B-2 PS Fuses - Slow of Fast blow?

[Uncle Paul]

About them V-FETs

Now that I had access to the V-FETs, I went about pulling them one at a time for testing. After each was pulled it was tested and replaced before pulling the next one. I followed the EchoWars procedure that Vint Age provided. My DMM, however was reading 1.7 Ohms where it should have been reading 0, so for the purposes of the test I subtracted that from the voltages I read. It's possible that some of the measurements are off, so I will probably retest to validate with a more accurate DMM.

Results in the attachment. Even though my DMM might not have measured exactly accurate it certainly appears that the magic V-FETs are good.

This B-2 will ride again!

 

[Martin.Ca]

just in case you don't have the manuals
http://www.goodsoundclub.com/PDF/YamahaB2_Service.PDF
http://www.goodsoundclub.com/PDF/YamahaB2_Manual.PDF
http://www.goodsoundclub.com/PDF/YamahaB2_Report.PDF
http://www.goodsoundclub.com/PDF/YamahaB2_Circuit.PDF

Those are okay, but Yamaha printed in black, white & Red...

try this ...

http://sportsbil.com/yamaha/b-2-sm-s.pdf

 

[Vint Age]

WOW! It's amazing that the jumper board broke like that. It would have taken some serious force since it's a pretty solid little board. And just as amazing is that the FET's survived not one but two fuse blows since they likely were running with no bias during that time; a very stressful condition and a true testament to their ruggedness. :thmbsp:

I'll bet you'll be giving the whole amp a thorough inspection before powering it up again.

 

[Uncle Paul]

WOW! It's amazing that the jumper board broke like that. It would have taken some serious force since it's a pretty solid little board. And just as amazing is that the FET's survived not one but two fuse blows since they likely were running with no bias during that time; a very stressful condition and a true testament to their ruggedness. :thmbsp:

I'll bet you'll be giving the whole amp a thorough inspection before powering it up again.

Even after I saw the broken board I expected the V-FETs to be bad. In fact, when I tested the first one I had it upside down and got an open on the resistance test. I was really bummed thinking they were all probably blown. Then I recognized my mistake and the first one tested out, and then then next...

I've decided that repairing the connector cb would not be the best choice. Instead, when I get back from my current business trip I'm going to unsolder both pieces and take careful measurements so I can generate the gerber files for a replacement. I have a few other DIY projects planned that require high quality circuit boards, and I'll use this as a pilot. Kind of expensive, but it will allow me to inspect the work of the pcb manufacturer before I commit to much larger and more expensive boards.

I'm definitely planning on a full resto as this amp deserves it. I'm compiling a list of the caps, diodes, transistors, etc that are recommended for upgrade or replacement. I'm also going to detail the chassis (already pretty clean) while everything is out, and get to as much of an "as new" condition as possible. Also going to upgrade the RCA jacks.

The speaker terminals, while attractive, are my least favorite part of the amp. I just can't get them to bite hard enough to keep my speaker cables from wanting to work their way out. It's livable, but I'd really like to replace them with some quality binding posts. I'm not going to do it unless I can find a way to do it so that they are functional, attractive, and reversible.

The hard part now is putting it away for a while as I have other commitments (like finishing my home addition project), before I can devote time and money to this project. At least I have the M-4 I just bought from Avionic to listen to in the mean time

 

[Uncle Paul]

Those are okay, but Yamaha printed in black, white & Red...

try this ...

http://sportsbil.com/yamaha/b-2-sm-s.pdf

:thmbsp: Wow - that's the best version so far, much clearer and in color. The best part is that it has the first page of dissassembly that is missing from the other versions. That page, BTW, shows how to remove the V-FET module. I didn't know about the bottom panel or that the connector board had to be unsoldered for removal. If mine hadn't been broken, I'd have had one heck of a time getting it out without that knowledge.

Just found out that sportsbil.com is forum member's Njord Noatun's web site. Thank you very much for this terrific archive, Njord! :thmbsp:

 

[Vint Age]

I'm definitely planning on a full resto as this amp deserves it. I'm compiling a list of the caps, diodes, transistors, etc that are recommended for upgrade or replacement. I'm also going to detail the chassis (already pretty clean) while everything is out, and get to as much of an "as new" condition as possible. Also going to upgrade the RCA jacks.

The speaker terminals, while attractive, are my least favorite part of the amp. I just can't get them to bite hard enough to keep my speaker cables from wanting to work their way out. It's livable, but I'd really like to replace them with some quality binding posts. I'm not going to do it unless I can find a way to do it so that they are functional, attractive, and reversible.

I went a little crazy on mine and replaced all the carbon film resistors on the driver boards with metal film. I added some heatsinks to the 4 transistors on the right side of the driver board because they run pretty hot, recapped it except for the main PS caps, replaced the lamps with LED's and changed out the speaker connects with binding posts. I also replaced the protection relays which was the single most improvement to the sound that I noticed. It's playing sweetly in the background now. :tresbon:

 

[Uncle Paul]

I went a little crazy on mine and replaced all the carbon film resistors on the driver boards with metal film. I added some heatsinks to the 4 transistors on the right side of the driver board because they run pretty hot, recapped it except for the main PS caps, replaced the lamps with LED's and changed out the speaker connects with binding posts. I also replaced the protection relays which was the single most improvement to the sound that I noticed. It's playing sweetly in the background now. :tresbon:

Added to the list :yes: Any pix, especially the binding posts?

