Help troubleshooting Yamaha B-2 poweramp

Iluvatar

Vintage HI-FI Hunter
Hi,

I am the very happy owner of a Yamaha B-2 poweramp, but some problems have started to occur regularly, so I seek advice on correcting them.

First of, both of the red "dots" (LEDs?) on the left side on the faceplate have "died". Sometimes there is still a faint red light in the upper one, but thats it. How can I fix this?

Secondly, the sound in the left speaker channel sometimes disappears, but reappears if I turn the amp off and then on again. What could cause this and how can I fix this?

I have a little experience with soldering (or just about enough to not hurt myself).

Note: I have used Deoxit on the volume controls, and they work perfectly as far as I can tell (and hear).
 
For the channel out problem, it is most likely a 'dirty' speaker relay. When the channel is out, try tapping on the speaker relay and see if the dead channel is affected. to find the speaker relay, take the cover off, turn the unit on and after a couple of seconds, see where the 'click' is comming from. .....that's your speaker relay.

To fix it: IMO, it's best to desolder the relay from the board. The relay's cover is held in place at the cover's bottom edge at the longer sides of the relay body. The plastic 'barbs' on the base of the relay engage square holes in the cover. You have to spread the cover and slide it off. The relay armature is set in a hinge, held with a spring. carefully remove (and don't lose) the spring. Carefully take the armature off of the hinge, sliding the contacts out. Spray the contacts on the armature and on the base's contacts with deOxit. gently 'massage' the contacts with wet/dry (600 grit) sandpaper and try to maintain the contact's shape. Don't overdue it. There might be a layer of gold that you don't want to grind off. Be careful that you don't distort the shape of the armature or the position of the bases contacts.
Wipe off the residue and give a final light coating of Deoxit. reassemble and resolder.

The LED's are out? Well, with the unit on, measure the voltage across the LED's. You should get ~2.2~3volts across it. If you do and they are dark, replace the LED. If you get less than 2.2 V, turn off the unit and perform a diode test across the diode. If the diode test looks good, you'll need to find out why voltage isn't getting there. If the voltage across the diode is greater than 3.3 volts, the diode sounds open and should be replaced.
 
The periodic drop-out could also be the speaker and output switches on the front panel. Try to clean those internally too. See if it still happens if you use output 1 versus 2. I have found these switches to be "wanky" (that's a very technical term :nerd:) from time to time.
 
Have you cleaned any of the controls/switches yet ?
Also a Service Manual would come in handy , sorry I don't .

BTW welcome to Audiokarma , nice amp ....



Barney
 
First of, both of the red "dots" (LEDs?) on the left side on the faceplate have "died". Sometimes there is still a faint red light in the upper one, but thats it. How can I fix this?

The bottom LED only lights when the amp is in protection mode. Those LED's are held in place by foam that is stuck to the chassis. That foam turns to dust over the years and then the LED's can slip down in behind the front panel. Could it be that that's what has happened in yours?

Secondly, the sound in the left speaker channel sometimes disappears, but reappears if I turn the amp off and then on again. What could cause this and how can I fix this?

Lots of things can cause that but if you've already cleaned the controls and switches, I would check the relay for that channel.
 
Thanks for all the advice. There has been no problems with the left channel yesterday (or today yet), so I havent had a chance to check if it is indeed the relay.

The bottom LED only lights when the amp is in protection mode. Those LED's are held in place by foam that is stuck to the chassis. That foam turns to dust over the years and then the LED's can slip down in behind the front panel. Could it be that that's what has happened in yours?

The foam is still in ok shape, I had the faceplate off when I cleaned the switches, so its not because they have slipped down. When I first got the unit (around 3 months ago) both LED's worked fine, and so did the lights in the VU meters. Then all 4 of the meter bulbs died within 6 hours of each other, and after that the LED's started making trouble. Could it be signs that the unit needs a recap and that the voltage might be erratic in that part of the amp?
 
The foam is still in ok shape, I had the faceplate off when I cleaned the switches, so its not because they have slipped down. When I first got the unit (around 3 months ago) both LED's worked fine, and so did the lights in the VU meters. Then all 4 of the meter bulbs died within 6 hours of each other, and after that the LED's started making trouble. Could it be signs that the unit needs a recap and that the voltage might be erratic in that part of the amp?

The LED's and the VU meter lamps are powered from the same 12 V source. The alignment of the LED's in the front panel is somewhat critical. When I put my front panel back on, I didn't get them in the hole just right and at first I thought the LED's had died on me but when I looked more carefully I could see the misalignment. Your situation is likely different.
 
Thanks for all the advice. I have not dared to do anything yet (also waiting for replacement bulbs to arrive, so I'll probably take a look-see then), but I noticed something that might make it easier to troubleshoot the problem...

First of, the fall out of the left channel happens randomly, sometimes it plays for days with no problems, and then suddenly it reappears (the VU meter also stops showing any output).

Secondly, it seems that the left channel gets active again a split second after I turn the unit off (and the VU meter also responds just for a few mili-seconds).

Any of this make it easier to identify the problem with some certainty?
 
I 2nd the vote to clean the A B speaker switches and the Speaker On/Off buttons with DeOxit 1st and see if that doesn't solve your problem. My B-2 is in very good condition, having been gone through by Terry DeWick before I purchased it, but occasionally exhibits the same symptom. At first, I was very worried, but remembered reading that the speaker switches can be problematic. I turned off the power and just worked all three switches for maybe 30 to 50 times. When I turned the unit back on, everything was fine. I had to repeat this a few times over the course of a few days, but haven't had a problem since. I plan on going into the unit with some DeOxit soon, but at least now I feel confident that the problem is not something more serious. (Touches wood) :D

Good luck.
 
The B-2 is a great amp, but Yamaha used some pretty cheap-ass switches for the A-B speaker select. Clean them well, and it'll probably behave for a while.
 
I got my bulbs today, so I'm working on it. I think I found the relays, but wanted to be sure before I do anything rash. I've included a picture, are those the relays?

Thanks for the advice.

Echowars:
Would you recommend switching the relays for some of better quality, and do you have any suggestions?
 

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I followed some of the suggestions presented here about cleaning the switches. The relays look fine and healthy, so I decided not to go into that terrority for now... I'm really happy with the new bulbs, made the amp come more alive again! :D
 
Stock relays are fine, but I replace them during rebuilds as a preventative maintenence measure. LY2-0-DC12. Digikey #Z978-ND.
 
I have a spare set of relays, and no longer own a B-2. I'll send 'em to you for a very modest fee (shipping plus a cup of coffee or something like that).

PM me if interested.
 
Well, guess what...

My Yamaha just died 30 minutes ago :tears:

The VU meters still measure output, and work. The lights in both VU meters dont work, the red LEDs on the left dont work either, relays are not responding when switching speaker channels, and there is no sound from any of the channels. I have checked all fuses (there are 4 on the power board, where the relays are located too, and two near the "mains in", any others?), they seem to be fine. The VU meters respond when I turn the unit on and off, but nothing else does.

As mentioned above, I put new bulbs in the VU meters yesterday, could this have put stress on something that was bad before and caused this, or?

Does it sound like I really do need to do a recap? :scratch2:

HELP! :tears:
 
You can find it on page 20 of the manual, the power supply circuit board. It is marked, oddly enough, +12V.
 
I was wondering, could I check DC-offset on the AMP to determine if the vfets are dead or not, or would that be a waste of time, since there is no output anyway? I'm asking because I might be getting a multimeter today.
 
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