "suicide diodes")
Inside the B-2, the failure of one of the double diodes would not lead to a VFET BBQ party.

I have yet to pick up a story where a failing double diode inside a B-2 had effectively killed a VFET. But vintage gear does supply us unlimited different cases, so....

2x 1N4148 in series is an adequate replacement for those double diodes, in case you would like to do it.
 
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WOW, its been three years since I got this amp and its still sitting where I left it.

But I just repaired ( easy fix) a Technics SU-9070 Pre amp and think this would be a perfect pre for the B2.

Now that there is more time as I have closed my restaurant for most of the week and just doing take outs on the weekends
I can get to work on this.

Now fist off, where do I start?

Remove the V-fets and test I guess is what most will say.

Check the filter caps to see if they are still good.

Then look at the known problem, the cracked input board. I may remove it and double check the repair work on it and see if I can
make it more reliable for testing the amp, clean the switches whit its out.


What else guys? Might start on this tonight.


PS what about my Curve tracer? Safe for testing V-fets? I have three from a Yamaha organ I can practice on just incase ;)



Athanasios
 
Got the front panel off and those Input switches and A/B speaker switches do not "click" like I assume they should.
One does sometimes , Input 2 .

So I'll have to remove that board and switches from the board and see if I can fix them or just get new ones.

Nashou
 
Pulled the switch board out from the from a bit to have a better look.

I can clean up the board and the added jumpers much nicer than who ever did this work.

Here you can see the cracked board . What I wonder is how the hell did that happen in the first place♂️

49701434688_da34ca9ecd_h.jpg



Here you can see the jumper wire de soldered .

49701434633_c0b9bec3a4_h.jpg


On this input GND wire they never added the PVC sleeve back on it.

49701434678_e3e986c40d_h.jpg



Ugly !!!

nashou
 
I'm very excited about this threads potential.
Long story short, like you, I have a shelved B-2 project that I should be getting to by the weekend (waiting on a few diodes and resistors to get my M-4 off the bench).
 
Well my switches are not functional 100% I got one to work. And these come all connected in a metal holder so one side is
held in place by the metal cover.

Here is the board removed of the switches.

49702429711_9128cc1f0b_b.jpg


49702429721_9128cc1f0b_b.jpg


And here is the metal cover that also acts as a top for the switches.

49701899428_6ca432e61b_b.jpg


I decided to put the switch that works for input 1 . Not sure what going to happen with the speaker switches . Is it pushed in speakers on, or the other way?

I might be able to use new switches and use the cover mount them. Will have to see what I can find unless @Oilmaster still has a switch board..........Or I by pass them and go that route....But i really had plans for two preamps connected .

Nashou
 
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my money is on a monkey trying to take it apart to clean the switches and breaking the board in the process.

Unfortunately, because of the irregular size of those switches, your only replacements would be used ones that were not abused.


Oh yeah I bet, I cleaned one and it was completely black oxidation. No way was there any signal getting through.


I think they are 4 pole switches 12 pins/3 pins per circuit = 4

I think I can use 4 of these F8UEE switches. I used them in My Yamaha A-960 and they worked great.
Wish I could get the gold plated ones but they are back order for 12 weeks. don't feel like waiting.

https://www.digikey.com/product-detail/en/c-k/F8UEE01A/CKN11865-ND/3862550

https://dznh3ojzb2azq.cloudfront.net/products/Pushbutton/F/documents/datasheet.pdf

F8UEE01A.JPG


49702673436_649ab23b28_b.jpg


I don't think the metal cover was for any shielding and just a chassis to connect them to the front
panel. and as part of the switch itself. I wonder how much they had to pay to her that made like that. Proprietary part I bet.



I'll order 4 and I am pretty sure I can make them work. If not at least I tried.

I'll just cut the pins off not used like the originals are.

One works but as the metal chassis is part of it I may not use it at all.

I'll use the existing chassis to mount them as I have a few ideas on how. If not I'll order one form the switch
maker. You can have then configured how you want them. So I might be able to get it close.

Nashou
 
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