 

[Martin.Ca]

:thmbsp: Wow - that's the best version so far, much clearer and in color. The best part is that it has the first page of dissassembly that is missing from the other versions. That page, BTW, shows how to remove the V-FET module. I didn't know about the bottom panel or that the connector board had to be unsoldered for removal. If mine hadn't been broken, I'd have had one heck of a time getting it out without that knowledge.

Just found out that sportsbil.com is forum member's Njord Noatun's web site. Thank you very much for this terrific archive, Njord! :thmbsp:

And that's the scan I made of my manual (took a hell of a long time to find one).

 

[Uncle Paul]

And that's the scan I made of my manual (took a hell of a long time to find one).

Thank you kindly for dogging that down! It makes a HUGE difference!

 

[Vint Age]

Here's a few.

 

[Uncle Paul]

Here's a few.

Thanks - those posts ain't oogly at all! I'm pondering changing orientation at well so each pair is + - - + (looks like it's .75" horizontally as well as vertically).

 

[HypnoToad]

thought i had better post where i found the manuals
http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=11141#11141

It's a good thing that Romy posted those but don't read on as he says bad things about the B-2 but that's par for the course for Romy.:yes:

 

[Uncle Paul]

It's a good thing that Romy posted those but don't read on as he says bad things about the B-2 but that's par for the course for Romy.:yes:

Actually, I was planning on using all that "doesn't image, no bass" stuff to see if I could get my next one cheaper. "Yessir, I'll take that ugly, heavy, flat black thing off your hands and it won't cost you a thing. Sez right here it sounds like crap. Now you have room for that nice wave radio..."

 

[Saint Johnny]

Actually, I was planning on using all that "doesn't image, no bass" stuff to see if I could get my next one cheaper. "Yessir, I'll take that ugly, heavy, flat black thing off your hands and it won't cost you a thing. Sez right here it sounds like crap. Now you have room for that nice wave radio..."

:lmao:
Ahh if it were only that easy. If you succeed with that pitch, perhaps you can sell it to me?

 

[Vint Age]

(looks like it's .75" horizontally as well as vertically).

 

[Uncle Paul]

Looks like my eyeball gauges need calibration... I'll have to play a bit with some parts to see what can be done. The .8" width might just be enough.

I might be the only guy on a business trip to Las Vegas that can't wait to get home...

 

[Uncle Paul]

Time for an update

I've finally been back in town long enough to spend some time on the amp. Examining the broken board gave me some insight as to why it broke. This particular channel had been serviced before (one of the trim pots on the driver board has been replaced), and the connector board had been soldered in place so that there was tension between the front and back. There is about a 2mm gap in height difference between the pieces at the break. The break itself is where the bow tie shaped board narrows at the driver board end - a natural weak spot.

There is no way this board can be repaired (at least so I would feel good about it), so I have decided to make a replacement. I got some accurate measurements off of the unbroken one, which turns out to be metric. I started by drawing the pads and outline in CAD, then printed it out and carefully cut it to shape to validate that I got everything right. Then I used a 1 mm dia pushpin to make holes where the leads should go. The first mock up was 1 mm short, so I added the extra length and it slipped right on.

I decided to make the shape of the replacement board rectangular for the following reasons:

• It's simpler
• No place for a stress fracture to occur
• I can make the traces a bit wider while still providing more space between them
• It fits the area and does not interfere with airflow or anything else
• Cost to produce is the same

I really don't understand why Yamaha didn't do the same, though the bowtie looks a bit cooler.

Even though this is a simple board I could easily make, I'm going to send it to a service that makes custom PCB's since I have other projects I want to do this way and it's a simple first attempt (my first experience going this route). Besides, I really want to go first class with everything I do to this amp.

I just finished the initial layout in TraxMaker, which you see in the attachment. The pads are plated through (that's what the brown color means) The actual tracks in blue will be on the bottom, and the yellow portion is the artwork. Note that I've retained the bowtie in the design. I'm going to double check all dimensions and may make a few changes to the artwork before I submit the design for manufacture - probably something to indicate that it's a clone.

I'll be getting two as I want both side to be identical, even though it shouldn't make any difference. Lead time is approx 6 weeks, so I should see my boards around Christmas :yes:

 

[Martin.Ca]

I assume they dog-boned it originally to allow more air-flow. Have you consider making it two-piece with a row of male/female pin connectors? Of course that may be a terrible idea. There's a pretty good scan of the PCB in the Service Manual.

 

[Vint Age]

I assume they dog-boned it originally to allow more air-flow.

I was thinking the same thing. If you look at the picture I attached you can see that you'll be blocking some of the air flow over the V-FET's with a wider board. Will the amp fail because of that? Probably not but since the B-2 runs a little on the warm side I'd be wanting to keep things pretty much as they were ... :thmbsp: :yes:

 

[brutal]

When I think of all the old IBM computers that I rolled off the dock into a dumpster that had massive flat ribbon cables in them...

I wouldn't replace that part with another PCB, I'd be looking for a heavy flex cable.